I dropped my amp (kicker zx750.1) off to get repaired. I get power and the amp does not go into protect mode but i get no sound output. The repair tech had no problems with it and after 1 1/2 hours of continuous play, it never cut out on him. He took me in the back to show me that it was working. The only difference was he had the negative part on the rca's going to the input soldered to a ground. When he unhooked the rca ground the output would cut out.
Now here is the part im not sure about because i don't know if he was trying to drum up more business or not. He told me i couldn't ground the rca's with a stock hu as it would damage the hu. I have a 2007 mazdaspeed3 with the stock stereo. Also, the amp was in the car for about a year working perfectly with no ground to the rca's.