I repaired this Sony STR-DE915 receiver which had no output on any of the channels even though the dc output was normal and the speaker relays were clicking on. The culprits were two AC muting transistors, Q503 and Q512, which are activated from the CPU.
I tested the analogue portion of the receiver and that was ok. Then I hooked up a Marantz DV6200 DVD player to it and it worked fine with an optical cable hooked up to it but when switching the input to a standard coax cable as well as switching the input mode to "Digital (AC-3 RF)" there was no sound. The digital coax jack on the back is labeled, "LD/DVD IN, AC-3 RF." Is this not compatible with the current Dolby digital technology of the Marantz DVD player?
Thanks for your reply.