Kenwood 7150 Dropping Left Channel; ideas?

Hi Guys,

I recently purchased a exceptionally clean looking Kenwood 7150. It had a European plug on it, so I switched it over to 120V and soldered on a U.S. plug. It turned on and worked flawlessly, and sounded great... for about 30 minutes. After that, the left channel starts crackling and buzzing. Eventually, it drops the left channel completely. If you jiggle enough switches, sometimes the left channel will come back for a while, but it is relatively unpredictable. If you put it in Mono mode, it drives all the speakers fine, which I think tells me all of the terminals in the back are fine. I've sprayed some terminal cleaner on the various switches inside; it worked a while afterward, but then started the behavior again. It could have worked again because I cleaned it, but most likely it was simply because it was turned off for a while. What's a logical plan of attack to fixing it? I've been told it might be a speaker protection relay, is this probable? The speaker protection relays are the line of four metal ovals in the center, correct? If this is the problem, how difficult would it be to find the parts and fix it? Is there something else it might be? Thanks in advance. -Ted
Maybe a loose solder joint or perhaps a bad capacitor, assuming all connections are good as you say that they are. A qualified tech would probably have no problem finding the culprit.