Mr

[Renaud]

I have a Hamilton Khaki ETO using ETA 251.292 (but doesn't have tenth of a second dial). Recently the watch chronograph has stopped working. It will no longer start and the hands can no longer be reset by pulling the crown and pressing the buttons. I first thought it could have been the battery but then I replaced it and the problem still persists. I downloaded the tech manual for the movement and opened the watch to have a closer look. I found nothing, the coil are in good conditions, the buttons are working fine and the gears are also in good order.

So what could cause the chronograph not to work on this particular movement? All I can think of is an electrical problem (corroded circuit board or a faulty coil, rotor maybe?). Any help would be greatly appreciated as the watch holds sentimental value.

Renaud

[jdm]

Quartz modules can fail in the most unpredictable ways, circuit for this module is GBP 63, complete module 90, (prices + VAT from Cousins UK). Unless you can live without chrono working.

Edited February 21, 2020 by jdm

[yankeedog]

Faulty electrical contact would be my first guess.A quartz watch only operates at 1.5 volts ,it doesn't take much resistance at all to cause problems.While I never worked on that exact movement, I have found that plastic safe electrical contact cleaner may resolve such problems.it may also induce others.

[jdm]

1 minute ago, yankeedog said:

Faulty electrical contact would be my first guess.A quartz watch only operates at 1.5 volts ,it doesn't take much resistance at all to cause problems.

Correct. But reading the OP question we learn that the time section works, but the chrono doesn't, that rules out the a problem with battery contacts, as I suppose you meant to suggest. There are no other surface contacts in the module.
There is a precise flowchart in diagnosing quartz modules. Basic steps are coil continuity and circuit output pulse checks . Attaching here the service sheet in case the OP or anyone else want to go down that route.

 

3568_ETA 251.292.pdf

[watchweasol]

Hi As you will have realised each sub dial has its own coil stator and stepper motor each driven from the circuit block. If all other functions operate ok and the coil resistace of the particular faulty sub dial is ok it could be dirt jamming the stepper, if thats ok then we are looking at the circuit block. As jdm remarked its is sometimes more prudent to change the module. But without dismantling and testing the components including the output of the block hard to be specific.

[yankeedog]

Battery contacts should be fine.As should the contacts actuated by the stem. However since the member has indicated that there is a problem with the pushers not activating the chrono section , could there not be resistance there?

[watchweasol]

Hi   Yankeedog    That is a distinct possibility, One would assume, maybe wrongly, that these basic steps would have been checked, but you are absolutly correct. As the module works on 1.5v  and draws micro amps and dirt/corrosion of any kind can cause a restive surface on any contact which indeed can cause failure and is in some cases,  the battery contacts being the usual suspect. 

[Renaud]

Thanks everyone! I doubt it is battery connection. The watch time fonction works very precisely. I did a thorough inspection of the watch and there seems to be no dirt or connection issues with the coil. I suspected the coils for a while but they show no damage. I also swapped the 30 min coil with the 60 sec coil to see if one might be faulty but nothing. That said I have not checked the resistance of each coil yet (full electrical check base on the technical service diagram). I found no corrosion or connection issue with the movement's components that are pushed by the button.

The fact that it runs on 1.5V and means that little resistance is required for it not work is a good point. Right now I suspect either the circuit board or dirt (but again, the watch is pretty clean). regardless it sounds like I will have to fully strip this thing down, clean all the parts, re-assemble and lubricate...good thing I bought an automatic seiko 5 as a backup watch...

[jdm]

11 hours ago, Renaud said:

Right now I suspect either the circuit board or dirt (but again, the watch is pretty clean)

When the circuit board fails, which is not uncommon, it will be internal to the Integrated Circuit and not visible or repairable. As mentioned before the diagnostic is to check pulse output.

[Renaud]

Alright fellows. I checked for voltage using the 1.5V battery and I do get a pulse on all coils. This is great news as it eliminate the integrated circuit. I removed the battery and checked for coils resistance. Red coil (30 min counter) gave me a resistance within the specs. Green coil (time...which works) gave me proper resistance reading as well. Than when I tested the two other yellow coils (60 second chrono for both hand, its a split chrono), I had no values...which indicates the circuit is pretty much open and the coil is busted.

I put back the battery and to my surprise the time function (the only thing that was working) does not work any more. I did not rechecked the resistance on it as I was too frustrated at that point. so my questions now:

1- Is there any possibilities I busted the coil by checking it for resistance? I mean, there is a current going through it for the multimeter to check it and these things are quite sensitive.

2- Any website where I can buy coils (yellow and green) separately...and coil screws too? The head of one snapped when screwing it down...

Any support is greatly appreciated (moral support too...)

Renaud

[jdm]

7 hours ago, Renaud said:

1- Is there any possibilities I busted the coil by checking it for resistance? I mean, there is a current going through it for the multimeter to check it and these things are quite sensitive.

Yes, must use a low voltage instrument. Normally I mention that, sorry I didn't this time, but the manual does:

Ohmmeter with a test voltage higher than 0.40 V unsuitable, recommended voltage 0.20 V

7 hours ago, Renaud said:

2- Any website where I can buy coils (yellow and green) separately...and coil screws too? The head of one snapped when screwing it down...

This is everybody's question. But there is no secret place for parts, they can be simply unavailable outside the manufacturer network. In your case a new module is, I believe, the best way.

[watchweasol]

Hi from reasearch into the 251 293 ETA movement according to the listings the 251 series have been replaced by the E6 series  the 251 being obsolete so I guess un less you are lucky to find the parts or a NOS 251 series on the web its going to be a replacement module.

As regards breaking the coils whilst checking  its quite possible the coil wire is mico thin and will not take any abuse what so ever. The only other recourse is to remove each individual coil and recheck outside of the movement that way there is no outside influence.