f300 Cal 1250 diagnostic question for watchmakers and tuning fork aficionados

GregH · Feb 15, 2017

Hi all;
I appreciate in advance any help on a diagnostic question on my Omega f300 Cal 1250, which appears to be misbehaving. Clearly it needs a service, but I was hoping someone might have thoughts on the diagnosis. Here's the issue. Lying flat, face up, the watch appears to run and keep time fine. As soon as I put it on my wrist or in a case for transport, it speeds up dramatically. For instance, today, from 8 am to 6 pm it ran fine sitting on my desk. I strapped it on my wrist at 6 pm and when I got home at 9:30 pm, the watch read 10:15 pm. Lying flat again, it slows back down and appears to keep time normally again. Any idea what might be causing this?
Thanks for any ideas.
Greg.

tyrantlizardrex · Feb 16, 2017

Worth checking it has a correct, fresh battery in for the cheapest possible fix. 👍

Renata 344

Deafboy · Feb 16, 2017

I own one of those excellent watches and, although not an expert, may be able offer an explanation. A tiny jeweled pawl attached to the tuning fork moves a teethed wheel one tooth at time for each fore-and-aft motion of the tuning fork. This happens at a rate of 300 times a second, i.e. the natural frequency of oscillation of the tuning fork. This toothed wheel is the first wheel of the train that drives the hands. What is happening in your case the pawl occasionally jumps over not one but two teeth, which makes the watch run fast. The watch was designed for batteries of the 1970's which had a lower voltage than today's batteries. A modern battery will cause the tuning fork's amplitude of motion to be too great and can cause the pawl to jump over extra teeth. In your case, the motion of the tuning fork is at the threshold of jumping teeth and the orientation of the watch causes it to run normal or fast.

Whatever the cause, it should be an easy adjustment for a watchmaker specialized in these movements.

The upper pawl links the tuning fork (not shown) to the teethed wheel (on the right).

GregH · Feb 16, 2017

Thanks @tyrantlizardrex and @Deafboy ! You're both fantastic and I have some guidance when I bring the watch for service. Hopefully something that can be regulated simply. Crossing fingers!