Yes I've switched the RAM in both to no avail, and double checked the caps on both.

The board with garbled video had more corrosion around the capacitor terminals, but no trace damage.

The board with no sound: does appear to have a small amount of green corossion, I will check continuity.

Any chance the video ROM could be corrupt on the board with garbled video (looking at it's removable socket?)

Thanks for your input,

JB