I can't tell you which one it is, but it may also be due to a bad crimp somewhere in your display cable as was the case in a recent repair. In that case it was all or nothing not a garbled screen. But a garbled screen might be from pins 1,3,5,7, or 9 because these are the signal pins from the CPU. It's unlikely a power issue because these are redundant.

The numbering convention I am using is with pin 2 all the way on the right side of the display header in the row closest to you when facing the Empeg screen towards you and pin 20 all the way on the left.

Hope this helps,
Stu