Strange problem with 2 different A7750 movements

[rionrlty]

I’ve been collecting reps for a long time and have many in my collection that use the A7750 movement.  I’ve had most of the variations used in different brands of watches.  I’ve found them to be fairly reliable, but poorly lubricated from the factory, particularly in the winding train, which has so far been remedied by a partial or full service.  Out of over 25 reps with this movement I’ve only had one that was completely terminal.

 

However I have now run into a very strange situation which is completely new to me, not in one instance, but in two different watches with two different modifications to their A7750 movement.

 

The first one came up last week.  I’ve been working on getting an old style Breitling Blackbird put together.  Although the case is old school, the movement is fresh, taken from the latest generation obtained from Toro.  From the start it had problems, stopping often for no apparent reason.  After a service however it seemed to run fine.  This is the A7750 with the big date modification and the seconds @3. 

 

Whenever I receive a watch I always run the chronograph for day or so just to make sure all of the subdials are registering and resetting properly and this watch performed fine.  A couple of days ago I ran the chronograph for a few hours, to time a sale on an auction site.  When I reset it, all dials returned properly.  An hour or so later however I notice that the hour subdial (although it reset properly) resumed running, as if the chronograph had been restarted, counting off the hours as if it had never been reset although the minute dial remained stationary at zero.

 

A couple of weeks ago I received a Corum Admirals cup (old style) purchased M2M.  It was in near new condition and when tested worked beautifully.  A few hours ago I put it on and noticed that the hour subdial (@6) was not reset to zero, although the minute subdial was stationary in the zero position.  I started and reset it and both dials reset to zero properly, but again the hour subdial resumed counting down.  I then found that I could press reset without starting the Chronograph and the hour subdial would reset to zero.  Under this scenario, for along timing interval, you would have to reset the hour subdial before starting the chronograph.

 

Both of these watches share the same unusual subdial layout with minutes@9, hours@6 and small seconds@3, but the Blackbird has the big date @12 while the Corum has the small date @6 .

 

Has anyone experienced this situation before?  Is this something that’s always been there and I just never noticed it until now?  Can it be remedied? 

 

The Blackbird is in the shop now, but attached is a picture of the Corum about 45minutes after the chronos were reset.  Note the position of the hour counter.

 

 

 

[rionrlty]

UPDATE! On the Corum, after finding that I could reset the hour counter with the chrono reset without starting the chronograph I find now that it stays at zero. So to reset properly after the chronograph was stopped and reset, the reset button would have to be pushed a second time to stop or reset the hour counter. This just gets stranger and stranger.

[Rolexman]

Hour counter brake is faulty or worn down. It is the only plastic part in the entire movement. Common issue on 7750's

[SSTEEL]

Agree with Mark, has a few of these in for repair.

[rionrlty]

Thanks to both Rolexman and SSteel for that.  I will now see if my watch repair knows how to fix it.  Appreciate the advice. 

[kbh]

I have a 7750 with a faulty hour counter brake also. Are repair parts available for this? I've heard A7750 parts are not readily available.

[sneed12]

I have a 7750 with a faulty hour counter brake also. Are repair parts available for this? I've heard A7750 parts are not readily available.

 

Genuine ETA parts will fit. I just did this repair, ETA replacement part fit with no issues. I think have one somewhere if you're looking for one.

[kbh]

That's good to know and thanks for the offer, but I'm not competent enough to take apart chrono movements. I'll let professionals do those and stick to the 3 handed movements.