Creech,
I've always been keen for one, as i thought they would be a good project - but never knew too much about them - i saw this advertised at a garage sale and went straight over. We had to come back 1.5hrs later with the trailer and the lady said about 15 or 20 people ad wanted it since. She and her husband were far from handy at fixing things and said they never used it...so good luck to me!!
That is a great story, and something to remember in the future, as this machine won't be last you will pick up ! Well - Not for $40..
Just looking at the problem, and while waiting for Gavin's advise - have you reseated the connectors going to the Master Display unit ? That's the big display.
Also, the 40 pin interconnect is notorious for causing all sorts of weird problems on Williams machines - while you are waiting, you can gently remove the driver board from the head and then refit... It the problem changes, them that's the first thing I'd work on..Replacing the connectors..