Rockola 1475 Hum Issue

Greetings jukebox afficionados. My Rockola 1475 is giving me headaches. I recently had the amp and receiver rebuilt by a reputable technician. On the bench it sounds fantastic. However, when installed back in the jukebox, I get a noticeable hum (60 Hz?). The tech has come to the house to try and isolate without success. He has sequentially removed inputs while testing to the point only the volume control and amplifier are connected to the receiver. Still the same hum. Back on the bench it tests perfect. He was thinking on his next visit to bring an isolation transformer for testing. He has run out of ideas. Might anyone reading this be able to offer some suggestions? Thank you!

Hello jukester2,
follow this procedure: [forum.jukebox-world.de]
Rgds Jürgen

Thank you. I will have my technician look into it.