Yamaha YC 25D detuned

[HansMeier]

Hello dear organ fans,

We have acquired a Yamaha YC-25D for our studio. Unfortunately, the UPS transport didn't do the organ much good. One control knob was off and a key was broken. We've fixed that by now. The last problem is now the tuning. The notes D, D#, and E are out of tune. And this is the case across all octaves, as well as the upper manual, lower manual, and bass.

We have researched extensively but haven't found anything on where or how to adjust the tuning.

Maybe someone knows something

Thanks and best regards,
Hans

[Hugh Robjohns]

Like most instruments of that era, the organ has a set of 12 master oscillators which generate the top octave frequencies. These are then divided down to provide all the lower octave notes.

Thats why all the same notes are out of tune in all the octaves.

I'd start by getting hold of the service manuals. You could start here:

https://www.combo-organ.com/Schematics/

They suggest using the YC45 service manual as that organ is very similar, in combination with a supplementary yc25 manual which highlights any differences.

Fundamentally, though, you need to find the master oscillator circuit boards which are at one end of the rack inside the organ. Then identify the oscillators for each note.

I believe tuning is achieved by tweaking the movable core inside a small inductor on each board. You will need an appropriate non-conductive tool to do that.

I suspect the organ was dropped and the shock has caused the cores to move in some boards.