Fixing Amp - No Ideas

[johnscustomtint]

I'm new to fixing amplifiers so forgive me if I don't know what I'm talking about. I like car audio and electronics and thought fixing amps could be an interesting hobby. I searched and read quite a few posts, but couldn't find this problem (probably too simple).

Anyway I have a cheap amp that I am starting out with. It is a Nitro BMW 2 channel 800 watt (yeah right). It was in protect mode and I ended up testing and replacing all the output transistors (one was shorted) and now it kind of work. One channel is fine but the other fades out after a few seconds of playing. I replaced the output transistors again (seemed like a good idea) but nothing happened different. Music will play out of it for a few seconds, then a second of static, then nothing. It will also play for a half-second when the remote is removed. The longer I leave it off, the longer it will play when I turn it back on (maximum of 5 seconds). I was thinking a capacitor because the longer its off the longer it will play (capacitor discharging?) but I don't really know where to look. Nothing is obvious like cracks in the board and nothing responds to me poking at it. Any ideas?

 

[lineup]

put a couple of multimeters across voltage supply lines
and see if you can get any information

measure and then see if your logic can get closer to source of problem

 

[jaycee]

At a guess there is some VI limiter circuit with damaged parts. Look for some small signal transistors that clamp the bases of the driver transistors via small signal diodes.