Sq80 no sound no power mysteriously manifested

I bought a used sq80 from GC & it worked with sound output. I have another s80 so I just stood this up on it’s side and didn’t play it for 2 months. My horror was now it won’t power up or sound. I did take a volt meter & it’s getting voltage and the fuses are intact. I suspect it may be the power supply board but I don’t know how to test the leads to be positive before I buy a replacement power supply board. Thank you in advance & happy holidays to every synth player on this site.

This could be a power supply issue, or it could be a display issue. The next step is to turn the power on and then press buttons on the top panel. When you press random buttons, do any characters show up in the display?

If so, there is a communications problem between the main board and the display. If nothing shows up, it is likely a power supply issue. So try this, let us know the results, and then we’ll go from there.

Hi there,
I do have a SQ80 in service, problems in power supply due to the former repair man, shorted -12V stab IC circuit (forgotten plastic isolater-ring in the attaching screw), the machine worked once, one time perfect, played sounds, I shutted it of and again on, now no startup anymore, power supply is working fine, all voltages are correct, all new fuses installed, only with variac slow voltage raise, the display sometimes gives strange symbols, but no action furthermore, reset with full ac voltage, never a startup again of the machine. The only chip that heats up is the main microprocessor HITACHI HD68B09E, all the other chips remain cold! Bad processor? Thanks for reactions, I hope. Sincere greetings , Luc from Belgium.