You most likely blew one or both channels or if your lucky you just vibrated a resistor off the board.
Almost every 4000.1 that I sold from my shop needed servicing at one point or another.
Also depending on where it originally came from it could have been a refurb. Whenever we sent in an amp for warranty they would send back a brand new one. And where do you think those amps that were sent in ended up, yup on
ebay or some other closeout site.
Also the RCA inputs brake real easy on a lot of the Autoteks
Hope that helps.