Longines moon phase chronograph balance wheel stopped

[cduke]

Hello all

i have a Longines Moonphase chronograph that is less than a few years old and the balance wheel has stopped. Before sending it in for repair, I wanted to ask if anyone had ideas about the problem. The crown on this watch is small, has three positions and can be finicky( hard to move) when moving between positions. Anything to check before boxing it up to the dealer?  Also does anyone know if this is a snap back?

thank you!

[Michael1962]

Photos would assist greatly.

[Nucejoe]

Dose it run any when you shake the watch or advance the hands?     if so , I put the crown in set position, shake to get the oscilator running and advance the hand when running, see if that makes its run as long as you keep pressure on advancing the hands.

Try giving it a full manual wind, listening close you might here a sound of sudden power discarge from the barrel.

Dose it make a difference weather in chrono mode or not? 

Regs

 

[nickelsilver]

If it's the one I'm thinking of it's likely a snap back. As this is a 7751 base (with column wheel), my first guess would be a screw came loose and is blocking the movement. The 7750 calibers are known for working the movement screws loose if they aren't tightened to 80ft/lbs.

[cduke]

40 minutes ago, Nucejoe said:

Dose it run any when you shake the watch or advance the hands?     if so , I put the crown in set position, shake to get the oscilator running and advance the hand when running, see if that makes its run as long as you keep pressure on advancing the hands.

Try giving it a full manual wind, listening close you might here a sound of sudden power discarge from the barrel.

Dose it make a difference weather in chrono mode or not? 

Regs

 

Thanks Joe

My guess is there is a malfunction in the keyless works. Obviously there is a crown position that stops the rotor and it seems to be stuck in that position. No amount of watch movement makes the rotor move.

here are a few pics though not sure how helpful they would be in this problem. The display back looks like it is a snap type but seems unusual for this watch.

[Nucejoe]

9 minutes ago, cduke said:

Thanks Joe

My guess is there is a malfunction in the keyless works. Obviously there is a crown position that stops the rotor and it seems to be stuck in that position. No amount of watch movement makes the rotor move.

Did you mean to say " there is a crown position that stops the oscilator( hack feature) ".

   No crown position should stop the Rotor.

I agree it sure sounds like  the problem is in the keyless, perhaps stuck in hack position. 

 

[cduke]

28 minutes ago, nickelsilver said:

If it's the one I'm thinking of it's likely a snap back. As this is a 7751 base (with column wheel), my first guess would be a screw came loose and is blocking the movement. The 7750 calibers are known for working the movement screws loose if they aren't tightened to 80ft/lbs.

Yes I have heard of this before. I was hesitant to open it up but perhaps I can inspect the rotor through the display back. 
this is a likely scenario as I have read online.  If the crown weren’t difficult to maneuver I would dismiss the other scenario.

[Nucejoe]

If the rotor is stuck, then its a loose screw like Nickelsilver said. 

[nickelsilver]

The hack on these can get out of sorts, but it's pretty rare. But can happen. So that's a possibility. But I've worked on them ex-factory service where 9 out of 10 screws were loose, to the point it was comical except that the customer wasted their money on the factory service.

[cduke]

4 minutes ago, Nucejoe said:

Did you mean to say " there is a crown position that stops the oscilator( hack feature) ".

   No crown position should stop the Rotor.

I agree it sure sounds like  the problem is in the keyless, perhaps stuck in hack position. 

 

Yes that is what I meant to say. But the balance wheel does not move at all.

[Jon]

I've got a 7750 with exactly that problem... the stop lever has got jammed against the balance. You can just see it when you look at the balance from the side

[cduke]

1 minute ago, nickelsilver said:

The hack on these can get out of sorts, but it's pretty rare. But can happen. So that's a possibility. But I've worked on them ex-factory service where 9 out of 10 screws were loose, to the point it was comical except that the customer wasted their money on the factory service.

Display back looks like a snap back to you?

[cduke]

3 minutes ago, Jon said:

I've got a 7750 with exactly that problem... the stop lever has got jammed against the balance. You can just see it when you look at the balance from the side

Have you fixed it? The complications on this watch movement are serious to me.

[Nucejoe]

I bet on one loose screw between the rotor and balance jamming both.

[Jon]

4 minutes ago, cduke said:

Have you fixed it? The complications on this watch movement are serious to me.

Not yet... just took a pic to show. I highlighted the jammed stop lever with a red circle. The keyless work is pretty jammed up as the stop lever has also got caught in the clutch, I believe.

[cduke]

3 minutes ago, Jon said:

Not yet... just took a pic to show. I highlighted the jammed stop lever with a red circle. The keyless work is pretty jammed up as the stop lever has also got caught in the clutch, I believe.

Thanks Jon. Good luck with it.  I thought my watch and I just had a screw loose in common.

[Jon]

2 minutes ago, cduke said:

Thanks Jon. Good luck with it.  I thought my watch and I just had a screw loose in common.

Thanks.... lol

It could very well be a loose screw. Here's a pic of an Oyster Perpetual I worked on recently with a bridge screw jamming up the escape wheel. As @nickelsilversaid, it's almost comical... Almost!

[cduke]

6 minutes ago, Jon said:

Thanks.... lol

It could very well be a loose screw. Here's a pic of an Oyster Perpetual I worked on recently with a bridge screw jamming up the escape wheel. As @nickelsilversaid, it's almost comical... Almost!

Thanks Jon. I appreciate everyone’s help and will post what I find tonight. Great pictures too!

[cduke]

8 hours ago, cduke said:

Thanks Jon. I appreciate everyone’s help and will post what I find tonight. Great pictures too!

Ok, opened the back, balance wheel pivots freely, watch is fully wound, as balance wheel pivots, pallet fork does not advance escapement wheel.  This is apparently the symptom of the problem. On the good side, no loose screw.

[cduke]

13 minutes ago, cduke said:

Ok, opened the back, balance wheel pivots freely, watch is fully wound, as balance wheel pivots, pallet fork does not advance escapement wheel.  This is apparently the symptom of the problem. On the good side, no loose screw.

The pallet fork appears to move and I can only see one pallet jewel which seems fine, the other jewel is obscured by a bridge on top of it. This movement is dense.

[cduke]

26 minutes ago, cduke said:

The pallet fork appears to move and I can only see one pallet jewel which seems fine, the other jewel is obscured by a bridge on top of it. This movement is dense.

It appears as though the balance wheel stud is no properly engaged in the pallet fork. Also the jewels are not synced properly with the escarpment wheel.

only a novice observation....

[Klassiker]

If you are planning to send it for a dealership service anyway, now would be a good time to box it up and send it. There appears to be something broken, which you will not be able to fix. Better safe than sorry.

[cduke]

4 hours ago, Klassiker said:

If you are planning to send it for a dealership service anyway, now would be a good time to box it up and send it. There appears to be something broken, which you will not be able to fix. Better safe than sorry.

Good advice. Thanks

[cduke]

On 4/1/2021 at 8:21 AM, nickelsilver said:

The hack on these can get out of sorts, but it's pretty rare. But can happen. So that's a possibility. But I've worked on them ex-factory service where 9 out of 10 screws were loose, to the point it was comical except that the customer wasted their money on the factory service.

I waited for two weeks for Longines to send service box. Finally, thought to give it a try, popped off the back, removed balance assembly, removed pivot fork and found a big case screw stuck up in the escapement wheel. Removed it, put it all back and it is now running as well as before. Best thing about advice, good to take some and not other.  Thanks again for all the good advice!

[Klassiker]

Well done! Most likely not a case screw through, and now missing from its proper place in the movement.