Understanding How Quartz Movements Work

Electricity and Water Do Mix

The challenge with electricity lies in its invisibility, making it a bit tricky to grasp. To simplify, let’s draw a parallel with the flow of water through pipes.

In this course, we’ll only touch on the basics of electrical theory – just enough to comprehend and carry out fundamental electrical tests on quartz watches.

Let’s start by examining Figure 1. In this illustration, a pump propels water from its outlet, through the top pipe, into the radiator, and then back through the bottom pipe to the pump inlet.

Figure 1- Basic water circuit

The pump creates a specific pressure, and the radiator, with its numerous narrow passages, hinders the water flow.

For a given pump pressure, a certain amount of water circulates in the circuit. If we boost the pump pressure, the water flow increases; if we decrease it, the flow diminishes.

Adjusting the resistance of the radiator also plays a role. If we increase the radiator’s resistance, water flow decreases; if we decrease the resistance, the flow increases.

Therefore, the water’s movement in the circuit depends on two factors:

  1. The pressure from the pump (higher pressure leads to higher flow)
  2. The resistance of the radiator (higher resistance results in lower flow)

This concept will be crucial as we delve into the equivalent electrical circuit shown in Figure 2.

The battery is the equivalent of the pump, with the outlet being indicated by the longer bar (i.e. the positive terminal). It generates a certain electrical pressure. The electrical current flows out of the positive terminal of the battery and into the negative terminal.

The wires are the equivalent of the pipes, and carry the electricity.

The lamp is the equivalent of the radiator: it has a certain resistance to the flow of electricity.

Figure 2 — basic electrical circuit

As with the water analogy, if we increase the electrical pressure from the battery, we increase the flow of electricity in the circuit. Likewise, if we increase the resistance of the lamp, we reduce the flow of electricity in the circuit.

Now I will show you the measurement units for pressure, flow, and resistance, and show how they are related mathematically.

1.2 Electrical units

Electrical pressure is measured in volts (symbol V). A typical watch battery generates about 1.5 volts of electrical pressure.

Electrical resistance is measured in ohms (symbol Ω).

Electrical current flow is measured in amps (symbol A).

The relationship between them is extremely simple. Let us put some numbers into our diagram:

A pressure of 1 volt, applied to a resistance of 1 ohm, causes 1 amp of current to flow.

As you would expect, if we double the electrical pressure to 2 volts, we double the current flow to 2 amps.

If we put the electrical pressure back to 1 volt, but this time double the resistance to 2 ohms, the current halves to 1/2 amp.


1.3 Electrical Equations and Units

The term “electrical pressure” is rarely used nowadays; instead, we use the term voltage, which means the same thing.

The Equation

We can express the relationship mathematically:

We can rearrange the equation to calculate any of the other variables. For instance, if we know the voltage and the current, we can work out the resistance.

Finally, if we know the current and the resistance, we can determine the voltage.

voltage (in volts)=current (in amps)×resistance (in ohms) voltage

1.3 Multiples and Sub-multiples

For quartz watches, the current is often very small, measured in microamps. Understanding the multiples and sub-multiples of volts, amps, and ohms is crucial. These are indicated by prefixes:

  • mega (symbol: M): a million
  • kilo (symbol: k): a thousand
  • milli (symbol: m): a thousandth
  • micro (symbol: μ): a millionth

So, a resistor of one thousand ohms is written as 1 kΩ (when pronounced, we merge “kilo” and “ohms” to say “kilohms”).

A voltage of three thousandths of a volt is written as 3 mV (pronounced as three millivolts).

A current of five millionths of an amp is written as 5 μA (pronounced as five microamps).

With quartz watches, we typically work with volts and microamps.

1.4 Magnetism

While everyone is familiar with magnetism, let’s quickly remind ourselves of a few relevant points in the context of horology:

  1. Opposite poles (N — S) attract, while like poles (N — N, S — S) repel.
  2. Some materials can become permanent magnets.
  3. Some materials are magnetic (attracted to a magnet) but will not become permanent magnets themselves.
  4. By passing an electrical current through a coil of wire, we produce a magnetic field — an electromagnet.

The train in a quartz watch is driven by a stepper motor, which leverages the phenomena mentioned above.

2. Stepper Motors

2.1 Basic Layout

The stepper motor in a quartz watch comprises a permanent magnet rotor, a magnetic stator, and a coil. Figure 3 illustrates the fundamental layout. Dotted lines represent the magnetic field in the stator when a current flows through the coil. The stator functions as a magnetic circuit, carrying the magnetic field in a loop similar to how a wire carries electricity. When there is an air gap in the circuit, the two ends of the stator act as magnetic poles, known as pole faces. In the watch stepper motor, these faces are curved and “embrace” the rotor. The rotor includes a built-in permanent magnet, represented as a bar magnet on the diagram.

For clarity, moving forward, we will omit the dotted lines indicating the magnetic field.

Figure 3 — Layout of Stepper Motor

2.2 Operation

In Figure 4, the coil has current flowing in one direction, creating a magnetic field in the stator. The pole faces of the stator exhibit a north pole on the left face and a south pole on the right face. These poles, depicted in red, result from the current flowing in the coil (also shown in red).

Figure 4- current flowing in coil
Figure 5-current in coil has been reversed

As mentioned earlier, the rotor is a permanent magnet with its own north and south poles. The north pole of the rotor is attracted to the south pole of the stator, and vice versa, aligning the rotor in a specific position.

Let’s reverse the current in the coil (Figure 5). This action reverses the magnetic field in the stator, changing the poles on the pole faces. Now, the magnetic poles of the rotor face like poles on the stator (e.g., the north pole of the rotor faces the north pole of the stator). Since like poles repel, the rotor starts to spin, and as it turns, its poles become attracted to the opposite poles on the stator.

The result is that the rotor turns through 180 degrees (Figure 6). It could equally well turn in either direction, with the end result being the same. We’ll discuss how to control the direction of rotation shortly.

Imagine reversing the current in the coil again. Once more, like poles face each other, causing the rotor to spin through another 180 degrees until opposite poles face each other, similar to Figure 4. By switching the direction of the current in the coil, we can make the rotor flip through 180 degrees repeatedly.

Figure 6- rotor flips through 180 degrees
Figure 7-rotor is stable when current is removed

2.3 Current Pulses

An important point to note is that the poles of the rotor magnet are attracted to the pole faces on the stator even when no current is flowing in the coil. The rotor is stable when at rest, resisting any tendency to turn. Therefore, it’s not necessary to keep the current flowing in the coil continuously. A brief pulse of current, long enough to drive the rotor into the opposite position, suffices. The current can then be switched off, and the rotor remains in its new position (Figure 7).

In most watches, the current pulse is very brief—just a few milliseconds. Prolonging the pulse unnecessarily draws current and reduces battery life.

2.4 Running Speed

Understanding that each time we reverse the current in the coil, the rotor spins through 180 degrees, we can attach a pinion to the rotor, allowing it to drive a gear train. The frequency at which we reverse the current in the coil determines how fast the train runs. We’ll delve into generating this reversing current later on.

2.5 Controlling the Direction

The remaining challenge is how to control the direction in which the rotor turns. In our current depiction of the stepper motor, the rotor could turn either clockwise or anticlockwise. This flexibility is problematic since running the train and, consequently, the watch hands backward serves no practical purpose, aside from amusement.

To address this, we need to arrange for the rotor to rest slightly rotated in one direction, let’s say clockwise. This way, when we reverse the current in the coil, the repulsion effect will consistently turn the rotor clockwise. The reverse, turning anticlockwise, would require bringing the repelling poles closer together, which is not feasible.

The key to ensuring the rotor always turns in one direction is to make it rest slightly rotated. Figure 8 illustrates how this is achieved.

Figure 8 — Offset Rest Position of Rotor

Recall that the stator is made from magnetic material, so it attracts a permanent magnet like the rotor. By shaping the pole face as shown in Figure 8, the smallest gap between the rotor and the pole face is several degrees clockwise from horizontal. The rotor naturally rests with its pole faces adjacent to the closest point, positioning it several degrees clockwise from horizontal on our diagram. This offset ensures the rotor consistently turns clockwise. As before, we’ve indicated the induced magnetic poles in brackets.

On the next section, we present the complete sequence. Please study it until you are confident in your understanding.

3. The Quartz Crystal Oscillator

Now that we have a motor that converts current pulses into rotary motion, the rotation speed is determined by the frequency of the current pulses. To generate these pulses with precision, modern mechanical timekeepers, including quartz watches, use a resonant oscillator at their core. In the case of quartz watches, this oscillator is a tiny piece of quartz shaped like a tuning fork.

If you could “ping” a quartz tuning fork, you’d observe it vibrating at a constant frequency, with the vibrations lasting a long time. In essence, a quartz crystal acts somewhat like a tiny pendulum, with the elasticity of the quartz providing the restoring force rather than gravity.

Quartz possesses several advantageous properties. Firstly, it is less sensitive to temperature changes compared to a traditional pendulum, indicating a very low temperature error.

Secondly, the small and light nature of the quartz tuning fork means it is unaffected by gravity, ensuring it vibrates at the same frequency regardless of its position. Consequently, it exhibits no significant positional error.

Lastly, due to its small size, it is easy to encase a quartz crystal in a sealed container, rendering it insensitive to changes in barometric pressure. This results in no barometric error.

This combination of properties makes quartz an ideal material for timekeeping. If we can detect the vibrations of the quartz crystal and provide impulses to sustain its movement, we would have the foundation for a highly accurate timekeeping device.

This is where the piezo-electric effect come into play.

3.1 The piezo-electric effect

When a piece of quartz is bent, it generates a voltage across it (see Figure 16).

Figure 16 — Voltage Produced by Bending a Quartz Crystal

As a quartz crystal vibrates, it produces an alternating voltage across it, synchronized with the vibrations. This generated voltage is utilized to detect the vibrations of a quartz crystal, precisely what a quartz watch accomplishes.

There’s another fascinating aspect we haven’t discussed yet. As mentioned earlier, when a piece of quartz is bent, it generates a voltage across it. Conversely, applying a voltage to a piece of quartz causes it to bend (see Figure 17).

Figure 17 — Quartz Crystal Bends When a Voltage is Applied

These two phenomena together constitute the piezo-electric effect.

To sustain the vibrations of a quartz crystal, we can apply a voltage pulse to initiate its vibration and then measure the alternating voltage it produces during its oscillations. This process is similar to giving a pendulum a push and letting it swing back and forth.

In traditional pendulum clocks, a tiny push is provided to the pendulum with each swing, precisely timed as it moves the pallets along the teeth of the escape wheel.

Quartz oscillators operate on a similar principle. The crystal receives a small “push” with each cycle, sustaining its vibration. An electronic circuit tracks the vibration using the alternating voltage from the crystal and generates each push at the precise moment.

Thus, the quartz crystal, in conjunction with its electronic circuit (similar to the pendulum combined with its escapement), undergoes continuous oscillation at a fixed frequency. This oscillation serves as the foundation for a highly accurate timing source. We will explore in more detail how the electronic circuit utilizes the quartz crystals’ vibrations in a little bit.

4. Watch Batteries and Capacitors

4.1 Background

Battery-powered watches were experimented with in the 20th century. They gained popularity in the late 1950s, although they weren’t quartz watches at that time. Instead, they used small button cells named for their size and shape.

Three basic technologies were explored: electro-mechanically impelled balance, electronically impelled balance, and tuning fork. While these technologies performed well, they didn’t outshine mechanical watches enough to justify their higher cost. Battery-powered watches held a minor market share for two decades until the development of affordable quartz watches in the early 1980s.

The improvement in timekeeping was remarkable — quartz watches could keep time to a few seconds per week, and many managed a few seconds per month. For most users, they rarely needed adjustment, except for the switch between British Summer Time and Greenwich Mean Time (in the United Kingdom) and when the battery needed replacing.

The high sales volumes led to cost reductions, and soon a wide range of quartz watches became available at every price point in the market.

4.2 The Cell — Overview

All quartz watches require a supply of electricity to operate the electronic circuit, the crystal oscillator, and the time display. The majority of quartz watches use a battery, more accurately termed a cell.

All cells consist of two electrodes connected to the positive and negative terminals on the outside of the cell. An electrolyte is present between the electrodes. Electrical energy is produced by chemical reactions between the two terminals and the electrolyte.

Figure 18 — Basic Construction of a Button Cell

There are two fundamental types of cells to know about: the primary cell and the secondary cell. Additionally, there is the capacitor, which employs an entirely different technology and is not a cell but serves a similar purpose.

4.3 Primary Cell

The primary cell generates electricity as chemical reactions occur inside it. The original electrode materials undergo chemical transformation into non-reactive substances. Once all the original material has transformed, the chemical reactions cease, and the cell no longer generates electricity; it is exhausted or “flat.”

The primary cell provides electricity until it is depleted, at which point it needs to be discarded.

4.4 Secondary Cell

The secondary cell shares similarities with the primary cell in its construction, but it uses different materials, and its chemical reactions are reversible. In other words, if electrical current is forced “backwards” through the cell when it is exhausted, the original electrode materials are restored. Once all the electrode material returns to its original form, the cell can produce electricity as if it were new.

This process is known as recharging the cell. Secondary cells can be discharged and recharged several hundred times before degradation becomes a concern.

Therefore, the secondary cell functions like a “store” for electricity. From fully charged, it produces electrical current until it becomes fully discharged or flat. At that point, it needs to be recharged.

The ability to store electricity makes it suitable for use with systems that generate electricity. Examples include solar-powered watches and those powered by the movement of the wearer’s wrist.

4.5 Capacitor

A capacitor stores electricity and can be charged and discharged repeatedly, similar to a secondary cell. While capacitors and secondary cells are interchangeable in some roles, a capacitor can only store a small amount of electricity compared to a cell of similar size. Capacitors have a very useful feature that we will discuss later.

4.6 Cell Characteristics

There are five important characteristics of a cell:

  1. Voltage
  2. Capacity
  3. Size
  4. Internal Resistance
  5. Self-discharge

4.7 Voltage

The voltage produced by a cell depends on the materials it is made from. Here are three common types:

Mercury

The mercury cell, once widely used, produces around 1.35 volts. However, it is no longer manufactured due to environmental concerns associated with mercury use.

Silver Oxide

The silver oxide cell, now the predominant type, produces approximately 1.55 volts. It has replaced mercury cells entirely.

Lithium

The lithium cell generates a higher voltage of 3 volts. It finds application in power-demanding devices, such as backlights for digital displays or multi-function chronographs.

4.8 Cell Capacity

For both primary and secondary cells, the rate of chemical reactions is influenced by the amount of electrical current drawn from the cell. In other words, drawing more current accelerates chemical reactions, leading to quicker exhaustion. Therefore, a cell has a specific electrical capacity.

Since electrical current is measured in amps, but watch cells provide very small currents, we often use milliamps (thousandths of an amp). The capacity of a cell is measured in milliamp-hours (mAh). For instance, a 100 mAh cell can theoretically provide 100 mA for one hour. If you draw only 10 mA, it will last for ten hours, and at 1 mA, it will last for 100 hours. In each case, the current (in mA) multiplied by the time (in hours) equals 100.

A cell with a capacity of 200 mAh will provide twice the current for a given time or last twice as long at the same current, indicating it has double the capacity.

It’s important to note that drawing very high currents from a cell may exhaust it more quickly than the calculation suggests. Button cells are typically rated at their 100-hour capacity, meaning a 100 mAh cell will provide 1 mA for 100 hours.

Battery Life Calculation

Battery life can be calculated using the formula:

Battery life in months=Capacity of the battery in mAh × 1000 Consumption of the watch ×730 Battery life in months=Consumption of the watch × 730 Capacity of the battery in mAh×1000​

This formula helps estimate how long a battery will last based on its capacity and the average number of hours in a month.

Example: Watch caliber ETA 255.485 with a consumption of 1.06  μA.

4.9 Size

Button cells are designated by their height and diameter, both measured in millimeters. The general guideline is that larger cells tend to have higher capacities. Watch cells vary in size, with heights ranging from 0.9 mm to 5.4 mm and diameters between 4 mm and 11.6 mm.

4.10 Internal Resistance

The speed at which chemical reactions occur within a cell places limits on the maximum current it can provide. This limitation is akin to having a resistor inside the cell. As current is drawn, internal resistance causes the terminal voltage to decrease. The higher the internal resistance, the less current the cell can supply. Different cell types have different internal resistances, a topic we’ll revisit later.

4.11 Self-discharge

All cells gradually lose their charge even when in storage. For primary cells, this discharge reduces the cell’s capacity. Primary cells typically lose around 5% of their capacity annually. Therefore, a cell that has been in stock for a few years may have significantly diminished charge and a shorter service life.

Secondary cells also experience self-discharge, but at a higher rate than primary cells. Despite this, secondary cells can be recharged, eliminating the need for immediate disposal. Capacitors also lose their charge, at a rate similar to secondary cells.

While self-discharge is undesirable, it must sometimes be balanced against other cell characteristics, as discussed in Section 4.12.

4.12 Low Drain and High Drain Cells

Silver oxide primary cells come in two types: low drain and high drain.

Low Drain Cells: These cells have a high internal resistance, limiting the amount of current they can provide. As a result, they are unsuitable for applications requiring high current drain, such as watches with backlights or alarms. However, low drain cells have a very low rate of self-discharge and are highly resistant to electrolyte leakage, which could damage the movement. They are suitable for normal analog watches or digital watches without special functions.

High Drain Cells: These cells have a lower internal resistance, enabling them to supply higher currents. They are used in applications with higher power requirements, such as watches with backlighting or alarms. Most modern digital watches, especially those with multiple functions, require high drain silver oxide cells or more commonly, lithium cells with a 3-volt rating.

Low drain cells lose up to 5% of their charge per year, whereas high drain cells lose up to 10% per year. In addition, high drain cells are more prone to leakage when discharged.

Low drain cells use sodium hydroxide for the electrolyte. High drain cells use potassium hydroxide.

4.13 Discharge curve

It is instructive to look at the graph of voltage over time, as the various types of cell are discharged. The difference in voltage between the different cell technologies (mercury, silver oxide, and lithium) is clear.

Figure 19-discharge curve for common cell types and capacitor

Note that all three cell chemistries maintain an almost constant voltage as they discharge, with the voltage dropping off steeply right at the end of the cell’s life. This constant voltage is generally regarded as a good feature, but it has one significant disadvantage: it is not possible to predict the remaining charge in the cell by measuring its voltage (except at the point where it falls steeply right at the end, which we can use to detect end-of-life — EOL).

This might be important when we are using a secondary cell — if we knew the level of charge in it, we can decide whether it needs recharging.

Now observe the discharge curve of the capacitor. The voltage from the capacitor is directly proportional to the charge remaining in it. Therefore, simply by measuring the voltage, we can determine the exact level of charge and indicate to the user how much longer the watch is likely to run. The wider voltage range from the capacitor means we need more sophisticated electronic circuitry to handle it, but this is worth doing for some watches.


Seiko Kinetic

In Seiko Kinetic watches, electricity is generated by the movement of the wearer’s wrist. This electric charge is stored in either a capacitor or, more recently, in a rechargeable cell. When the watch is not in use, the stored electricity powers the watch. By measuring the voltage of the capacitor or cell, it is possible to estimate the remaining run-time before a recharge or replacement is needed.

In recent years, Seiko has transitioned from using capacitors to rechargeable cells. The newer cells have a significantly larger electrical capacity, providing a longer run-time when the watch is not worn. Unlike most rechargeable cells with flat discharge curves, Seiko developed a special cell chemistry. This chemistry results in a falling voltage as the cell discharges, allowing the watch to indicate the remaining charge without modifying the electronic circuitry.

4.15 End-of-life (EOL) indication

It would be inconvenient if a watch simply stopped when the cell became exhausted, without warning the user in advance. Quartz watches with a second hand almost invariably have an end-of-life (EOL) indication. Most watches fast-step the second hand through two, three, four, or five seconds, pausing for the appropriate time before fast-stepping again. Thus the watch keeps the correct time, but the unusual motion of the second hand alerts the user that a new cell is required.

Digital watches usually have a flashing element on the display to indicate EOL.

4.16 The disposal of watch batteries

You should dispose of watch batteries with respect for the environment. If there is a sufficient quantity, they can be sold to a registered scrap battery dealer. Otherwise, watch and clock batteries (which have little scrap value) can be taken to your Local Authority Recycling Centre and placed in the appropriate bin.

5 The quartz watch circuit

In Section 3, we saw how the electronic circuit in a quartz watch maintains the quartz crystal in oscillation. Most watch crystals vibrate at 32,768 Hz. A quartz watch mechanism with a second hand needs an electrical pulse once per second to operate the stepper motor that drives the train.

It turns out to be very simple to divide the frequency of an electrical signal by two, using just a few electronic components. The quartz watch circuit has a chain of such dividers, each halving the frequency until we arrive at the required one pulse per second.

The dividers are all embodied in a tiny integrated circuit mounted on a circuit board, along with the quartz crystal and a number of electrical connections.

You can treat the circuit like a “black box”: that is, it either works properly or it does not. They cannot be serviced or repaired, but on most movements, they can easily be replaced. Figure 20 shows a couple of quartz watch circuits; the black arrows indicated the quartz crystals.

Figure 20-typical quartz watch circuits

5.1 Inhibit (or Grounding) Switch

Most quartz analogue watches with seconds hands feature a stop switch, often referred to as an inhibit switch. When the crown is pulled out into the time-setting position, this switch stops the train, allowing the user to halt the watch with the second hand at 12. Subsequently, they can adjust the time precisely and start the watch at the exact moment, achieving accurate time setting within one second.

The setting mechanism activates a switch that signals the integrated circuit to cease sending pulses to the stepper motor. The switch comprises a contact on the circuit board and a lever connected to the main plate of the movement, serving as the positive terminal of the battery. When the watch needs to be stopped, bringing the lever into contact with the circuit board’s contact connects it to the main plate, signaling the integrated circuit to halt.

5.2 Setting the Rate

Quartz watch crystals, while highly accurate, may have slight variations in frequency. Typically specified as accurate to within 20 parts per million (+20 ppm), a 32,768 Hz crystal may operate within the range of 32,767.3 Hz to 32,768.7 Hz, resulting in a timekeeping error of nearly two seconds per day, either gaining or losing.

In older 20th-century quartz watches, a trimmer component on the circuit board was used to fine-tune the crystal’s frequency for precise accuracy. However, trimmers added cost and introduced potential reliability issues.

Modern quartz watches adopt a different approach called inhibition. The quartz crystal is made to operate slightly faster than 32,768 Hz, ensuring the watch gains time even if the crystal is at the lower end of its +20 ppm frequency tolerance.

The integrated circuit is set to drop, or inhibit, one or more pulses from the quartz crystal at regular intervals. During manufacture, the actual rate is measured, and by adjusting the number of pulses dropped, the net rate can be finely tuned. Some high-quality quartz movements using inhibition can achieve timekeeping accuracy within a second per week.

However, the inhibition approach results in a peculiar effect. The watch runs slightly fast for a few seconds, then pauses briefly before continuing. While this irregularity is imperceptible to the human eye, it becomes evident on a timing machine. Users and technicians need to be aware of this effect and consider the correct measurement interval, as indicated in the movement manufacturer’s documentation and quartz timing machines.

I will say more about adjusting the rate (if possible) when I service a quartz watch in part 2 of this lesson. Figure 21 shows a block diagram of the quartz circuit.

Figure 21 — block diagram showing the quartz electronic circuit

5.3 Summary

6 The Quartz Watch Train

As I discussed in Section 2, the stepper motor does one complete rotation every two seconds (for a seconds-stepping movement). We need to drive a seconds hand which rotates once per minute.

We achieve this reduction using a gear train.

You are already familiar with the trains used in mechanical watches, and the train in a quartz watch is very similar. That is, it uses wheels, pinions and arbors, with pivots that run in plates — Figure 22.

There are some differences worth pointing out, but first we will look at the components in the train.

Figure 22 —a typical quartz analogue train

The bridge, strictly a cock but the manufacturer’s Technical Information uses the term “train wheel bridge”, is secured with one screw; there are two steady pins to locate the bridge on the plate.

Here are the stator (Figure 23) and bridge (figure 24)

Figure 23-the stator
Figure 24-the bridge

When the bridge is removed the components can be seen more clearly — Figure 25.

Figure 25 —the bridge removed

It is a train, similar to the clock train that we have looked at earlier, but instead of a mainspring, the train is driven by the rotor. The pinion on the rotor drives the intermediate wheel; a pinion under the intermediate wheel turns with the intermediate and drives the second wheel. The arbor for the second wheel extends through the plate to carry the seconds hand and the second pinion drives the third wheel. A long pinion on the third arbor extends through the plate and turns the driving wheel — Figure 35.

The details of the rotor are given in Figure 26 and Figure 27.

Figure 26- the rotor, from above
Figure 27-the rotor , underside

The intermediate wheel, Figure 28 and Figure 29, is driven by the pinion on the rotor.

Figure 28-intermediate wheel from above
Figure 29- Intermediate wheel, underside

The second wheel, Figure 30 and Figure 31, is driven by the pinion on the intermediate arbor. The extended arbor passes through the plate and carries the seconds hand.

Figure 30-second wheel, underside
Figure 31- second wheel

The third wheel is driven by the pinion on the second arbor — Figure 32; the third pinion extends through the plate and turns the driving wheel.

Figure 32 — third wheel underside
Figure 33 — third wheel, from above

6.1 Torque

In a spring driven watch (or clock) or a weight driven clock the low-speed end of the train experiences a high level of torque. The components in the train must be robust enough to withstand the relatively high loading upon them.

There is no significant torque developed anywhere in the quartz train. The main reason is that the train is driven — by the stepper motor — from the high speed end of the train.

As we proceed back through the train to the seconds hand or motion work, the rotational speed of the wheels gets slower, and thus the train has the potential to develop more torque. However, it does not do so because there is no significant load on the train from the motion work (but see Section 6.6).

6.2 Materials

The lack of torque anywhere in the train means different materials can be used in its construction. In particular, plastic wheels and pinions — and often pivots — may be used. These can be injection-moulded, which greatly reduces the manufacturing costs. Also, some plastics are effectively self-lubricating, which reduces or eliminates the need for oiling.

Indeed, some quartz movements use plastic plates, cocks, or bridges in the train, again reducing costs. The train in Figure 34 has a plastic top plate (and bottom plate, though you cannot see it), and the red arrow points to a white plastic pivot.

Figure 34 — plastic plate and pivot

6.3 Wear

The second advantage of having little or no torque is that wear in a quartz movement train is almost unheard of.

6.4 Jewelling

The lack of wear and low torque levels mean there is much less need for jewelling in the train. Again this reduces the manufacturing costs. Compared with a mechanical watch, a quartz analogue watch has a much lower jewel count — quite often zero. The jewel count is no longer a good indication of the quality of the movement.

6.5 Jamming

There is one shortcoming that you may well come across in your bench work. The lack of torque in the train allows the manufacturer to reduce the drive power to the stepper motor, thus extending the battery life. Indeed, manufacturers go to a great deal of trouble to make the battery loading as low as possible. An unfortunate side effect of having very little spare torque is that the train is easily jammed by dirt or dust. Thus a good quality case, which prevents the ingress of dirt, is important.

6.6 Variable power

I mentioned earlier that there is no significant torque developed in a quartz train. Now I should enlarge upon that by pointing out that a calendar mechanism, where fitted, does indeed require somewhat more torque to operate than the normal time display. Although the torque is small by mechanical watch standards, it is still several times higher when the date indication is changing than that required during the rest of the day.

If we design our circuit and stepper motor with enough power to operate the calendar mechanism, it would waste power for much of the time.

The solution is rather ingenious. It turns out that, by sophisticated monitoring of the current in the stepper motor, it is possible to detect whether it has, in fact, successfully stepped. So, in normal operation, the duration of the electrical pulse to the motor is made as small as possible. If the motor should misstep due to a higher than normal torque loading, it is immediately driven with increasingly wider pulses until it steps properly. The width of subsequent pulses is gradually reduced until the motor missteps again (or the pulse width reaches a set minimum).

By monitoring the motor steps, we can reduce the power to the lowest possible level for a given torque loading. When the torque loading increases temporarily — such as during a calendar change — we can increase the motor power temporarily.

6.7 Battery life as an indication of trouble

This ability to cope with higher torque loads by varying the motor power has the side effect of making the movement less sensitive to disruption by dirt and dust, or by lubricant failure. However, the extra power fed to the motor reduces the battery life. Quite often, the only indication that a quartz mechanical watch needs a service is that the battery life is unexpectedly short.

All quartz movements have a specified operating current. If the measured current exceeds the specified current, it is a clear sign that the motor is drawing a higher current to develop increased torque to overcome problems (e.g., increased friction in the train). This is a valuable diagnostic technique and one that we will look at again later.

7 The motion work in a quartz watch

The friction drive arrangement is achieved by fitting the cannon pinion between the two “arms” of the driving wheel — Figure 35. The “arms” grip the cannon wheel so that the whole assembly will turn as the watch runs but, for setting the hands, the cannon pinion can be turned while the driving wheel remains stationary.

Figure 35- the cannon pinion and driving wheel

When the dial is removed, the motion work is revealed together with the date indicator and the mechanism for changing the date — Figure 36. The minute wheel is hidden by the retainer for the date indicator, and the hour wheel can be clearly seen.

Figure 36 — quartz watch, under dial work

The actual components for the motion work are conventional in design, apart from the friction drive arrangement described previously. A dial washer is present to ensure that the hour wheel is held in place. The dial washer is integral with the hour wheel and bears against the underside of the dial.

Figure 37 — quartz watch motion work

The driving wheel is turned by the third pinion as shown by the arrow = Figure 38; the cannon pinion turns the minute wheel.

Figure 38 — quartz watch motion work

The hour wheel is placed over the cannon pinion pipe and is turned by the minute pinion — Figure 39.

Figure 39 — quartz motion work

8 Keyless mechanism in a quartz watch

The term keyless mechanism refers to the components that are used when the stem is turned to set the time and, in this movement, to correct the date. Early mechanical watches required the use of a tiny key to wind the watch through a hole in the inner back of the case; the hands were moved with the key, either through another hole at the back or a square protruding through the centre of the minute hand. A new mechanism was introduced to use the watch crown or button for winding and hand setting; it was termed keyless work.

There are many variations in the design of quartz keyless work; one example will be described fully and another type will be shown later in this section.

This quartz watch has a stem which can be moved to three positions:

1) the stem fully pushed in — turning the crown has no effect,

2) the stem pulled out one position — correction of the date,

3) the stem pulled out two positions — correction of the time.

The keyless mechanism is situated on the back of the movement under the electronic module, beside the stem. The main components are shown in Figure 40.

Please note the term setting lever jumper in the Technical Information for this movement, but the component would usually be called setting lever spring. In this explanation, the manufacturer’s term will be used.

Figure 40 — keyless work

It will be easier to understand the function of each component if, instead of looking at the complete assembly, the function of each part is considered separately before placing it in the movement.

The stem is shown in Figure 41 together with the sliding pinion; the sliding pinion is inserted into the watch plate together with the stem. The flat end of the stem engages the slot in the sliding pinion. There is a groove on both the inner end of the stem and on the sliding pinion. When the stem is in the middle position, the sliding pinion engages the setting wheel on the yoke to adjust the date. When the stem is pulled out fully, the sliding pinion engages the setting wheel on the dial side of the plate to adjust the time.

Figure 41- stem and sliding pinion

When the stem is in position, the groove is visible through an aperture in the plate; similarly, the sliding pinion can be seen through another aperture – Figure 42. The friction spring and the date setting wheel will be used when the stem is in the second position for adjusting the date.

Figure 42 — stem groove and sliding pinion

The setting lever will be considered next. It is really an assembly of two components: the setting lever itself and a retainer made from thin spring steel. A pivot on the setting lever fits into the open hole in the retainer shown by the arrow – Figure 43.

Figure 43 — setting lever assembly

On the underside of the setting lever, there is a pivot that fits into a hole in the watch plate – Figure 44. The nib will engage the groove in the stem.

Figure 44 — setting lever pivot, on the underside

When the setting lever is fastened in position and the stem is moved in and out, the setting lever will rotate about its pivot, which turns in the plate – Figure 45.

Figure 45 — movement of the stem causes the setting lever to rotate

When the movement is in the case, the screw that is loosened to remove the stem is the screw that retains the setting lever in position. When this screw is loosened, the setting lever retainer springs away from the movement so that the nib on the setting lever is no longer engaging the groove in the stem. The stem can then be removed.

The setting lever is located in three positions; it is important that there is a positive engagement in each of these positions so that the operations of setting the date and the time are achieved reliably. Although it is not the next component to be fitted during the process of reassembly, the operation of the jumper will now be explained.

A projecting pin at the bottom of the setting lever engages notches in the setting lever jumper. The slender part of the jumper is springy, so that as the setting lever moves, the jumper is pushed away; it then springs back to help move the setting lever and to hold the pin in position. The three notches hold the setting lever, and hence the stem, in each of the three positions. The pin on the setting lever has been colored red to show the operation more clearly – Figure 46, Figure 47, Figure 48.

Figure 46 — stem, pushed fully in

Figure 47-stem, middle position -changing the date

The stop lever and switch act on a train wheel to brake the train. The part of the lever shown with the arrow blocks the train — Figure 49.

Figure 49 — stop lever and switch

This action commences in Figure 50, where the tail of the stop lever (1) is disengaged from the wheel which you can see through the aperture (2). If the stem is pulled out fully, to the position ready for adjusting the time, Figure 51, the setting lever engages the tail of the stop lever and causes it to rotate (1).

Figure 50 — stop lever not engaged

The stop lever then presses against the wheel shown in the aperture (2). The switch part of the stop lever and switch (3), now contacts a terminal on the underside of the electronic module — Figure 52.

Figure 52 — contact on circuit board

Figure 52- contact on circuit board

We must now return to the functional aspects of the keyless work — hand setting, and date correction. The yoke comprises a lever with a setting wheel permanently assembled together with a cam profile. There is also a nib which engages the groove in the sliding pinion and a projecting pin which acts on the stop lever and switch — Figure 53.

Figure 53 — yoke (assembled)

The yoke is fitted to the movement so that it can rotate about the hole at its lower end — Figure 54:

Figure 54 — yoke fitted to the movement

1) the nib (1) fits into the groove in the sliding pinion and keeps the teeth on the sliding pinion in engagement with the setting wheel. The sliding pinion meshes with the setting wheel in the three different positions of the stem,

2) the pin on the underside of the yoke (2) fits between the two “arms” of the stop lever and switch and holds the stop lever away from the wheel and the switch away from its contact,

3) a pin on the setting lever fits into the cam profile,(3)

4) the pin on the setting lever (4) holds the setting lever, and thus the stem and the yoke, in the stem fully pushed in position.

When the setting mechanism cover is in place, the various components are retained in position but free to move — Figure 55.

Figure 55 — the setting mechanism cover in place

The pin on the setting lever and the pin on the yoke indicate the different positions of the components. In Figure 55, the stem is pressed fully in; the setting lever pin (1) engaged in the first notch in the setting lever jumper:

1) the yoke is held by the pin (2) in the position where turning the stem, and therefore the sliding pinion, will rotate the setting wheel but not cause any further movement,

2) the stop lever and switch are held out of engagement by the pin on the underside of the yoke (3),

3) the setting wheel is not engaging the date setting wheel.

When the stem is pulled partly out (to the middle position) the pin on the setting lever (1) is engaged in the middle position on the setting lever jumper, Figure 56:

1) the pin on the setting lever (2) operating in the cam on the yoke has moved the yoke so that the setting wheel begins to engage the date setting wheel (4),

2) the pin on the underside of the yoke (3) is still holding the stop lever and switch out of engagement.

Figure 56 — the stem is in the middle position

Figure 58 shows the components in the same position as Figure 56 with the exception that the setting wheel (1) is now fully engaging the date setting wheel (2).

Figure 57 — setting wheel fully engages the date setting wheel

The stem and the yoke have not moved; both are in the middle position. The date setting wheel pivots on a short arbor that turns, not in a round hole but in a slot. This permits the actual position of the date setting wheel (2) to change slightly according to the direction of rotation of the stem and the direction of rotation of the setting wheel (1). When the stem is turned clockwise, the date setting wheel (1) is turned anticlockwise so that it pushes the date setting wheel (2) partly out of engagement. If the stem is turned anticlockwise, the setting wheel (1) turns clockwise and draws the position of the date setting wheel (2) closer so that it becomes fully engaged with the setting wheel (1).

To understand the reason for this movement of the date setting wheel, it is necessary to turn the movement over and look at the dial side of the plate. The date setting wheel is attached to a short arbor that passes through the movement. At the opposite end of the arbor, there is a “three-toothed” date corrector — shown by the arrow — Figure 58. The “three-toothed” date corrector is shown not engaging the date indicator — its usual position. It is held in this position by the friction spring seen bearing against the date setting wheel on the back of the movement — Figure 57.

When the stem is pushed fully in, the “three-toothed” date corrector is in the position shown in Figure 57. If the stem is pulled to the middle position and the stem turned clockwise, the “three-toothed” date corrector remains in this position.

Figure 58 — the ‘three-toothed date corrector’

If, however, the stem is turned anticlockwise, the date setting wheel moves into full engagement with the setting wheel, and the “three-toothed” date corrector moves to engage the teeth on the date indicator — Figure 59. You can just see the slot exposed now that the wheel has moved.

The result of turning the stem anticlockwise in the middle position is to rapidly correct the date.

Figure 59 — “three-toothed” date corrector engaging the date ring.

There is just one position of the stem that remains to be explained — when the stem is fully out for adjusting the hands — Figure 60.

Figure 60 — the stem is pulled out

When the stem has been pulled out fully, the pin on the setting lever (1) is engaged in the third position on the setting lever jumper — Figure 60:

1) the pin on the setting lever (2), operating in the cam on the yoke, has moved the yoke as far as possible so that the setting wheel is again disengaged from the date setting wheel,

2) the pin on the underside of the yoke (3) now allows the stop lever to press against the train wheel to arrest the train. The stop lever switch would be engaging the contact on the electronic module if the circuit had been replaced on the movement.

This position, when the stem has been pulled out fully, is used to adjust the hands, but to understand how this is achieved, it is necessary to turn the movement over.

The sliding pinion has been moved as far as possible by the nib on the yoke (5) — Figure 60. It now engages a setting wheel on the dial side of the movement plate — Figure 61. The setting wheel meshes with the minute wheel, which turns the cannon pinion; the minute wheel pinion will turn the hour wheel.

Figure 61 — setting the time

The friction drive arrangement for setting the time is a little different from that of a mechanical watch. When the watch is working with the train being driven by the stepper motor, the driving wheel is turned by a pinion in the train at the point shown by the arrow — Figure 61. When adjusting the time, the driving wheel cannot turn; it is held by the watch train. The cannon pinion is therefore a friction fit in the assembly comprising the cannon pinion and the driving wheel. When setting the time, the driving wheel is stationary, and the cannon pinion is turned, but while the watch is working, the cannon pinion and driving wheel turn together — Figure 61.

Different types of keyless mechanisms

There are many variations in keyless mechanisms, but the components and their function are similar. A brief explanation of an alternative will enable you to understand most of the different forms. In this instance, the keyless mechanism is positioned under the dial. The minute train bridge retains the date indicator and the keyless mechanism in place; the yoke spring and the friction spring for the “three-toothed” date corrector are an integral part of the minute train bridge — Figure 62.

Figure 62- a different keyless mechanism

When the minute train bridge is removed, the various components of the keyless mechanism can be seen. Although the various components are different in shape, the names are the same as we have used before — Figure 63.

Figure 63 —the components of the keyless mechanism

Figure 63 shows the position of the components when the stem is fully pushed in. In this position, when the stem is turned just the sliding pinion rotates:

1) The stem is similar to the stem you would find in a mechanical watch with a square section; the sliding pinion fits onto the square and therefore turns with the stem -— it is free to slide along the square part of the stem.

2) The setting lever has a nib that engages in a groove in the stem. As the stem is pulled out, the setting lever turns. In this instance, the cam that controls the position of the setting wheel is part of the setting lever. The pin that engages the setting lever jumper to hold the setting lever positively in each of the three positions is underneath the setting lever, indicated by arrow 1.

3) The setting wheel is pivoted on a lever — the double corrector operating lever. This lever rotates about a pivot (2); at the other end of the lever is a pin that fits into the cam on the setting lever. Therefore, when the stem is moved, the setting lever will turn and change the position of the setting wheel. It will move in or out of engagement with the minute wheel and the date correcting wheel.

4) In the position shown, the setting wheel is engaged with the date setting wheel.

5) The yoke fits into the groove in the sliding pinion and is moved by the cam profile of the setting lever shown by arrow 3.

6) The setting lever jumper is retained in a recess in the plate; the jumper has three notches to locate the pin on the underside of the setting lever (1).

If the stem is moved outwards to the middle position — Figure 64:

Figure 64 — the stem in the middle position

1) The nib on the setting lever (1), located in the groove in the stem, is moved outwards, causing the setting lever to rotate in the direction of the arrow.

2) Because the setting lever has rotated:

a) The pin on the underside of the setting lever (2) has moved into the middle notch on the setting lever jumper.

b) The pin on the double corrector operating lever (3), which is moved by the setting lever “cam,” has moved to the middle position of the “cam.” In this position, there has been little movement of the double corrector operating lever — the setting wheel is still engaging the date correcting wheel.

c) The profile of the setting lever (4) has rotated the yoke in the direction of the arrow. This has moved the sliding pinion in the direction of the arrow so that it now engages the setting wheel.

If the stem is turned with the stem in the middle position, the sliding pinion on the square portion of the stem will turn with the stem and rotate the date setting wheel and the “three toothed” date corrector. As with the previous keyless mechanism, the date correcting wheel is pivoted in a slot. If the stem is turned clockwise, the corrector moves in its slot to engage the “three toothed” date corrector with the teeth on the date indicator. When the stem is turned anti-clockwise, the “three-toothed” date corrector moves away from the date indicator.

When the stem is moved further out to the hand setting position — Figure 65:

1) The nib on the setting lever (1), located in the groove in the stem, is moved outwards, causing the setting lever to rotate in the direction of the arrow.

2) Because the setting lever has rotated:

a) The pin on the underside of the setting lever (2) has moved into the third notch on the setting lever jumper. The setting lever jumper can now be seen more clearly.

b) The pin on the double corrector operating lever (3), which is moved by the setting lever “cam,” has moved to the third position of the “cam.” This has rotated the double corrector operating lever so that the setting wheel now engages the minute wheel.

c) The profile of the setting lever (4) has rotated the yoke in the direction of the arrow. This has moved the sliding pinion in the direction of the arrow so that it remains engaged with the setting wheel. If the stem is turned with the stem in this position, the sliding pinion rotates the setting wheel and, therefore, the minute wheel to set the hands.

Figure 65 — stem in the hand setting position

In the section describing the first design of keyless work, the action and function of the stop lever and switch were explained. To show the stop lever and switch in this second version of a quartz keyless mechanism, it is necessary to turn the movement over and remove the upper magnetic screen, the electronic module, and a distance piece under the electronic module. The stop lever and switch can then be clearly seen — Figure 66.

Figure 66 — stop lever and switch

The purpose of the stop lever and switch in this keyless mechanism is exactly the same as that described previously but, in this instance, it is moved by the sliding pinion. An extension of the stop lever and switch, indicated by the arrow, engages the groove in the sliding pinion. When the sliding pinion is in the position for hand setting, the stop switch touches a contact on the electronic module, and the lever rests against a train wheel.

Figure 66 also shows the setting lever spring clip. The spring clip performs two functions:

1) It retains the setting lever in the plate. The setting lever turns when the stem is moved from one position to another. The pivot on the setting lever extends through the plate from the dial side, and the clip is attached to the back of the plate to secure it in position.

2) It enables the stem to be removed. The clip is made from spring steel so that when the end of the setting lever pivot is pressed, the setting lever nib is moved out of engagement with the groove in the stem, allowing the stem to be removed —

Figure 67 — releasing the stem

9 The Date Change Mechanism in a Quartz Watch

The date change mechanism is located under the dial, and the components are illustrated in Figure 68.

Figure 68 — Date Change Components

In Figure 68, you can see the date indicator and driving wheel. The intermediate date wheel has a small pinion underneath that meshes with the date indicator driving wheel.

Assembled components are depicted in Figure 69. The hour wheel (1) drives the intermediate date wheel (2). Beneath the intermediate date wheel, a small pinion turns the date indicator driving wheel (3). The hour wheel (1) completes one rotation every twelve hours, while the date indicator driving wheel (3) rotates once every twenty-four hours. The date indicator fits between a flange and the date indicator driving wheel, featuring a projection that engages a tooth on the date indicator every twenty-four hours, advancing it by one day.

Figure 69 — Assembled Date Mechanism

The date jumper (4), shown in Figure 69, serves several functions:

1) Completes the movement of the date indicator — Figure 70.

2) Ensures the date indicator remains stationary — Figure 71.

3) Ensures the date indicator is securely held in the correct position for the date to be centered in the aperture.

Figure 70-date jumper about to advance the date indicator

Figure 71-Date Jumper locating the date indicator

The retaining plate plays a crucial role in securing the date jumper in place and allowing the date indicator to rotate freely.

It ensures that the date indicator remains in place while still enabling its rotation. To facilitate proper alignment and rotation of the date indicator, the minute train bridge is positioned opposite the retaining plate, as depicted in Figure 72.

Figure 72 — The Minute Train Bridge

10 The Liquid Crystal Display (LCD)

In our previous discussions, we focused on quartz watches with an analogue display—featuring a regular dial with hands.

However, some individuals prefer a digital time representation. Moreover, certain intricate functions like calendars, alarms, and interval timers are more efficiently managed with a digital display.

Among various digital display types, the liquid crystal display (LCD) is the one of interest in this course.

Figure 73 — Liquid Crystal Display (LCD) Module

LCDs are cost-effective to manufacture and highly versatile—they can be configured to showcase nearly anything. Additionally, they boast exceptionally low power consumption, making them ideal for watches. You might have encountered watches that combine a traditional analogue display for hours and minutes with an LCD for seconds. This design avoids the battery strain associated with one-second stepping of a stepper motor while providing the convenience of an analogue display with a one-second readout when needed.

However, LCDs have a notable drawback: they lack self-illumination and cannot be made luminous like conventional watch hands. Therefore, LCDs require a backlight to be visible in the dark, consuming a significant amount of power compared to the watch mechanism itself. Consequently, many such watches employ a 3 V lithium cell to address this power demand.

10.1 Construction and Operation

Understanding the intricacies of how an LCD works isn’t necessary since there’s little you can do to repair or service one.

In essence, an LCD comprises two glass pieces with a thin liquid layer between them, forming a sandwich structure.

Transparent electrodes on the inner surfaces of the glass create the segments of each digit or any special symbols the LCD may display. These transparent electrodes connect to terminals at the LCD’s edge for electrical access. By applying a voltage to specific connections, one or more segments can be rendered opaque.

To clarify, an un-energized segment in a liquid crystal display (LCD) is transparent, revealing the reflective backing strip (typically silver) behind it. When energized, the segment turns opaque, concealing the silver backing and presenting a black appearance.

In Figure 73, where the module is removed from the watch, all segments are in their transparent state, displaying the reflective background (appearing orangey-brown in this instance).

The specific mechanism behind the segment’s transition to opacity is not crucial for our purposes. If the segment doesn’t function, the recommended course of action is to replace the entire LCD.

10.2 Connection to the Circuit

However, an improperly functioning LCD may not solely result from a malfunctioning segment.

The LCD electrodes extend to terminals along one edge of the display, and connecting them to the circuit board requires a special conductive rubber strip. This strip, seen in Figure 74, comprises alternating conductive and insulating layers. It facilitates the flow of electricity across the strip, from the circuit board to the LCD, without allowing it to travel along the length of the strip. The strip is compressed between the circuit board and the LCD. Misplacement or the presence of dirt between the terminals and the strip can cause issues, leading to malfunctions in one or more LCD segments. Fortunately, addressing these problems is straightforward.

Figure 74-layered conductive strip

In Figure 75, observe the row of terminals along the bottom edge of the circuit, the connector strip, and the LCD module.

Figure 75- LCD module with connectorstrip and circuit

Moving to Figure 76, the LCD is now mounted in the movement, seen from its back. The connector strip is in position, making contact with the terminals along the edge of the LCD module. The black arrow indicates the opposite edge of the strip, which will connect with the row of terminals on the circuit. The circuit, visible in the image, is poised to be positioned over the LCD and connector strip.

Figure 76- LCD module in situ

10.3.1 Cleaning Circuit Board Terminals

The terminals on the circuit board may become dull over time, with a minute film of oxide potentially interfering with the electrical connection.

Since these terminals are delicate, avoid using harsh abrasives. Instead, employ a dry leather buff stick on the circuit board terminals. Gently rub them two or three times to restore a shiny surface.

10.3.2 Cleaning Connector Strip and LCD Terminals

Cleaning the top and bottom surfaces of the rubber strip and the terminals on the LCD may be necessary. Use a blower to remove dust, and if needed, a leather buff stick or a soft cloth. Avoid cleaning fluids, as they can cause the rubber strip to swell, damaging the component.

Ensure surfaces are free of fibers or dust before reassembling to prevent interference with electrical connections.

In most cases, these cleaning steps can restore a digital readout to good working order. LCD failures are rare but can occur due to careless handling or severe shocks, leading to opaque patches. In such cases, replacement with a new part is the only solution.

11 Tests for Quartz Watches

There are several simple tests crucial for servicing a quartz watch. Some require access to the manufacturer’s data for the movement. Below, we’ll explore a couple of popular multi-function testers designed for testing quartz watch movements.

11.1 Before and After Tests

Perform these tests before stripping and servicing the watch as powerful diagnostic tools. Diagnosing the issue beforehand is essential to avoid working blindly. After remedial work, repeat these tests and compare the results with the originals to confirm the fault correction and ensure the watch operates within the manufacturer’s parameters.

11.2 Battery Voltage Test

The simplest test involves measuring the battery voltage. However, a straightforward voltage measurement may not provide insights into the battery’s condition. Watch batteries often show a healthy voltage even when nearly exhausted. Additional tests are needed to assess the battery properly.

11.3 Drive Pulses

The circuit generates electrical pulses fed to the stepper motor coil. If the battery is okay but the stepper motor isn’t running, connect your quartz tester to the coil terminals to check for drive pulses. These are indicated by a brief flicker of the numerical display or an LED flashing. Some testers can detect pulses magnetically, even with the watch back on, but an electrical connection to the coil terminals is crucial to identify issues with the coil.

11.4 Current Consumption

We mentioned in Section 6.6 that many modern quartz movements send more power to the stepper motor in order to overcome excessive friction in the train, or to cope with the intermittent load from the calendar mechanism.

This manifests itself as a greater current drain on the battery. By measuring the current consumption of the movement, we can get a very good indication of whether it is suffering from excessive frictional losses. Of course, we need to know what the current consumption should normally be, and for this we must consult the manufacturer’s data sheet for that movement.

The current drawn from the battery varies enormously. Each second (or less frequently in watches without seconds hands) there is a large pulse of current to operate the stepper motor. Between the pulses there is a more-or-less constant, but small, current to operate the integrated circuit.

Rather than measure these separately, it is customary to measure the average current. The measurement interval may be several seconds, and again, the manufacturer’s data sheet will indicate the recommended test duration.

It is not feasible to measure the current consumption using a simple multimeter without modification due to the need both to measure the average current over several steps and the need to interrupt the circuit from the battery in order to connect the multimeter in series with it. However, all popular multi-function quartz watch testers provide this testing ability. The battery is removed from the watch movement, and two probes from the tester are touched onto the battery terminals in the movement. Thus the tester provides the operating voltage in lieu of the battery, and measures the current consumption of the movement.

Note that some manufacturers specify an operating current for the circuit alone —that is, when disconnected from the stepper motor. This test is very useful for
identifying a faulty circuit. If specified, you should definitely perform this test.

11.5 Grounding switch

As previously mentioned, the grounding switch (also known as the inhibit switch, but not to be confused with pulse inhibition mentioned earlier) is employed to halt the stepper motor during time setting. It is activated by pulling the stem out to the hand-setting position (not the date setting position). A small lever in the mechanism connects a terminal on the circuit board to the main plate (the positive terminal of the battery), signaling the circuit to stop pulsing the stepper motor.

The current drawn by the movement should decrease to a small, steady level, as only the circuit itself is in operation.

11.6 Low voltage indication

Nearly all modern quartz watches with seconds hands feature a low voltage (or end-of-life (EOL)) indication to alert the owner that a new battery is needed. This typically involves an unusual stepping pattern for the seconds hand. For example, it may rapidly step through five seconds and then pause. Some movements provide a double-step every two seconds. Watches with LCD displays usually show a low-battery symbol.

The manufacturer will specify the voltage at which the low voltage indication begins to operate. However, if you don’t have access to the relevant data sheet, a figure of around 1.3 volts is typical.

As with the current consumption measurement, this test must be performed using a quartz watch tester. The tester enables you to decrease the voltage supplied to the watch in small steps while observing the second hand.

11.7 Lower working voltage

The watch should continue to run and keep time even when giving a low voltage indication. Eventually, however, the voltage will fall too low for the watch to operate, and the lowest voltage at which the watch should run is specified by the manufacturer.

Note the terminology: “lower working voltage.” This means that the watch must work at the specified voltage, not that it must stop at—or immediately below—that voltage, as some people may think. In reality, most movements in good condition will continue to operate somewhat below the specified lower working voltage.

Like the low voltage indication test, this test requires a quartz watch tester. This will enable you to reduce the operating voltage while observing the motion of the second hand.

11.8 Coil Resistance

The stepper motor coil is crafted with thousands of turns of fine and delicate enamelled copper wire. The wire’s long length imparts electrical resistance, typically ranging from several hundred ohms to a few thousand ohms.

Coils seldom malfunction on their own, but they are prone to damage, especially when someone uses a knife blade to open the watch back. If the back pops off, the blade may skid over the movement, potentially scraping and breaking the coil turns on the outer surface.

This damage can result in the coil becoming an open circuit, meaning its resistance becomes infinite. In extremely rare cases, the insulation on the copper wire might fail, causing some turns to become shorted out. This shortening reduces the effective length of the wire and lowers the overall resistance.

The most effective way to assess the coil’s health is to measure its resistance and compare it with the manufacturer’s specifications. This test is usually conducted with the coil and circuit in place, with the watch battery removed. The measurement probes are placed on the two coil connections, and the resistance is read from the tester. Notably, this is one of the few tests that can be equally well-performed with a regular multimeter.

Even without access to the manufacturer’s data sheet, a higher resistance than specified or exceeding around 2kΩ (in the absence of specific information) suggests a faulty coil.

If the multimeter or tester indicates an unusually low resistance (ohms or tens of ohms), it’s advisable to electrically isolate the coil from the circuit board and repeat the test. This is done to ensure that a fault on the circuit board is not causing a false reading. However, this step should only be taken if you are reasonably sure that the coil or circuit board is faulty.

A faulty coil should be replaced, as attempting a repair is possible but highly impractical.

11.9 Coil Insulation

The coil is electrically isolated from the main plate of the watch, but there is a possibility that the insulation may be damaged. This can be checked using quartz testers set to the highest resistance range. With the battery removed, place one probe on the movement main plate and touch the other probe to the two coil terminals in turn. The tester should indicate high resistance (zero conductivity).

I do not recommend testing the coil insulation unless other checks indicate potential damage to the insulation. Further details about testing the coil will be discussed in part 3 of this lesson.

11.11 Rate

It is probably obvious that an instrument for measuring the rate of a quartz watch must be significantly more accurate than the watch under test, in order for you to trust the readings.

Bearing in mind the high accuracy of modern quartz movements, this implies the need for a very sophisticated timing machine with a highly accurate and stable timebase. Although these are readily available they are expensive, and thus you may well not have access to one.

Furthermore, many modern quartz watches have no means of adjusting the rate, so there would be nothing you could do to correct one that was otherwise in good order but kept poor time. The only remedy would be to replace the entire circuit.

In fact, a poor rate is almost unheard of in modern quartz watches — they normally either work or do not work. However, you may occasionally find a quartz watch which loses to a noticeable extent. This is most likely due to intermittent sticking of the train due to dirt ingress or lubricant failure, and indicates the need for a service.

Only the older quartz watches, with trimmers, really benefit from a tester that will measure the rate. In this case, the watch can be brought to time, much like adjusting the rate of a mechanical watch.

Sensors for detecting the rate

Quartz watch testers usually have more than one sensor for detecting the rate, and you need to be aware of the differences.

Acoustic pickup: this detects two possible sound sources. The first is the 32768 Hz mechanical vibration from the quartz crystal itself The second source is the sound of the stepper motor.

For watches using inhibition, this is a crucial difference. Monitoring the crystal directly is useless because, as we discussed in Section 5.2, they are deliberately set to run slightly fast. For these watches, the acoustic sensor must be used to monitor the stepper motor. Note that the sound from the stepper motor and its associated gear train is inherently “noisy”, which means that obtaining a reliable indication of the rate may not always be achievable.

Older watches with trimmers are best set using the sensor to monitor the crystal frequency, because the trimmer adjusts the crystal frequency directly. You will get “noise” than the stepper motor vibrations and do not need averaging out over several seconds.

Magnetic or inductive pickup: these work by detecting the pulsating magnetic field from the stepper motor. They do not suffer the noise problem that blights the acoustic sensor, although in some watches the magnetic pulses are too weak to detect and the acoustic sensor must be used. As a general rule, you should try the magnetic sensor first, only using the acoustic sensor if necessary.

Capacitive pickup: these work by detecting the tiny alternating electric field produced by the quartz oscillator. Again, they are of no use in watches that use inhibition.