7750 what to do when it doesn't autocharge

[GenTLe 1,510]

Hello. so this evening I discover something nice (for tinkerers) so let me share it.

In general when the 7750 stops to autocharge there is one of these 3 problems:

1) the reversing gear is stuck open. This is the most common. The fix itself is easy, but overall it is a pretty difficult task because, once you remove the autowind bridge to reach the reversing wheel to take it out and clean it, you have them to put back in place a number of things and it is all but easy... The process is explained here (this is for a blocked closed one, but the process is the same also for a reversing wheel blocked open);

I don't use the "one dip solution" as Francisco, in general 30m in a bath of isopropyl alcohol is ok to clean it, especially if the alcohol is warm and you leave it for 3/4 minutes into the ultrasonic machine. Then I use the LUBETA 105 to lubricate it, which is the fluid created for that purpose.

 

2) The brass gear of the "ratchet wheel driving wheel" (part nr. 1482) is "munched" (aka missing some teeth). This is also quite typical. To reach that gear you need to remove, other than the autowind bridge, also the bridge below, named chronograph bridge. This is the gear I'm speaking about, in the reps in general it comes like one of these two:

 

In the gen there is in both the upper format or in this one (CousinsUK has this last one):

Now the problem is that you can't directly replace it with a gen ETA/Valjoux one, because the ETA one has the pinions which are larger than the hole in the A7750 jewels where it should go... So you have 2 options:

a) if you have a watchmaker lathe (eheheh...) you can follow this and file down the pinions so that they'll fit in the jewel:

 

b) if you have a stacking set you can remove the damaged gear from the shaft, do the same (without damaging it!)  with a new part from ETA and then reinstall the gen ETA brass wheel onto the asian shaft.

BUT... There is a problem with this.... The gen ETA "ratchet wheel driving wheel" has only 65 teeth. The asian version has 66 teeth (you can also see the difference in the pinion size in this picture):

This means that if you just reinstall all, the contact between this gear and the asian "automatic reduction wheel" (part nr. 1481) will not be proper. Yes, even for 1 single tooth, it will NOT work and once you'll finish to reassemble all the movement, the autowind will not run well and you'll hear bad noise of slipping gears rotating the counterweight/rotor.

The  automatic reduction wheel:

Well. This evening I discovered something good. By replacing the asian "automatic reduction wheel" with a genuine ETA one, all works well! 

So remember, whenever you replace the "ratchet wheel driving wheel" with an ETA one, regardless you do that by thinning the pivot of the shaft, or by replacing the damaged brass wheel with an ETA one on the asian shaft, also replace the "automatic reduction wheel", which is a direct fit, and all will work well!

 

3) the steel gear of the "ratchet wheel driving wheel" (which is part of the shaft) is munched. In this case you can only follow the 2)a) upper or using a donor asian 7750 to take the part. In any case, also with the 2)a) upper, remember that in the moment you fit an ETA ratchet wheel driving wheel into an asian 7750, you also need to replace the automatic reduction wheel.

 

Cheers, GenTLe

 

[GingerApple 7,306]

For fuck's sake Gentle, I was literally just about to post an identical thread....