I found the owners brochure; no clue regarding troubleshooting. Posted to the AVS forum which has some additional info and corrections. This is an EP350 v2. not the EP175.

revised post:

about 1 -2 minutes after turning on sub, it switches from on (green light) to standby (red light). If I remove the input RCA cable, it switches back to "on" for 1 -2 minutes and will output a test tone and then switch back to standby. I noticed that the RCA input port is _slightly_ "wobbly" - not really loose but it will rock back and forth slightly if pushed. In comparison, the output port is solid. I removed the back panel and looked at the port from inside and could not see anything out of the ordinary, eg loose wires, burned component...

Does anyone have any ideas?

This is an Axiom EP350 v2 sub purchased about 12 years ago.

Thanks for any tips.