Yamaha PSS-480 turns on but no sound.
I bought a cheap Yamaha PSS 480 on shopgoodwill and it didn’t come with a power supply. I grabbed one I had laying around and that’s when I found out about different polarity power supplies! The Yamaha required a center positive but I used a center negative and think I fried some type of polarity protection diode or something.
Looking around, I realized that’s probably the case and I removed the zener diode (no idea but probably made it worse!) and put in C batteries. It powered up but no sound except for the speakers pop when I turn on the power and they fizzle. Poking around in the AM board I can produce loud pops from the speakers. Still no sound from the keys. The display works and you can change settings.
The capacitors on the AM board seem to be okay, at least none are open circuits when I read with the multimeter. I attempted to trace power throughout and in getting voltage across the board. I looked up some of the ICs and they seem to be getting the correct voltages but I could also be misreading that as that’s a new skill for me.
Any ideas before I pass this thing back to Goodwill for parts? I’m in Austin but is this even worth taking to the Syntaur shop down south?