Thanks for the tip!
To tell you the truth, I've never programmed an FM synthesizer before, so I'd need a serious learning curve :) With the oscilloscope, I thought that at least I could find out if the DAC is faulty. I looked at the signals on the good DX7S motherboard during the test tone generation (880Hz- same test program here) and even without a logic analyser you can see pretty well what is happening around the DAC (DA2-16 legs and SH1/2), you can definitely spot if there is a problem here. Of course, the communication between EGM - OPS and CPU is a whole other problem unfortunately.
