I have worked in Audio stores for almost 50 years and only encountered a similar situation once. Guy had bought a Fisher HiFi VHS machine and brought it back saying it didn’t work. We hooked it up and it was fine. 2nd unit, same result. I went to his apartment in Boston’s South End to see what was going on, and sure enough the thing had no output at all, plugged into the same amp input as his CD player, which played fine. Cables were checked. Finally occurred to me we were located a block from the Prudential Tower, where a lot of broadcast antennae are located. I switched him up to an NEC deck, and all was well! RFI was the culprit, and the NEC had effective shielding, where the Fisher didn’t. This was after Fisher was bought by Sanyo,