Some while ago I got broken power amplifier WS503 polish factory Unitra. On the beggining I thought replacing main fuse will be all I need to do. It turned out that really fuse was burnt, but from speakers protection circuit. When I opened a case and spent some time with multimeter I realized that also one power circuits was broken down. I started work and after eight evenings, everything was fixed. Generally whole device looked as really devastated. I think someone used that equipment somewhere outdoor and played music on whole power for some long time. I found many sympthoms telling about overheating. Also rusted screws can confirm this theory. No matter what, the most important thing is that it works and now my neighbours and I can listen to some good music ;).