Bought a PO-33 a while back and always had an issue with the input jack. There’s always a bit of fiddling to ease a cable in and I’ve tried many cables and they all have this background hum. It also messes with installing new sounds on it, I can never get past like 20%. I’ve never soldered or done any electro-stuff before so is it worth me trying to fix myself?
if you have a soldering iron, you can retouch jack connection and reflow the solder. sometimes due to vibrations and bending one of the connections come lose while other connection are good. so you can take soldering iron and you just have to remelt soldering connections. touch them with soldering iron and when you see solder melt, remove the iron. repeat this procedure for every connection point. its easy!
how ever i do recommend you to practice reflowing on an old throw away junk before you touch your operator