Omega 720Hz Megasonic running too fast

[Gacello]

Hello folks,

I am fighting an issue here with a cal. 1220 Omega that gains more than 30s daily. The resonator shows correct frequency on a tester but still the watch gains considerably. It seems to be occasionally "double indexing" just like an Accutron not properly phased. Anyone here who had the same problem before and found a solution other than just changing the entire resonator? Even only an explanation for the cause of this effect would be much appreciated!

Thank you!

[uscjake87]

I would say that omegaforums is a better resource (because this is an accutron sub-forum), but you probably won't get good answers there either. The megasonic 720 is a rather finicky watch and parts are non-existent for them. I recommend you email these questions to these watchmakers, but they do frequent the forums and might see this post.

Rob Berkavicious

Chris Radek

[Chris Radek]

Does it run right if you put a mercury battery in it, or an accucell, or run it at reduced amplitude with the accutron test set or similar?

[Gacello]

Chris, I had the same thought and will check what happens on reduced voltage. Will post as soon as I have results.

[Gacello]

Took a while until I was able to get back on this particular watch. I did test with lower voltage now and it turns out that the double indexing reduces with reduced voltage. BUT I need to go down all the way to 1.1V to get it close to correct rate. Reducing the voltage that far with a z-diode is not an option as the movement will not even self-start anymore. I had more input from Rob and Chris on this issue and it looks as if it is rather common for the 720hz Magasonic to double index. Guess I need a new fork...

[Chris Radek]

Can you see if the oil is good in the micromotor? It doesn't work as it is, there'd be no harm in trying to open it up and service it. It sure would be nice to be able to adjust the finger tension and the spacing of the bumpers wouldn't it? But if we assume those haven't changed (I don't know if it's correct to assume this) and we assume the fork and its magnets haven't changed (likewise), then it's the state of the oil that has changed, which would be very unsurprising.

[Gacello]

Chris, would you consider the viscosity of the oil to be changed? I can see there is no air inside as I have seen on faulty ones before so I did not assume any issue there. Have you opened the motor before and if so, did you heat it in order to loosen the glass cover? Was it safe to do that without also loosening the glue that fixes the components inside the motor?

[Chris Radek]

I haven't done it, I'm only guessing. I have some work coming up on two of them, and might try it if I have a dud, which seems pretty likely.

If the spacing of the bumpers hasn't changed, it really seems like it could be the oil viscosity. I suppose the oil is there for damping more than lubrication, and it might be sensitive to viscosity. I think drilling a hole, flushing and refilling, and then plugging it might be easier than removing the glass, but who knows without trying?

I have no spare parts to play with except one dud coil, right now.

[Gacello]

Ok, here's an update with more findings regarding this 720hz Omega running fast. Man, this is a tough one...

Initial problem: watch movement cleaned and assembled, then running fast at about +15s/hour.

my tests:

installed a NOS fork - watch runs ok
reinstalled original fork (F1) and dropped voltage - rate goes down but requires large drop to 1.0-1.1V to actually run correctly
installed NOS electronic unit together with original fork (F1) - watch runs fast
got another used fork (F2) that worked ok in a donor movement - watch runs fast
changed F2 over to a different test movement (M2) of mine - test movement runs ok with F2
installed F2 + 2nd&3rd wheel (large magnetic wheels) from M2 into problem watch - watch runs fast
additionally installed 1st wheel (small magnetic pinion) from M2 into problem watch - watch runs fast
changed F2 to NOS fork again - watch runs ok

Any hints highly appreciated!

[watchabit]

Leave NOS fork in...

Sorry, couldnt resist. Enjoying the thread though, I didn't know about these movements until now.