Quoted from Kawydud:I have even disconnected the connectors for the strobe and return off the cpu board and checked the transistors withe a logic probe. The transistors are not functioning like the first 4 with all wires disconnecting. It is acting like something in the cpu board is telling it to act differently.
What I have changed - all new tip 42 transistors, new pre driver transistors, new 7408 chip for the second half of the matrix, and a new 6821 PIA.
Careful with the probe and 18v. If you have a probe with CMOS setting i think that should be OK.
Anyways you have a probe and it sounds like you know how to use it. So even with the lamp fuse pulled you can check the logic stuff and find out where the signals are crapping out at. Good thing is four circuits are working OK. That means with the probe you can start at the PIA and work towards the transistor and compare working circuits to not working circuit at each step and find out where it goes wrong at.
If all four non workings circuits are connected to one 7408 chip that would be a big clue. Without looking at the schematic, 7408s are usually used as blanking protection. The blanking signal may not be making it to the one chip with all non working circuits from a cut trace or whatever.
Matthews, NC
