Peter wrote:
My understanding is that it just started happening, prior to the OP jumping inside the console.
To be clear, this is what studiodaz originally said:
I have open up the board to see if any cables have come loose and also open the brain/pc end too, but I can't see anything obviously wrong.
...which suggests to me that observation was all that occurred. If studiodaz did indeed remove and re-seat (and possibly cleaned) ALL connectors, at both ends, leading to the Control Board as he says here:
Yes that was the first thing I tried, I have done this to all the accessible cables.
...then I am still of the opinion that the job wasn't done as thoroughly as it should have been. I think he missed something.
The idea that buttons other than the bank select switches are flipping banks suggests three possibilities, already suggested: re-seat the connectors, replace the RAM and reinstall the O/S.
The description of how the RAM was dealt with is suspect. The O/S seems least likely as studiodaz says he reinstalled and additionally plugged the board into a different CPU with the same screwed up bank selection results.
If it isn't the ribbon connectors then it could still be RAM....or possibly an active element on the controller board itself. The only way to rule that one out would be taking his board over to the other guy and swapping the controller board out to see if his unit works correctly with the other guys board. And as an additional verification, see if the other guys board fails with his Controller board in it.
-just sayin'...