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Photos of an open amplifier at https://photos.app.goo.gl/k38BX1ynQdjGdYZA6
Relays were clicking at random and odd times. An intermittent fault. Seems to have been loose connections, either in the solder joints near the relays or the rotary switch at the front, or a bit of both. After redoing/re-touching solder joints around the hot resistors and bypassing the selector switch with a solid, soldered short circuit, the fault seems to have went away. But intermittent faults are hard to judge in a short time span.
The PCB with the speaker relays and speaker terminals (binding posts) can only be removed if the mains transformer is removed or the whole back plate is removed first.
I found darkening of the board around the resistors for dropping the voltage (limiting the current) to the relay coils from 50 to 24 V, R639,R640, R641,R642 all of 640 Ohm 1 W, placed very close to each other. Looks like they get hot for the engaged larger relays, but not the series resistors for the coil for the headphone relay, which are higher resistance 1500 + 1800 Ohm, and thus lower heat loss.
The coil currents runs through the rotary output selector switch which connects none/either/both lines to GND.
Fount on the net:
Bad speaker relay exchanged: https://www.youtube.com/watch?v=_tNIySrzYpU
Report of failed output and a photo: https://www.reddit.com/r/audiorepair/comments/3zryai/denon_pma560_left_achannel_not_working/
General data: https://www.hifi-wiki.de/index.php/Denon_PMA-560
Relay type for speakers could be: DEC type DH2TU 24 V DC (contacts rated 3A 120 V DC)
3. relay (smaller) for headphones could have the designator “RY-12W”.
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