You didn't think I was going to get off that easy did you?
I played the speaker a few hours each day for three days with the "new" used board with no problems and high fived myself. Woke up this morning, the speaker was giving me the finger and humming. No soup for me.
I quickly opened it up and found that temps inside were around 31C-35C. The transformer that was overheating on the old board was 31C. There is a large transformer that was 38C. These temps to me don't seem very hot but there was no audio signal going in. It seems that the hum is causing the speaker to turn on from standby, or something else is causing the speaker to turn on resulting in the hum. The chicken or the egg.
The transformer that was overheating on the "old" board was a potential problem but apparently not related to the dreaded hum.
There is no method to its madness, I opened it up laying on its back I couldn't get it to hum. Stood it up, after a couple of minutes it turned on and hummed. Laid it down, it still hummed. Stood it up again, after a few minutes it stopped humming then later it started humming again. Is it possible that by repositioning the speaker, bad caps can work intermittently if they are failing?
I rolled the dice and got snake eyes, what's my next move? Should I start replacing caps, what do you guys think?