CWC G10 Fatboy1980 Military Watch ESA 536.121- Service

Something a little different today on the blog as I predominantly featured mechanical watches in the past. This article is about the service of a British Military Watch, the CWC G10. This watch was issued to a member of the British military in 1980. It is powered by the Quartz movement ESA 536.121. This particular model is the first incarnation of the many G10 versions, and is nicknamed “fatboy” due to its thicker case profile in comparison to subsequent models.

As you can tell from the photo below the watch does certainly look like it has hard a hard life!

CWC W10 1980


I start by opening the watch, there is a battery inside, thankfully no apparent leak. I try the watch with a new battery, but quite predictably it is not working. However after testing the watch on my quartz diagnostic machine, I detect a pulse. This is good news, as the circuit seems to be functioning, and the issue is likely to be mechanical rather than electronic.


The movement is removed from the case.CWC Fatboy


I start by stripping down the movement.

ESA 536.121


Nearly there, here you can see the wheel train exposed, with the stepper motor on the left.


The movement is fully stripped down.CWC W10 Service


The parts are cleaned in the cleaning machine, and inspected. All parts are in good condition. There is typically a lot less wear in a quartz watch compared to mechanical equivalents, as the train wheels are subjected to much lower torque values.ESA 536.121 service


The case parts are cleaned in the ultrasonic tank.


I can start re-assembling the movement.


Finishing here with the integrated circuit.


A new battery is fitted, and the watch is ticking again very nicely. I check the value of the current drawn  by the movement stem in (whole movement functioning) and stem out (module only) . The continuity of the coil is also checked, and all is well. The case is spotlessly clean, but you can see there are a few pitting marks caused by corrosion over the years. A gasket is fitted prior to fitting the caseback.


Finally a new crystal and NATO strap are fitted, what a transformation!CWC W10 Fatboy Service

12 Replies to “CWC G10 Fatboy1980 Military Watch ESA 536.121- Service”

  1. Hi Oliver I have a G10 Fat Boy that has stopped working and the winder also come out. Is this some thing you could fix.


    1. Hi Peter, thank you very much for getting in touch. Yes, it is very likely to be something I can fix, I will send you an email with estimate.
      Best regards

  2. I have a Heuer watch with the same movement do you know if it’s possible to get replacement circuits and also where can I get the quartz tested ?

    1. Hi Colin
      Unfortunately replacement modules for this movement are very difficult to get hold of.
      With regards to testing, any competent watchmaker who is working on Quartz watches should be able to do that for you. I can help you with this as part of a service of the watch, so do not hesitate to get in touch by email if this is of interest.
      Many thanks, Olivier

  3. Hi Oliver
    Do you know where I can get a replacment battery cover for 1980 fat boy?


    1. Hi Karl
      Unfortunately these are very hard to find, the best way would be to source a suitable donor watch.
      Good luck with your project!
      Best regards

  4. Hi Oliver ,
    Stunning. Work !
    I also have a early 90’s G10 which has stopped working please could you help ?

  5. Hi Olivier .
    I’ve got a couple of ETA 536.121 movements that need servicing . Could you get in touch to quote for this ?
    Kind Regards

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