Somebody must tripped on my speaker wires. I turned on my Harman and
Kardon AVR100 and after 3 seconds, it went to protect mode (red button
ring). I found out that the speaker wires were pulled from the
speakers and were shorted. I disconnected everything at the back of
the receiver and turned it on but just the same, it goes to protect
mode after 3 seconds. I checked the fuses visually and they seem to be
ok.

What could have been damaged? Is it worth fixing?