A Harman/Kardon AVR 645 repair has been a hobby of mine for the past several years. My latest attempt involved the purchase of a DOA unit for part swapping and testing. The original AVR would power up then shut down after a few seconds. I completely tore down both units, found a couple of bad components and reassembled one of them. Same issue, no speakers connected. After extensive research I found a repair document from Harman/Kardon that explains the protection circuit in fantastic detail and provides specific test points for each fault (power, DC detection, overload & power) and the voltage...