EJ's.....need some help-

I helped out a fellow member by installing a set of Phoenix Gold components, a Line-Level Converter, and an Audiobahn A2002 amp (under driver's seat). He has run into some problems as of late.

Every now and then the passenger's speakers will just cut out. This only happens when the RCA's are plugged in ALL the way. As you back them out slowly, the channel comes and goes. I know it is not the RCA's (I have an extra set of Rockford Fosgate wires sitting around, and I swapped them with the same results). There is no problem with power, as my multimeter reads ~14v when alternator is running. Ground is solid (12mm seat bolt sanded down).

I believe that there is either something faulty with his amp, or the LOC. I am going to pull my Infinity 2-CH amp on thursday and see if when plugged into his car it works or not. If it works, his amp is obviously bad. My (other) buddy told me that there might be a bad solder connection between the RCA terminal and the motherboard of the amp. (He has been in car audio and RC cars for a while, so he is VERY fimiliar with soldering ) Would it be that easy to fix such a problem? (I dont think he can return it, as it was from an unauthorized dealer).

I am just trying to help a fellow member out....

Thanks

John