Troubleshooting and Testing

system and a mechanical system.

Which of these two systems is causing the problem is the first thing we need to figure out.

Because an electrical problem may be quick and easy to fix, and sometimes a mechanical problem typically can be solved quick and easy as well. Sometimes though it requires a full service of the movement, or you may decide that it’s in your best interest just to replace the full movement because a full service might not be warranted based on the value of the watch or the quartz movement.

This troubleshooting chart is adapted from the one in Citizens Tech Guides for quartz watches.

This is a troubleshooting workflow, which if you follow it will help you find the issue. It is not the only workflow that will help you find the problem. You can do these things in a different order but this one is pretty efficient.

There may be one that might be a little more efficient, but I’m going to not really discuss the efficiency of the troubleshooting process to a large extent and just rather what you can learn from each step.

So, let’s look at where you might go with your testing first and what conclusions you might draw along each step in the process.

For example, looking at this chart, it says if the watch is stopped, you’re going to check and see first is the quartz crystal vibrating. Do you have a signal from the quartz vibrating?

If you do, you’re going to jump to # 3 and you’re going to check screw tightness and check to see if all the connections are good.

If the crystal is not vibrating, you’re going to start with # 1 by testing power cell voltage.

Then it just goes through all the different steps from there until you get to the end when you should have a working watch if you follow those steps.

1 Testing quartz analogue movements

In the service video, the particular watch that we have serviced was not working; the battery was tested and found to be practically dead. When the average consumption of the movement was tested using a 1.55 volt supply, the result was 3 times higher than that recommended by the manufacturer. After cleaning, the average consumption was within the manufacturer’s specification indicating that servicing had been required to remove dirt and thickened oil. This is a very common scenario but the situation could have been different.

The tests that were used during the servicing of our watch provided information about:

  •  battery voltage under load,
  •  average movement consumption,
  •  consumption of the integrated circuit,
  •  coil resistance,

Detailed theoretical information about quartz watch testing is provided in the first part of this lesson but this section complements that information by demonstrating the practice and application of these tests. For my testing the Horotec FlashTest is used, but there are more sophisticated, much more expensive testing equipment available.

The Horotec testing equipment provides a highly sophisticated and powerful tool to diagnose faults in quartz watch movements at a fairly low price for this type of equipment— Figure 107. As well as the routine tests described, the stepping motor and the mechanical parts of the quartz analogue watch can be tested with the signal generator, independently of the electronic circuit.

Figure 107 — Horotec Flashtest

1.1 A summary of fault diagnosis for quartz watches

A significant part of any servicing procedure is to identify faults; this can be done both by inspection and by testing. For a quartz watch, there is an initial visual inspection of the watch with a functional test of the keyless work. Electrical testing should then begin; there are two reasons for performing the electrical tests when changing a battery or before servicing the watch:

  • it helps diagnose problems,
  •  it lets you compare the performance before and after the service

1.2 Initial Inspection

Before opening the watch, find out from as much information as possible from the seller or customer, and then test it yourself.

  • For instance, is the watch running at all? Look closely at the seconds hand (if one is fitted). If you can see it twitch once a second (but not stepping on) it strongly suggests that the train is jammed by dirt.  If the second hand is totally immobile, the watch may have a dead battery, or there may be some other mechanical or electrical fault.
  • If the second hand is not moving, move the crown out and in a few times.  Virtually all quartz watches have a mechanism for stopping the hands when the crown is pulled out for time setting. Sometimes the mechanism my stick and be freed for a short time by working the crown.
  • The watch may be showing a low-battery indication — this is indicated by the second hand double or quadruple-stepping. That is, the seconds hand makes two rapid steps every two seconds (or four every four seconds), rather than the normal once-per-second step. This is normally a sign that the battery needs replacing, although sometimes a circuit defect can cause the same problem.
  •  Check the proper operation of the keyless work for setting the time, and the date. If the watch has a three-position crown so that the date can be changed directly, pull the crown out into the middle position and check that the date change works in that mode. Then pull the crown out to the second position and set the hands forward through 12 o’clock, until the date changes. Make sure that the date changes smoothly and there is no obvious extra resistance to turning the crown.
  •  Make a note of the time at which the date changes. After the service you will set the date change to take place at the same time. The only exception is if it is obviously wrong (out by some hours).
  •  A watch which steams up in cold weather has moisture inside it. This will cause corrosion and stoppage. You will need to repair the damage; seals should be routinely replaced whenever a watch has been opened.
  • A watch that has stopped may not necessarily require servicing. Older quartz watches particularly may malfunction if exposed to strong magnetic fields. Analogue watches may stop in a steady (unidirectional) magnetic field or run fast in an alternating field. The circuit in digital watches and multi-function analogue watches may “freeze” due to exposure to a magnetic field. In each case, there should generally be no lasting effects on the watch and the watch can be set running again by briefly connecting the ‘AC’ terminal on the circuit to the main plate. The ‘AC’ terminal, If present, Is typically a small silver or gold colored dot marked AC on the back of the movement. If there is no ‘AC’ terminal present, removing and replacing the battery should resolve the problem.
  •  Finally, examine the case for signs of damage (cracked glass, scratches, a damaged strap or bracelet, etc.) Also check for signs of severe knocks — another sign that the watch may have been damaged.

 1.3 Testing the battery

  • The most common reason for movement stoppage is battery failure. Some people will install the wrong type of battery, or use old stock, such that the watch runs for a short while and then stops. Having had the battery changed recently, the customer naturally assumes there is a fault in the watch.

 Is it the right type of battery?

There are high and low drain batteries. Low drain cells are more resistant to leakage than high drain cells, so you should not substitute a high drain cell in a watch that is designed for a low drain cell. As a general rule, high drain cells are only required for watches which require intermittent high loads on the battery. These would include alarm watches, chronographs, watches with backlights, and so on.

 The majority of wristwatches, which just show the time and date, require the low drain type.

The Swiss tend to use a three-digit numbering scheme for their watch cells; the identification number does not provide any information about the cell. You need a conversion chart, or a specification sheet for the cell.

 The Japanese system tells you a lot more about the cell, and although you only need to know about one letter, we will quickly go over the rest of the numbering system.

 Here is a typical Japanese battery number — Figure 108

The letter we are interested in is the ‘S’ before the W. The ‘S’ means the cell is low drain type. The absence of an “S” means the cell is a high drain type.

What do you do if you find a Swiss battery with the three-digit numbering scheme? Simply use your conversion chart. For instance, the 371 is equivalent to the

SR92Z0SW, which means it must be a low drain cell. The 370, on the other hand, is equivalent to the SR920W, which makes it a high drain cell. Note that the 370 and 371 have identical physical dimensions and the same voltage rating of 1.5V. They even have the same capacity rating: 38mAh.

With the FlashTest, the battery can be tested either in the watch by using the probes or by removing the battery; the load on the battery can be varied to simulate the consumption of the integrated circuit and the stepping motor.

Figure 109 —test points for battery voltage

If the battery is removed from the movement, it should be placed with the positive part of the casing resting in the terminal on the FlashTest; the negative fly lead is placed on the battery negative terminal.

If the battery is faulty, replace the battery or continue with further tests using an external supply.

1.4 Coil drive pulses

If the seconds hand is stepping, or you can see the train moving, you know that pulses must be reaching the stepper motor so there is little point in testing for them. However, if the movement is not running, this is a very useful test; the absence of pulses to the stepper motor suggests a problem with the circuit, coil or battery. If pulses are present but the motor is not stepping, the coil or motor is faulty or the train is jammed. When a watch with a center seconds hand is placed on the signal sensor of the watch master, the signal indicator should illuminate every second to show that there are pulses to the stepper motor.

If the battery has been replaced or you are using an external supply but there are no coil drive impulses- replace the electronic module.

If there are coil drive impulses but the second hand does not move it is likely that the stepping motor/ train is blocked.

1.5 Movement Consumption

The base consumption tells you the condition of the IC and the baseline should be published in the tech sheets. If the base consumption value is higher, lower or way out of whack from what it’s supposed to be, it tells you either there’s no power getting to the circuitry, so there’s no consumption at all, or there’s some kind of a short.

That’s the only thing really that can go wrong with base consumption. So, unless you are repairing circuitry, it’s time for a new circuit.

The total consumption, which includes the motor impulses, will give you some information about the condition of the gear train or other possible mechanical faults.

If the total consumption is high, it typically means that either there’s something wrong with the coil or the gear train.

So, from the consumption test, if it’s high, go test your coil. If your coil resistance is within range, then it’s a mechanical fault.

That might mean it needs to be cleaned and serviced. The oils are old and gummy, there’s dirt or debris or lint in the movement that’s dragging the gear train.

There might be a piece of metal shaving stuck to the rotor. It’s a magnet so if there’s any metal shavings in there, that’s where they’re going to go. It might be rubbing, causing it to run inefficiently, but it might also be hands touching the crystal or the dial or each other.

Maybe the dial foot is broken or bent causing the dial to be off center and the dial hole is touching or rubbing against the post as the hands turn. And as I mentioned earlier, maybe that coil has got some damage.

Unlike a mechanical watch, quartz movements operate under a very small amount of torque. This is why jewels are not needed as much. Anything including a speck of dust can stop a quartz movement from running.

After battery testing, measuring the current consumptions of the movement are probably the most powerful tools used to find faults with the watch. There are two aspects to measuring consumption, the consumption of the integrated circuit and the average consumption of the movement. Assuming that the second hand is moving, the consumption of the movement can be tested by connecting the test instrument to the test points on the movement- figure 110

The average consumption of the 955.112 movement should be tested using a 1.55 Volt power supply with the stem pushed fully in. As the term average consumption indicates, it is a measure of the consumption of both the integrated circuit and the stepping motor. The consumption of the integrated circuit does not vary but, if there is more resistance in the train, the stepping motor consumption will increase, thus the average consumption also will be higher.

Figure 110-test points for consumption

  • stem in for average consumption
  • stem out for integrated circuit consumption

If the stem is pulled out, the stop lever and switch operate to stop the stepping motor and the test measures just the consumption of the integrated circuit. The watch master measures both aspects of consumption even when the stem is pressed in. At the start of the test, the consumption of the integrated circuit is shown on the screen but after 5 seconds the average consumption is displayed. The watch master automatically determines the period of time necessary for an accurate measurement of average consumption.

If the average consumption is higher than the manufacturer’s technical information it is likely that the movement requires cleaning to remove dirt and thickened oil.

If the consumption does not reduce when the stem is pulled out, the stop lever and switch is faulty.

Factors that affect Consumption

There are multiple factors which affect the consumption and the battery life of the movement.

  1. Condition of the coil.

If the coil has a short in it, it will have less resistance and it will consume more electricity so the battery will not last as long.

  • If it has a dead short to ground, the battery will probably be dead in a couple of minutes.
  • The mechanics of the watch also affect the consumption of the battery.

The harder it is to turn the motor, the more electricity is used by the watch, whether or not there’s special programming like inhibition in the watch movement or not.

Think of it like this. If you’ve ever been at your polishing motor and you’ve really put the bracelet or ring or whatever it is your polishing and really drove that into the motor and you can feel the resistance of the motor, the motor is really having a drag put on it.

If it’s harder to turn the motor, it’s going to draw more electricity to make that happen.

  • the next thing that can affect the consumption of battery life is the programming of the watch, whether it has inhibition or not.
  • And of course, the trimmer. As you rotate that trimmer, you are forcing the crystal to vibrate not in its natural frequency. so, it takes more electricity to force that crystal to vibrate unnaturally than it does for it to vibrate naturally.

The trimmers should be paired to the natural frequency of the crystal as closely as possible. But if you have to turn that thing a lot to get the rate back to normal, you may also notice your consumption go up in that watch and the battery life shortened.

The Gear Train

Interruptions in the gear train are connected to the electrical and will cause consumption to go up.

If the gear train is completely blocked, you’re going to see asservissement kick in and you’re going to see your consumption levels go up.

Even if you don’t have asservissement you’re still going to see those consumptions go up because it’s trying to force the train to rotate.

Things that can cause the consumption to go up based on the gear train are debris or dirt in the gear train, a bent wheel or metal shavings that might have gotten in there.

The date change

When we’re testing consumption levels, we need to make sure that the date is not engaged, otherwise we’re going to get higher readings.

High consumption levels can also be something beyond the gear train. It might be the hands rubbing on the crystal, or even when you have a watch that has steel hands because high carbon steel hands, can become magnetized.

With magnetized hands, as they go past one another, they’re attracted to each other, and the motor has to work a little harder to get those hands to push past each other so consumption goes up.

If you’ve got a watch with steel hands, you might make sure those hands aren’t over top of each other. Make sure they’re 180 degrees apart when you do this test to make sure they’re not affecting the consumption test. And, of course, demagnetizing them so that they don’t attract each other there.

And I’m going to show you a couple of times where I mess with the gear train here so you

can see those effects.

The Hands

This is something that is often overlooked, but it’s a common place for problems in any watch. The hands should be horizontal to each other and certainly not touching anything, that’s going to produce a drag on the motor, or it may stop it completely.

1.5 End of life operation and lower working voltage

When the battery voltage falls, modern movements generally have a feature which comes into operation to warn the user that the battery requires replacement which is indicated by the seconds hand stepping once every four seconds.

EOL (end of life) can only be checked with a variable voltage supply. Some more advanced testers can provide a supply at 1.55, 1.35, 1.25 or 1.1 volts (and also 3 volts and 2.1 volts). The same test points are used as for the consumption tests but, after first testing the average consumption, the supply voltage is reduced to 1.35 volts.

If the voltage is reduced below 1.3 volts, the movement will continue working in EOL mode until, after successive reductions in voltage, it will eventually stop. The voltage at which it stops is the lower working voltage. It is a measure of the condition of the movement. If the train requires attention because of dirt and congealed oil, the lower working voltage will be higher than if the watch has just been serviced. A lower working voltage of 1.1 volts or less is typical.

Rather than considering the lower working voltage, it is preferable to commence with a power supply of voltage below the anticipated lower working voltage and gradually increase the voltage until the watch starts. The watch-master does not have this facility.

If EOL function does not work, there is a fault in the electronic module requiring replacement of the module.

If the watch ceases to work at a voltage greater than the lower working voltage, it will require servicing.

1.6. Accelerated testing

Many movements have an additional test point sometimes designated the T point ‘or the R/T point. If it is connected to the negative probe, the stepper motor moves at a faster rate — Figure 111 — which offers several useful functions:

Figure 111 — using the T point

  • It can be used to accelerate the date changeover around midnight in order to check whether there are any problems due to stiffness with the date ring or its actuating mechanism,
  • If the watch has no seconds hand, the pulse rate to the stepper motor may be one step every five seconds or even as low as one step every 30 seconds. Using the T point enables the operation of the stepping motor to be observed instantly,
  • It can give a speedier indication of EOL operation for slow stepping motors ( watches without a second hand ).

1.7 Other tests

There are two other tests which can be undertaken to determine whether the coil is damaged: coil resistance and coil insulation.

With the battery removed use the Flash Tester with these coil connection test points — Figure 112 and Figure 113

Figure 112- test points for coil resistance

Figure 113- test points for coil insulation

If the coil resistance or coil insulation shows that there is a fault with the coil, the coil or IC will have to be replaced.

If there are pulses to the coil and there is no fault with the coil, it is likely to be a mechanical fault such as the rotor or train jammed or the hands touching.

1.8 Testing the coil resistance

I mentioned that if you’ve got problems with consumption the next thing you do is test your coil resistance. You’re going to look for the condition of the coil. It may be cut or damaged in some small way.

Typically, this happens when somebody’s tool slips when they’re opening the watch and certainly if that happens to you, you need to replace the coil, so make the repair.

If the coil is open, you’ll have no motor pulses at all, and your resistance will be infinity

Usually there are two motor points labeled with an M on an ETA circuit where you can put the positive and negative ones to get that with the test meter in the resistance section.

Or there are little gold colored connection points near the coil. You do need to be careful though, that typically if they’re the two right next to the coil, that’s where the wires are connected for the coil and the wires are super small.

You need to be careful not to damage those wires as you’re testing the resistance. You want to stay away from the wires coming out of that.

The battery should be out of the watch when you test the coil resistance, otherwise you’ll be getting the resistance of the battery in addition to the resistance of the coil by itself.

If the coil can be removed, if it’s separate from the rest of the circuitry, you should test it disconnected from the rest of the circuitry.

The coil can also have a short in it and it can be short in a couple of different ways.

It can be shorted to the IC.

When that happens, what you will get is an asymmetrical consumption value, meaning one pulse will have one value and the next one will have a different value and it’ll alternate back and forth between those two.

That’s because of the different energy flows to the coil, unless it’s cut exactly in the middle, you’ll be getting different amounts of the coil each time as the energy flows.

Different amounts of energy from the coil mean different resistance, mean different consumption.

The watch usually won’t work, it might work, but usually it doesn’t, but you will see those alternating consumption values.

The consumption will always be high when there’s a short because there’s less coil, less wire, which means less resistance, and less resistance means the energy flows more easily through it and so you get a higher consumption usage.

The other way it can short out is to itself.

The most common thing that causes this to happen is when somebody has run something against the coil and then they’ve gone to repair it with some of that epoxy or something like it and so this repair has caused the electricity to skip over some of the coils and short across.

That’s what it’s going to do.

It’s going to short out the cut coils or missed coils, but it is possible for the watch to run still.

You don’t need every single coil for the watch to run, but it will run with a higher consumption and there will be less power available to drive the watch, so it may stop sooner as the condition deteriorates.

Short story is if any of the values of the coil are out of tolerance, you really should replace the coil.

Repairing the coil is reserved for only when coils absolutely aren’t available. If a coil is available, that is preferable, the coil or the complete circuit with the coil attached to any repair when possible.

The electronic module includes the coil, the integrated circuit and the quartz crystal oscillator; it can only be replaced as a unit. The coil is the most likely component within the electronic module to be damaged or become defective; it can be easily tested.

The resistance of the coil will show whether the fine copper wire from which the coil is made has been damaged. Stepper motor coils are extremely delicate and they sometimes become open circuit due to a break in the wire. In this case the resistance measures as infinite. Very rarely there may be a short circuit, in which case the resistance measures as zero, or just a few ohms.

The normal resistance range is between several hundred ohms and a few thousand ohms (kilohms (kΩ)). If the coil resistance is in that range, you can normally assume the coil is not defective. A reading of “infinite” or “open circuit” indicates a faulty coil, as does a reading of zero, or just a few, ohms.

To use the FlashTest, set the test mode to “resist”; the battery should be removed and the test leads applied to the coil terminals — Figure 114.

Figure 114 — the test points to check the coil

The result given by the Flash Test was within the figure given in the technical Information for the 955.112 movement (1.3 — 1.8 kΩ) — Figure 115.

Figure 115 —test result for coil resistance

1.10 The three levels of test equipment.

Simple battery testers

With a battery tester, the only thing you can test is the battery’s voltage, which is good information, but absolutely the minimum that you need.

Multimeters

With a multimeter, you can still test the battery voltage and you can typically test the coil resistance as well.

Advanced Testers

Testers like the Horotec Flash Test that I use, the Witschi New Tech Handy II, the Analyzer Q1, Analyzer or even the Greiner Compact 900

With this advanced technology, you get better tests which are needed to troubleshoot quartz movements.

You can test the rate of the quartz oscillator, the rate of the motor impulses, the consumption of the circuitry by itself or the consumption of the circuitry including with the motor rotating.

You can test for the presence and function of the end-of-life indicator (EOL), asservissement, or you can test the lower working limit to see how efficiently it’s running.

In the most recent equipment, you can test the pulse width and drive efficiency tests.

You also have a pulse generator tester, which is useful for doing tests on chronographs and alarm movements and other quality or troubleshooting with those types of watches.

The Horotec FlashTest is an example of test equipment which fulfils a lot of the most important range of tests that are routinely used to diagnose faults in quartz analogue movements. Unfortunately test instruments of this kind are expensive and it is hard for the student or home watchmaker to justify the expense. There are no low cost alternatives which will achieve the complete range of tests. We shall briefly examine some of the options which can be purchased.

Battery testing

There are battery testers which can be bought at an economical price; this example has terminals for testing high drain cells, low drain cells, and also 3V lithium cells — Figure 118.

We will not be using the 3 volt terminal at this stage. The difference between the two 1.5 volt terminals is that the high-drain terminal puts a higher load on the cell when it is under test.

Place the positive terminal of the battery downwards onto the appropriate terminal of the tester. The positive terminal is the large outer case of the cell — the smaller terminal surrounded by insulation is the negative one. Touch the negative terminal with the flying lead and the needle will move to the right. Check that it is in the Figure 118 —a low cost battery tester green range on the scale marked “SILVER”. If it is, the battery is OK.

Figure 118- low cost battery tester

There is a “MERCURY” scale; in the early days of electronic watches, the cells contained mercury and generated a lower voltage — about 1.35V. These are no longer available, so you can safely ignore the mercury scale on the meter.

The voltage of a battery can be tested with a multimeter but that merely shows the output of the battery without any load. Watch batteries maintain a high voltage until almost exhausted; a battery tested under load gives better information about the actual condition of the battery.

Another alternative commercial testing instruments will be mentioned; unfortunately it’s readily available through material dealers, the Seiko S-860 — Figure 119. It must be remembered that this test instrument lack the sophistication of the more expensive Witschi testers; they can, nevertheless, provide a useful function.

Figure 119- Seiko S-860 tester

The Horotec Flash Test I am using, covers the most important tests for home watchmakers, but lacks many of the more advanced features found in the Witschi Q1 used in service centers or major shops

* The “turbo” feature is available on some other watch testing instruments enable the watch hands to be rotated quickly with the intention of “unjamming” the train, hands and calendar parts.

The Seiko S-860 tester has the facility to adjust the period of time and the voltage supply for testing the average consumption of the movement. The period or “gate” is important. Movements without a seconds hand may only receive a pulse to the stepping motor every 20, 30 or even 60 seconds; the gate must be set according to the time interval of the watch being moved to ensure a stepping motor pulse is within the test period — Figure 120.

Figure 120 — the Seiko tester set to measure average consumption

When the watch is placed on the receiver, the Horotec Flashtest indicates the stepping motor pulses by a visual display and an audible signal — Figure 121.

Figure 121 — the Horotec Flashtest

The Seiko instrument can be set to 3 V, 2.4 V and 1.55 V; the Flash Tester can be adjusted to test movements requiring 1.55 V and 3 V.

Figure 122 — the tester can be set at 1.55 V and 3 V

1.11 More about battery removal

The movement we have serviced used a bridle or spring clip to secure the battery, but there are other approaches. There are two basic types: spring clips and bridges.

Bridges are less often found on modern watches. They span the battery and are held down at each end by screws. Some have a slot at one end, so that the screws simply have to be loosened and the bridge will swing clear of the battery. Others require you to remove one of the screws completely.

Some watches have a metal cover over the whole movement, which includes a spring to retain the battery. In this case you will need to remove the metal cover first. The black arrows in Figure 139 show the two screws which must be removed to release the cover. Once the cover has been removed and the battery can be flicked out with tweezers or a fine screwdriver.

Figure 139-this cover must be removed first to give access to the battery

Figure 140 — the cover removed, giving access to the battery

Never use your fingers or metal tweezers to hold or manipulate a watch battery. The tweezers will short circuit the battery, ruining it. Fingerprints cause corrosion and bad connections; usually some time after the battery has been fitted. Use plastic tweezers instead.

In some movements, the coil is more exposed than the ETA 955.112. Always take great care not to touch the stepper motor coil — indicated by the black arrow in Figure 140. The wires are very fine and delicate, and easily damaged.

1.12 Rate adjustment

All mechanical watches need their rate adjusted after servicing, but with quartz watches this almost always NOT possible.

Rate adjustment systems

Trimmer

A trimmer is an adjustable capacitor that you rotate like a screw. It’s actually a cam, but it looks like a screw on the top of it and by turning it, you change the capacitance of the capacitor, which forces the crystal to vibrate slightly differently to get a little different rate of pulses from the crystal. With the trimmer system, as the watchmaker, you can adjust the rate by moving the trimmer a little bit one way or the direction.

It’s usually a different color than the other screws that you can identify on the movement When you turn a trimmer, you should use a non-conductive tool to rotate it. They make special screwdrivers for trimmers. If you go to Amazon and look for a screwdriver for trimmers, it’ll probably have a ceramic blade.

If you don’t use an insulated screwdriver, it doesn’t do any permanent damage but just keep in mind that when checking the rate, the reading is going to not be accurate until after a couple minutes.

This is technology that for the most part hasn’t been used for a while, but you still see movements with trimmers come across your bench.

Fixed Capacitor

When a manufacture times out the crystal, then they can put a fixed capacitor in the IC, which forces the crystal to vibrate at the right speed. This is often used in stopwatches, and you wouldn’t see it used very much in wristwatches. Fixed capacitors can only be adjusted in the production process.

Inhibition

The quartz crystal by itself vibrates at 32,768 beats per second, which is what we see in modern quartz watches and is very easily accurate to a couple of seconds a day. With some correction and some control, they can be much more accurate than that.

Quartz watches maintain precision through the rhythmic vibrations of quartz crystals. Inhibition constantly monitors quartz crystal vibrations and automatically detects and corrects deviations caused by external factors like temperature changes.

With this digital rate correction provided by inhibition, quartz was now able to increase the accuracy to the range of 10 or 20 seconds a month.

Imagine this tiny crystal that vibrates 32,768 times a second. The Integrated circuit or IC takes these vibrations and splits them in half a bunch of times.

Now, every 32,768th vibration, it’s like the circuit says, “Alright, motor, it’s your turn to do something!” It ignores the other vibrations and only pays attention to that special last one.

But sometimes the crystal vibrates a bit too fast, and you get 32,769 vibrations instead. The watch uses the inhibition system. It will count up to 32,768 for 59 times (once a second), and on the 60th cycle, it doesn’t count as high. Depending on how the circuit has been programed, It might stop at 32,760 and then it will throw away the extra eight vibrations to make the adjustment.

By doing this, Inhibition corrects for the fast vibrations, making sure the average rate over a minute is just right. This makes the motor in the watch keep time more accurate than if it relied only on the 32,768 vibrations of the crystal.

This inhibition system is always adjusted in production and cannot be adjusted without very expensive equipment.

Typically, if there is a problem with the rate and there is not a trimmer screw, you’re just going to replace the circuitry.

When we measure the rate by listening to the motor instead of listening to the crystal vibrating, we’re measuring the magnetic field that’s generated when the rotor turns. You are actually measuring how often the motor is turned on to force the gear train to move. You are in a sense, when checking the rate measured at the motor, making sure that inhibition is functioning properly.

This rate measured from the motor is given as seconds per month.

What can affect the Rate

  1. It’s affected by the programming of the watch or by the trimmer if there is one.

In the case of the trimmer, you can make those adjustments and changing the rate of the programming is not very common.

Trimmer adjusted watches

Adjustment of the trimmer “pulls” the frequency of vibration of the crystal itself away from its unloaded natural frequency, so the best way to measure the rate is by setting up the timing machine with an acoustic sensor to detect the mechanical vibrations of the crystal itself. The trimmer capacitor should always be adjusted with a plastic screwdriver — see Figure 141.

Figure 141- with trimmer capacitor

Pulse inhibition watches

These watches cannot be timed using acoustic pick-ups. A magnetic or inductive pick-up must be used to pick up the pulsating field from a stepper motor. There are several types of pulse inhibition, many of which are programmed by the manufacturer and cannot be adjusted. If the rate is poor there is little that can be done other than to replace the entire circuit board.

There is one type however which does permit rate adjustment and an example is shown in Figure 141.

Figure 142- with pulse inhibition capacitor

By touching the relevant gain or lose contact indicated by the arrow the rate can be adjusted by 0.33 seconds per month for each touch. As these watches are every accurate, unless the watch is very badly adjusted a general purpose timing machine is unlikely to be of sufficient accuracy to be of much use.

If a specialist timing machine is used, care must be taken to ensure that you do not sample the crystal frequency and that the sampling period includes the inhibition interval. Quartz watch timing machines normally accommodate this automatically.