The ETA 7750 (originally Valjoux) is pretty much the industry standard chronograph and has the full chronograph features plus day and date complications as well as being an automatic calibre.  These are usually a pleasure to work on and this Zeno is no exception.

A lot of parts in these – this container just showing the basic movement parts and I’ve already closed the barrel with a new mainspring.

Valjoux ETA 7750 service and build - parts 1

And this second container has all the chronograph, day/date and automatic complication parts.

Valjoux ETA 7750 service and build - parts 2

With everything clean, the balance jewels are fitted and the balance is mounted on the plate.

Valjoux ETA 7750 service and build - balance fitted

These use the Etachron system for the hairspring mount and adjustments – this is a very nice system and adjustments can be made precisely.

The fitting in red controls the regulator pin gap and firstly that is turned to open the gap.

The one in green is where the hairspring stud is mounted and that is then turned until the hairspring is dead central in the regulator pins.  If it leads to a slightly non concentric hairspring, then the hairspring shape can be adjusted by hand locally between the green and red (it should not be touched anywhere else).

Valjoux ETA 7750 service and build - etachron parts

Then the red fitting is turned to close the pin gap at the regulator to approximately 2 or 3 times the hairspring thickness and, it’s done.

Valjoux ETA 7750 service and build - etachron and regulator pins

Final check that the hairspring is horizontal and parallel to the plate plus that it stays central to the regulator pins over a range of adjustment.

Valjoux ETA 7750 service and build - hairspring

Although I’m only showing about a quarter of the photos in  typical report, each of the parts is checked for cleanliness and wear – some examples as below.  Jewels, bearings and posts in the plate and bridges are reviewed under a microscope.

Valjoux ETA 7750 service and build - jewels and posts inspection

And parts such as the keyless works.

Valjoux ETA 7750 service and build - keyl

Plus the wheels (gears) that run the watch.

And the pivots of the wheels.

After removing the balance temporarily fitted earlier, the keyless works are mounted on the dial side.

Valjoux ETA 7750 service and build - keyless works fitted

Turned over and the train is fitted in place.

Valjoux ETA 7750 service and build - train fitted

Then the main  bridge plus the crown and ratchet wheels.

Valjoux ETA 7750 service and build - crown and ratchet fitted

And the fork and balance so that the basic movement is complete and now runs.  There are some adjustments made here so that all is fine before fitting the complications.

Valjoux ETA 7750 service and build - fork and balance fitted

Next post shows the chronograph and calendar parts being assembled.

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