Repairing when you manually wind and the rotor spins (7750)

[onzenuub 362]

Originally from Francisco:

The problem we are going to repair seems to be quite common in the A7750 movement. As the video shows, when you manually wind the movement, the rotor spins:

The majority of times the cause of this problems is the “revising wheelâ€. This wheel, as show later, is a double gear. Some times these gears are gummed. The solution is, of course, cleaning the wheel. Other times cleaning is not enough to solve the problem and the reversing wheel has to be replaced. Movements with this problem tend to show low power reserve and may be not reliable.

 

If it was only a cleaning task, this will be an easy repair. However, it is quite complicated because assembling some pieces is rather difficult. This tuto has the objective of explaining with detail how to assembly this part of the A7750. Knowing how to do it, you can solve some issues of this movement, as future tutos will show. However, some skills and experience are need it.

 

We are going to repair the HBB show on the video. First steps are removing the case back and the rotor. Red arrow shows a hammer spring that has to be disassembled. You have to push out the spring , fasten it where the arrow shows and the lift it up. Next step is to remove the spring shown by the green arrow.

 

Next picture shows the position of the hammer spring after pushing it out and lifting it up. It is resting on the plate.

 

 

The movement after removing both springs.

 

 

Next step is to remove the 3 screws that fasten the automatic device bridge:

 

 

And the bridge is removed. Be very careful, do not move it horizontally. This is what you will see:

 

 

Wheel A is the root of the problem (majority of times). We must clean it. If it does not work… get a spare for it. However, the swiss spare needs modification, so better use a reversing wheel form another Asian.

 

Of course the best approach is to disassembly and to clean the whole movement (service). However, we focus here only in trying to solve the problem shown on the video. In this case we are going to clean pieces A, B and C. Piece A is part of the auto winding system. Piece C…. I did clean it because I found it very dirty. It is a hammer that resets seconds and minute counters. Nothing to do with auto winding.

 

 

The previous picture shows the wheel A. As seen, it has to faces, two gears. One connects to the rotor. In one way both gears must rotate independently. If not, we have the issue we want to repair. In some movements the dirty gums both faces.

 

We have to assure a good cleaning procedure. I used a two steps cleaning. First one, using One Dip. If you do not have it, move to ultrasonic cleaning. One Dip is a very powerful grease remover (and very toxic) employed in watchmaking.

 

 

The reversing wheel is immersed in the One Dip bottle. Shake it very gently and leave it for at least 10 minutes.

 

Next step is ultrasonic cleaning. I am not going to explain the procedure.

 

Now it is time to re-assembly the movement. Take into account that this is very difficult. However, I am going to explain with details the steps to follow.

 

In first place, check that the oscillating pinion is in its correct place. There is a chance that you move it when removing the bridge. Next picture shows where you have to look.

 

 

The correct position of the oscillating pinion: It has a very small pin that has to centred on the hole of the above piece (the clutch). Be careful, sometime seems well assembled, but it is not. You have to see the pin through the hole.

 

If it is not well assembled, you have to use a small screwdriver in one hand to lift the clutch up and the tweezers in the other hand to assemble it correctly. Next video shows how to do it (video shows another watch, for a coming tuto)

 

As we have cleaned 3 pieces, now we have to oil them when assembling. Follows the oil chart of this part of the 7750 movement.

 

Gear B is assembled and oiled.

 

 

Gear A is oiled and assembled.

 

 

 

Very important. When assembling piece A (reversing wheel) you have to check that one spring connects correctly with the down gear of the reversing wheel. Red arrow shows how this spring bar connects correctly.

 

 

Next step is assembling piece C.

 

Will be in part two.

[onzenuub 362]

 

The hammer C has the function of resetting seconds and minute counters pushing the cams of both counters. Therefore, assembly the hammer as shown in the photo 8red circles).

 

Next step is oiling this hammer. The hammer is separated a bit to the right to help the oiling task.

 

 

 

Now it is time of assembling the bridge. You have to do it very precisely. Fist time you will fail…and the second time…. and…. …. Some pieces will change their position in your tries. Be patient. This is so difficult that the bridge has to windows (green circles) to check that everything under the bridge is correct. One window shows the oscillating pinion and the other one the reversing wheel (to check the spring bar position).

 

 

Next photo shows a problem that surely you will have. The pin of the minute counter does not fit the jewel of the bridge.

 

 

This is the way I solve it (just my approach). I screw the two upper screws of the bridge. Check that the reversing wheel rotates.

 

Then I try to fit the pin of the minute counter. I screw a bit the third screw of the bridge…I try to fit the pin… I screw more…

 

 

This is the final result. Check it!

 

 

OK. We have finished probably the most challenging part of assembling the 7750. Now it is time to assembly the spring shown by the red arrow.

 

 

And the other spring.

 

 

Now check that the chrono functions work properly. If so, screw the rotor and the check if the problem shown in the video is solved. If not, change the reversing wheel.

 

 

 

Thanks for reading,

[SSTEEL 0]

Superb, thanks for reposting mate.

[MDK 7]

keeping the oscillating pinion in place during the rest of the assembly, especially the bridge , is one of the most difficult things I have done