HK 3490 receiver with no sound?

It's the classic case: I sold my 3490 that I had been using and it had been working fine. The buyer set it up and all functions worked but there was no sound. It has pre out and main in, and I don't use the factory jumpers but instead a better quality IC. So when I packed it, I inserted the jumpers. Buyer sent back the amp. I set it up, all functions worked, but no sound. I checked factory jumpers, they were inserted incorrectly; I corrected the placement; and the amp worked fine. After the fact, the buyer said he tried every possible way to insert the jumpers. He lives in a 100yr old house and plugged the receiver into a power strip along with a subwoofer and TV.
Any reasons other than the jumper screw up for the malfunction? He wants to try the amp again.
I would say it was either the jumpers were misplaced, or he had the speaker selector switches turned off. There's no reason any of the other stuff (ie power strip, sub, etc) would make a difference.
OK. Thanks. That's basicly the opinion I gave him. But wanted confirmation.
I believe that the jumpers had to be connected to pre-out and amp out horizontally. Also if headphones are connected, it will automatically cut off sound from the speakers.
You are right. I have them inserted horizontally which is left-to-left and right-to-right channels. I've put it through its paces a couple of times and powered it on and off and my instincts tell me that the amp is not faulty. He wants it back. So hopefully all will end well.
I had this receiver for 5 years with Bose 901 speaker setup. Bought a replacement that was identical. After hookup there is NO sound from any speakers, Bose 901 or Speaker 2, regular, also no sound from headphones. Went through factory reset. Did switch Spkr 1, Spkr 1+2, Spkr 2 - same result. BUT I do have a wireless AR speaker that when plugged into Tape-out jack plays just fine. I tried completely disconnecting the Bose 901 amplifier unit - no difference. Tape Mon switch on or off doesn't make a difference. Mute is not on.
I had Bose 901 amp plugged into pre-out and amp-out and after disconnecting to see if that was the problem I did not put jumpers back. Could that make the difference? If so, can someone tell me where the Bose 901 speaker amp should be plugged into the HK? I forget where I used to have it in the previous unit (should have taken a photo of back before disconnecting everything).