Rockford Fosgate 550x

[irwintan27]

Hey guys, Aloha!, new member here. Name is Irwin and from Hawaii.

I recently acquired a Rockford Fosgate 550x, 4 Channel Amp from craigslist and out of the 4 channels, only the 2 front channel works. The 2 rear channels will produce crackling, full of static and has a very faint noise. Switched the speakers front to back and they both work with crystal clear sound. Speakers are JBL 600 and 602c, no subwoofer. I opened the amp but didnt see any burned transistor of any sort... Switch the RCA and the same problem occurs... Can anyone help me? I tried checking the transistor with a voltmeter but dont know exactly if I'm doing it right. I believe the transistor are LM317T...

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[Spooney 10+ year member]

The LM317T is not a transistor. That part is a voltage regulator. If you can get me a good quality pic of the inside of the amp I can help you at least find the right transistors to check. Have you checked to see if those rca inputs for the bad channel are actually connected to the board or maybe perhaps they have snapped off over time. It would be nice if you could verify that audio was making it past the rca inputs and into the preamp circuit of the amp. I have seen a few amps in my time with weak/distorted output that was caused by some bad caps in the audio input chain as well.

 

[irwintan27]

I dont have a picture right now but here's a video by someone