This particular Bulova Accutron was sent to me by Constantine from NY State together with a batch of other watches. It is his father’s watch, and he would like to see it working again. His father’s name is even engraved on the back.
The watch is pretty dirty, and the bracelet will need an heavy-duty ammonia treatment!
This is an N6, so it dates from 1976. Not sure if the 7-6 stamped with ink into the watch back is a coincidence or not.
First look at the movement. The battery is empty and the battery clamp is taken off.
I take the movement out of the case and start taking it apart.
This is a day/date model.
The winding and date/day mechanism is now visible.
On the right side of the cannon pinion is the bridge holding the jewel for the fourth wheel – this is the only jewel that isn’t capped – this explains the odd count of 15 jewels.
Now I turn my attention to the top plate.
The wheels. The smallest wheel at the top is the index wheel – it has 320 teeth!
With the wheel bridge and wheels removed, you can clearly see the tuning fork in the middle.
The tuning fork. It swings at 360Hz, thus moving the index finger 360 times into the index wheel, which has 320 teeth. So the index wheel turns 1 1/8 or a turn every second.
The two coils. The coil on the left – called the component coil – has actually two different windings. One is excited by the magnet swinging in and out of the coil, and it drives the transistor, which in turn powers the second coil and the coil on the right, which moves the tuning fork. The electronic circuit consists of a transistor, a resistor and a capacitor. The capacitor provides the initial pulling / pushing oscillation needed to start up the tuning fork.
The parts are ready for cleaning.
Now I test the components and find out that the capacitor is broken. That’s why the watch didn’t work – without the capacitor, the watch doesn’t start swinging. The coils are alright. I have a replacement component coil that I bought on eBay the other day (with this watch in mind) and I will use that.
I will of course keep the other component coil and replace the capacitor next time I need a coil.
To test the electronics, I put the watch back together with the new component coil and a new battery – I haven’t put the wheels in, as I will have to take the watch apart again.
That looks good!
But the fork is hardly swinging, and I have to get very close to hear even the slightest hum. So there is something else wrong.
With a 20x loupe, I see that the fork ever so lightly touches the plate on the left arm of the fork. The fork position can be adjusted using different washers, and I correct the position so that it is free of the plate.
Now it’s humming nicely, and I can put the watch back together.
After a day in the ammonia, the bracelet is clean.
Starting to put the watch back together.
After the tuning fork and coils, the wheels are put into position. The jewels have to be oiled first, as they are all capped.
Having oiled the capped jewels in the bridge, I mount the bridge and nudge the wheels into the jewels. This is a bit tricky. You have to turn the pawl and index finger away from the index wheel when doing that to avoid damage to the fingers. Once the wheels and bridge are in place and the bridge is screwed down, the fingers have to be adjusted using a microscope. As soon as that’s done, the watch starts turning.
Now I turn my attention to the bottom plate, starting with the time setting assembly and the date/day assembly.
Bottom plate finished.
As the watch case is pretty dirty as well, I give it a bit of an ammonia bath as well.
Having mounted the dial and hands, I put the movement back into its case.
Great dial – so 70s!
Hmmmmmmmmmmmmmmmmmmmmmmmmmm @ 360Hz 😉
I won’t put the bracelet back on yet, as I have to adjust the watch first. I set it to the exact time and put it on the bench. Tomorrow, I can calculate how slow or fast it’s running and correct it.