Derby & Schaldenbrand Cal.ETA.7751 base
Symptoms: Poor accuracy (delay) / Moon phase malfunction
Repair contents: Overhaul, spring and gasket replacement, case cleaning
Repair cost: 33,000 yen
I took it apart. It is a movement based on ETA 7751, and is a model with a chronograph, triple calendar, and moon phase. I think this is the most common movement for Tri-Cal Moon.
Assemble. The back of the scale is transparent, so there are decorations on the base plate and the receiving plate.
In the case of chronographs, there are push buttons in addition to the crown, so they are not very waterproof. Therefore, moisture easily gets in, and the parts rust and discolor. This one is also in good condition.
The back side. The photo was taken before disassembly, so some parts are dirty.
There was a problem with the moon phase not being transmitted, so we will be modifying the parts.
Adjust the moon phase so that it is linked to the time. The moon phase advances at a different time than the date and day of the week, so care must be taken when fast-forwarding. If the moon phase and time are interlocked, fast-forwarding the time can cause parts to wear out or, in the worst case, chip.
The moon phase is visible at the 6 o'clock position. While other parts are available, the moon phase disc may be an original design, so if a tooth on the disc is chipped, it may need to be repaired by the manufacturer.
We will casing and run a running test. Although it is a chronograph, it is a model without a second hand, so to check the accuracy, it is necessary to operate the chronograph and test it. I am sometimes asked whether it is better to operate the chronograph from time to time, but I think either is fine. One thing to note is that it is better not to flyback as much as possible for models with flyback. I just had an overhaul of a Breguet flyback model, so I will write about it again.