How To Test Quartz Crystals Found  In Watches

By on April 25, 2019
How To Test Quartz Crystals Found  In Watches

 

 

 

 

 

 

 

 

 

 

 

This article will I think be very interesting for those of us who want to test those special tiny common quartz crystals like used in all modern electronic watches and all sorts of timers. Especially if you like me have a couple of them laying around and want to find out if they are still working. And we also find these crystals on all PC mainboards for running the Real Time Clock (on board RTC chip). Most circuits sadly only are able to test the larger quartz crystals without any problem but do not operate on the crystals that are used in modern watches. The oscillating energy coming from these smaller watch crystals is just too little for most circuits to generate a noticeable oscillating sinus signal on the output.

how to test quartz crystal

So above on eBay and many other online internet sites sold quartz crystal tester fails to test these special watch crystals. They only are able to test the ordinary bigger crystals up to about 50 MHz. Although nice and not expensive above kit complete with programmed PIC processor, display and plexiglass housing fails for being useful in our case.




Therefore another option would be to use an older used LCD watch that still works and on which we can easily measure on the crystal pins. I did this by connecting 1.5V DC to the watch in next photos and measured with my scope probe directly on one of both crystal pins while it was working. And the ground of my scope pin I just connected to the ground of the 1.5V DC input.

My Tektronix 2465A scope showed a perfectly oscillating quartz crystal with a frequency of 32768 Hz.

So this already looks like a splendid test device for our watch crystals. Still I wanted to test other circuits to see if I could test these crystals in other ways than by using an old digital LCD watch. Also because a watch is very tiny and fragile and not perfectly suited to replace it with other crystals.

test quartz crystal

Next photo of my scope screen shows a perfectly generating sinus signal.

waveform of quartz crystal

waveform of quartz crystal testing

Previous photo showed how my Tektronix scope probed the oscillating crystal by using a red wire pinned onto the inner quartz pin. To make sure my watch crystal tester also works with other frequencies than the standard 32,768 KHz this old watch as test device could be a problem in case the watch won’t oscillate on other frequencies. So I tested a few other circuits on an experimenter’s board.

quartz crystal tester diagram

Above circuit was no good and even had trouble with the standard quartz crystals. (I used another BC547 type so that could be the cause of it not working. But they normally have a fT of around 100 MHz so that can’t be it).




Next FET circuit on the right worked splendidly with normal crystals but again not with our tiny watch crystals. But at least it worked right away with ordinary crystals.

And maybe next Pierce circuit works like it is used in many microprocessor Xtal oscillating circuits but I didn’t try out. Also because I decided to use a watch crystal tester around a good old CD4060 CMOS IC.

cmos ic crystal

The principle of all oscillating circuits is to amplify at least with a factor higher than 1 with positive feedback to the input of our amplifier so that it starts oscillating. If the amplification is less it simply refuses to oscillate. And in our case with the very small quartz crystals the amplification must be able to amplify the very small energy of our crystals to a level that it reaches a stable oscillation. For oscillation following rules apply: when amplification (gain) A = Uout/Uin, and when 1/3 of the output is feedback to the input we need to make sure that 1/3 x A = 1 so that oscillation will start. Or if 1/3 is feedback factor k we need to make sure that 1/k >=A. So in this case A would be at least a gain of 3,333 or higher to compensate for circuit losses and to keep the positive feedback alive. Because the

crystal simulation circuit

crystal diagram simulation circuit

energy coming of our crystal is so tiny we need an amplifier that compensates this. So the starting amplification will be much higher at the start before a stable oscillation is reached. And in watches this is compensated by a circuit that at the start amplifies the noise that is generated in the tiny crystal before it is a stable sinus oscillation. Previous photo showed a simple and perfect working watch crystal tester on a experimenter’s board that can be used with most if not all of those tiny quartz crystals.




It uses a standard CD4060 CMOS IC and the resistors and capacitors are not critical at all! I used a 2.2Mohm plus a 330Kohm resistor, plus two 33pF capacitors on the legs of the quartz under test. But other component values probably will work too. All that is needed is an oscilloscope and a 5V power supply to feed this little tester. All my quartz crystals tested fine with this tester.

how to test quartz crystal accurately

And none of those very expensive watch maker’s tools I’ve seen on the internet is able to test only the quartz crystals if removed from their boards. They in general just test the timing of the complete working watches and are not capable of testing the crystals.

Seeing all those very professional priced tools that only the few can afford, I’m sure this handy and easy to built watch quartz crystal test circuit will be a great new tester for expanding our electronic tools shack with. And we never can have enough of these tools for testing purposes!

Albert van Bemmelen, Weert, The Netherlands.

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Note: You can read his previous repair article in the below link:

http://jestineyong.com/lenovo-ideapad-330-liquid-damage-repair/

 

Likes(56)Dislikes(3)

15 Comments

  1. Ian Corry

    April 25, 2019 at 11:17 pm

    Excellent article Albert. An easy answer for people needing to check crystals out of the board.

    Likes(2)Dislikes(0)
    • Albert van Bemmelen

      April 26, 2019 at 3:33 pm

      Thanks for your appreciative comment Ian.
      Because we can't just buy a good working tester for these smaller Watch Quartz Crystals it leaves us with no other option than to make one ourselves. And I still wonder why all the cheap working testers and tester Kits available completely fail in testing these smaller Crystals too? As it is so simple to make one on a very small pcb (especially if we use the smd 4060 variant if available).

      Likes(0)Dislikes(0)
  2. Ghashaan

    April 26, 2019 at 1:53 am

    Hi Albert

    I enjoy your articles. This one was way to advanced than for me to understand. Quartz, crystals, oscillators, these are terms beyond my vocabulary. But somehow, it made me finish reading the full article.

    I just thought that this information might turn out to be useful when I really get to learn these stuff firsthand.

    Keep the articles coming. I simply can't wait for the next one. This is not an exaggeration! It's
    keeping me getting back to my inbox now and than to see the next newsletter from Jestin Yong.

    Likes(1)Dislikes(0)
    • Albert van Bemmelen

      April 26, 2019 at 3:05 pm

      I'm glad that you liked the article Ghashaan. If you like this tiny Crystal Tester circuit around the 4060 now there is a good reason to build one. As it won't cost you much and making one is very easy and it surely never fails working! I hope it won't be owning an oscilloscope or the equipment to make one that is holding you back.

      Likes(2)Dislikes(0)
  3. Robert Calk Jr.

    April 26, 2019 at 6:31 am

    I have one of those crystal testers. Mine has a locked MC that won't let you read and save the data.

    Likes(1)Dislikes(0)
    • Albert van Bemmelen

      April 26, 2019 at 2:21 pm

      You mean that the tester with the locked MC is not working because of a bad PIC 16F628A in your Kit, Robert? (that is the PIC that is used in the Kit Quartz tester with boardnumber K159200BSJH 3118-2015 that fails to test those little watch crystals). Because of the extra functions like the integrated frequency counter option, this Kit has some menu options that show up after the Button is pressed. But pressing that Button is not needed to test Crystals that should appear in the display right away after powering up the 5V USB voltage.

      Likes(1)Dislikes(0)
      • Albert van Bemmelen

        April 26, 2019 at 11:04 pm

        I guess you probably tried to copy the PIC and found out that it was copy protected while it was programmed. And in that case you are right there! The TL866 only reads 0000 as data. And the RT809H is incapable in testing these PICs. The RT only sees some 12F family PICs. The guys who sell these with protected PIC programmed Crystal Tester Kits probably are also the same guys from whom I got the dislikes for my article?

        Likes(1)Dislikes(0)
      • Robert Calk Jr.

        April 27, 2019 at 3:27 pm

        Yep, that is the one! I have two of them. One works, but I accidently erased the PIC in the other one. It would not let me read and save the data, but it sure let me erase the data!
        I should have just built a little test jig and used my scope.

        Likes(1)Dislikes(0)
        • Albert van Bemmelen

          April 27, 2019 at 6:11 pm

          Robert, they say that with AVR microcontrollers it is somehow possible to circumvent the activated copy protection flag that prohibits reading and saving the preprogrammed data. But I do not know anything about doing that for PIC microcontrollers. With AVR processors that are locked if the configurations bits are set wrong we no longer can re-program them by their ICSP or ISP connection that is lost afterwards. But that can be overruled by simple reprogram those locked AVR's in a parallel programmer to unlock them. And I believe I've seen some special NE555 circuits that can do the same.

          Likes(1)Dislikes(0)
          • Robert Calk Jr.

            May 9, 2019 at 5:21 am

            Hi Albert,

            I am going to build this circuit that Alan uses in this video so I can test any crystal easily. https://youtu.be/blalAktxFoI

            Likes(0)Dislikes(0)
  4. BEH

    April 26, 2019 at 2:06 pm

    Hi Albert
    Thank you so much of this very comprehensive article about crystals
    cheers
    beh

    Likes(1)Dislikes(0)
    • Albert van Bemmelen

      April 26, 2019 at 11:06 pm

      Thanks Beh! I hope your Opamp Tester now completely functions correctly with all Opamps it can test!

      Likes(0)Dislikes(0)
  5. Parasuraman Subramanian

    April 26, 2019 at 9:37 pm

    Excellent! Very useful article and I learnt something new from you! Testing the resonators outside the circuit is a must for all electronic technicians. Thank you!

    Likes(1)Dislikes(0)
  6. Albert van Bemmelen

    April 27, 2019 at 1:34 pm

    Your kind comments are like the very professional repairs you share always very welcome Parasuraman! Thank You!

    Likes(0)Dislikes(0)
  7. Albert van Bemmelen

    April 30, 2019 at 1:31 pm

    By-the-way: The much larger quartz crystals (about 19.5 x 17 x 7 mm) are much easier to test! For instance a 4433.619 KHz crystal can be checked on the oscillator of a Gate-Dipper. The dip occurs at the oscillating frequency of the crystal. Because these crystals are much larger it only is required to connect one of both crystal pins to the Gate-Dipper circuit. The other pin of the crystal doesn't even have to be attached to anything for this and be left unconnected. I used my Monacor LDM-815 Transistor Dipmeter when I noticed this quite remarkable effect.

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