Omega f300Hz service

The Omega f300hz is a tuning fork watch, a technology which preceded quartz. Unfortunately quartz was much cheaper to produce so tuning fork watches were produced for a relatively very short time. I recently acquired one that wasn't working, and so needed to service it. 

The name f300hz comes from the technology; the tuning fork vibrates 300 times a second, which make a visually perfectly smooth sweep. Much smoother than the 5hz seen on most mechanical watches!

As can be seen in the picture above, they have a train more like a mechanical watch, but circuitry (hidden under the top plate) like a quartz.

The watch I had is a Seamaster with a 'cone' case. It's very unusually shaped, making it popular with collectors. It also attaches to the bracelet in an usual way, having no lugs on the case itself.

The first thing to do is remove the top plate or 'oscillator module', which has the electronics and tuning fork attached. The electronics split in half to remove the coils from the fork. To the left of the fork is a bridge covering the index wheel and a second wheel, with a pinion which protrudes though the bridge to gear with the train on the base plate.

The top plate showing the fork and electronics.

An insulated washer helps the two halves maintain a good connection

The two halfs of the electronics

The tuning fork must be removed from the plate and cleaned by hand with rodico. The tops of the arms are magnets which receive impulses from the coils, so, like a rotor in a quartz watch, these will just attract a lot of metallic particles in the cleaning machine!

Next is the base plate and time train - you can see the plastic insulator has some damage from a leaked battery here.

After cleaning comes the fun part: rebuilding and oiling!

Here is the index wheel; approximately 4mm across, with 300 teeth. it's extremely delicate and must be handled with extreme care.

It is pushed around by these ruby-tipped 'pawls'. The one on the right is attached to the fork and so vibrates backward and forwards, pushing the wheel round with a ratchet-like mechanism. The one on the left stops the wheel from going backwards.

The pawls are just as delicate as the index wheel!

The seconds hand is held steady by a steel spring which pushes against a nylon section on the arbor.

The calendar and keyless work. I havent seen keyless work where the yoke is on that side of the stem before.

A friction drive on the 3rd wheel allows the time to be changed.

With the calendar wheel. The wheel is discoloured on two days, where it must have been stopped for a long time.

To regulate the watch, there are two parts on the bottom of the fork. I don't know how these alter the speed that the fork vibrates, but they do! They need to be moved together in opposite directions; inwards for faster, outwards for slower.

And finally... watch that perfect sweep!