Thank you Paul,

I made a few tests this morning:

@ Z59 (ADC0804) I can see pulses changing while I play the keys, this should be enough to exclude a fail in the CPU, I believe.
+5v Digital= It was 5.09v, I set it back to 5.00v. If I try LFD3, all LEDs are on, a couple have a bit less brillance but something minimal. I noticed after a second the LF function is disengaged without my action.
Ref +5v= It was 5.01v
Nominal DC lvl= it was a bit out, fixed
ADC Range= this time it worked, turning the LED on
DAC Null= Fixed
After all this and a total reset, loading a scratch patch, I cannot hear any sound