Accidentally touched my PO-12 with 9V power output and now it behaves strangely

So yeah, I accidentally touched my PO-12 mid-jam with plugged-out 9V output cable. PO-12 went off and on, and now it reboots every time I press something.

I replaced the batteries, turned it off/on again, but it shows same behaviour: PO-12 boots, I press one button and it goes off again.

Any advice on how to fix that? I'm not ready to let it go just yet :(