New on forum. Have seen some older posts on similar or same problem, but didn't see any conclusions.
Unit powers on, but no characteristic 'thump' when relay kicks in. No audible sound from speakers at all - nothing.
Unit quit working without fanfare - just stopped. Had it since new in 1992/93, but not used really hard until recently, when I acquired a receiver with the lossless codecs.
Backplane inside shows no damage to individual components - nothing obviously smoked or toasted. Have a schematic, but have not measured any voltages because I don't know what to measure or what to expect.
Have ordered but not yet received new STK4050V amp.