Akai ax73 repair / clock speed issue

Synth Repair
1

Hi! I recently picked up a well-used AX73 and I’m working on fixing it up. Initially it was just producing terrible noise but now after some cleaning, reconnecting connectors, reseating and replacing some voice chips I have it making sound again. The issue now appears to me to be with the clock speed of the synth? All of the patches seem to be much lower in pitch than they should be (lower keys are almost inaudible), the voices are all significantly detuned and lfos are super slow making the patches sound odd.

The operation of the display seems to work ok, I can cycle through presets and banks, adjust parameters and volume, etc. I see a 12mhz crystal on the cpu board and I can see it outputting a sinewave, it appears to be cycling once very 100ns or so. I haven’t had much luck finding a service manual for the ax73, but have been referencing the one for the ax60 which is similar.

Any thoughts on what I should consider next for diagnosis would be much appreciated. I’m not sure if the crystal itself is bad or if there are components dividing it, etc, which would be to blame. I can send shots of waveforms, or record audio if that would help. I don’t have a working ax73 for comparison but I’m pretty sure it’s not correct as it is lol.

Thanks!
Roland

2

Quick update - I took another look and I think the crystal appears to be operating at 12mhz. There are two transistors that are in between it and the cpu, I’m wondering if these may be the issue. When the signal comes out of the second it still appears to be close to the same timing but the waveform is no longer a simple sine, it is quite distorted, with the rise slower than the fall. I’m not sure what their purpose is exactly or if this is expected, let me know your thoughts.