After rebuilding a 600 that I bought from a pawn shop, I can tell you, these are not easy amps to work on. They are very difficult to get into and replace all of the electrolytics. You will need to find someone with specific experience rebuilding these amps. They are worthy of a rebuild. Hopjohn is the expert here on these amps, but I don't think he is a guy in the business of repairing. Search for his instruction and parts suggestions. If you find someone with the dedication to complete this job it is probably going to be expensive. A lot of hours involved here. Oh, after listening to this amp with a QUALITY input driving a variety of speakers, I think it is right up there as one of the best I have ever had in my systems.