@swampwalker,
By chance did you unplug all the other associated audio equipment from the wall AC power outlet? Audio equipment near the amp as well as the speakers?
By the way the reason you hear a loud buzz from the amp/speakers with the shorting plugs removed from the inputs is due to RFI/EMI that is allowed to enter the open input ports/jacks of the amp.
By chance do you have another pair of speaker cables you can try? If you still have the hum using different speaker cables that would rule out the cables, ime.
Edit:
Also are you using an aftermarket power cord on the amp? If so did you take the power cord with you when you took the amp to the repair shop to have it looked at?
Just for the heck of it install the factory power cord that came with the amp. Check for the hum.
Jim
By chance did you unplug all the other associated audio equipment from the wall AC power outlet? Audio equipment near the amp as well as the speakers?
By the way the reason you hear a loud buzz from the amp/speakers with the shorting plugs removed from the inputs is due to RFI/EMI that is allowed to enter the open input ports/jacks of the amp.
By chance do you have another pair of speaker cables you can try? If you still have the hum using different speaker cables that would rule out the cables, ime.
Edit:
Also are you using an aftermarket power cord on the amp? If so did you take the power cord with you when you took the amp to the repair shop to have it looked at?
Just for the heck of it install the factory power cord that came with the amp. Check for the hum.
Jim