> I guess I am wrong about the PIC. It's the TLC5620 that should be replaced isn't it.
>
> Best regards, Karel.

I don't think so. As far as I can see the ADC of the transpose input ignores the lower values. So far I had no time to try it out
with an A-156 from our stock as I'm busy because of the preparations for the Musikmesse in Frankfurt. For the time beeing a simple
patch should solve the problem: add a resistor in the 330k range between the juncture of R9/D3 and +12V. From theory this should add
about 1/12 V to the incoming transpose voltage (provided that I did not make a mistake in my calculation for the resistor value).

Best wishes
Dieter Doepfer