Author Topic: Service: ETA cal. 7751 Triple Date w/Moonphase & 24h display  (Read 7053 times)


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Service: ETA cal. 7751 Triple Date w/Moonphase & 24h display
« on: April 30, 2015, 12:08:53 AM »
Time to time I try to squeeze in my personal watch projects. This one has most complications I have handled.

Initial state: Rotor is missing and rotor screw remains are stuck in the autowinding bridge.
Date, moonphase and month are not operational.

Immediately after removing the dial we get to the business end of the watch. All the time registers are here. Date driver wheel is emphasized with arrow. The reason not to use date quick set aroung mid night is because of this wheel. This wheel has build-in spring which can snap off if external force is applied. This can happen when the wheel is in right position, which is, of course, around mid night. This has happened in this movement.
Moonphase was not working because dial was little off from the movement, causing moonphase wheel to raise and disengage.

Missing part from the day driver wheel.

Aforementioned part has been scrubbing few parts in the movement, including hour wheel (arrow). This will be replaced.

Rotor screw stuck in the bridge.

Fast forward to full entropy, as the rotor side is identical to 7750.

No service without jewel update. lower 4th was worn. Also convex balance jewels were replaced.

After parts arrive things evolve. After cleaning cycle new mainspring to the barrel.

Keyless works.

Going train.

Running again.

Chrono mechanism almost done. Identical to 7750, so skipping parts in this one.

Watchmakers use alum to dissolve steel from brass plates. I tried this method and it worked beautifully, but the nickel plating suffered for some reason. Even though the bridge is fully operational, I replace it.

From the center post at "7 o'clock" the wheel slips when time is set. (same operation than cannon pinion) I assembled this watch fully once to notice that this part slipped too much, causing watch to jam month change. So I replaced this part too, and did some extra disassembly.

The lever in the lower left side is the date advancing lever.

In the Lower middle section is the 24 hour wheel (4  holes in the wheel).

New hour wheel.

Under the bridge went the new date driver wheel. The "vulnerable" spring visible. Little trick to know in this part of the assembly is to make sure wheels are in correct order. This enables to lower all the way down the day wheel, which advances the month too.

Here the day wheel attached. In the first go I noticed this had been worn too, so this one had to be replaced too!

At Top right the moonphase click and quickset yoke. When the moonphase quickset is advanced, the star wheel turns closer the mechanism and advances moonphase wheel with back-and forth motion.
In low middle the "T" shaped yoke is driven by the date wheel and advances the moonphase wheel as the time goes by.

And then the month wheel click. One intermediate wheel will be put under month wheel.

Ready for the dial! Now everything works!

Some thought needed to be put into the dial replacement. After some thought I got the big picture and I happened to succeed in first try. Most important thing was to make sure that day wheel was in position just about to advance month wheel. In this position time was forwarded until first of the day/date wheels started to move. This was good point to set all the hands to exact midnight.

Hand clearance I like to check before casing  8)

Uusi roottori, laakeri ja "mutteri".
To continue the replacement list: new rotor, bearing and the "nut" to hold these together.

Back in operation. At full wind 300 degree amplitude and six position delta 8 seconds.