Thanks Wotto,
No problem at all helping you out with this issue. It was a shorted TIP107 transistor (Q91) which someone had replaced before (badly) with a BD902. The fix took all of about 10 minutes, after we got hold of some suitable transistors.
I keep alot of spare IC's and transistors etc., but I didn't have ANY TIP107's around. 
After a bit of Googling, downloading datasheets for various transistors, and consulting the Jaycar catalogue, we found an equivalent to the TIP107 that Jaycar Wollongong had in stock (BD650 or BDX54C). A quick trip to Wollongong and back for Wotto and the repair was done.
All the IC's and transistors were tested in both the lamp columns and the rows and no other problems were found. 
Glad to hear that this has finally fixed the problem. The next job will be to fix up that set of missing header pins and hacked wiring on the bottom of the board.
Anthony
Ahhh, it all makes sense now!
You just can't use any old part... you MUST use the correct part, or an equivalent with matching specs!
