You need to talk to Ramon... he knows what's up with these bad boys electronically.
As for myself, all I can tell you is that one of the five fuseable resistors on mine had gone bad, which is why my deck was not working. And Ramon pretty much called that out in advance as this is apparently a common issue for the M90.
Here was the culprit on mine:
I had a tech in Tampa do the work for me. He charged me $66 and swapped out all five of the resistors as they were all the same kind. He also calibrated the deck (azimuth adjust & speed adjust) and is plays fantastic now. Best $66 I ever spent!