System 11 top display line not working

new display, prob original. putting one in a whirlwind as we speak.

Top line of all displays? Check the output pin 10 with a logic probe to that top segment control from u41 PIA, which then goes through a resistor/capacitor network, then onto the display data (looks like pin 19 on my bad scan of the schematics).

If you have any corrosion around that area it needs to be cleaned up as well.

Issue is on the display board as it follows the display to other machines.

My guess is bad udn chips. Common failure point and unless you have parts displays laying around you can't buy them to fix it. If i were you, I would buy rottendog/xpin/pinscore led displays and then sell this to recoup a little bit of it. Someone can pull the glass to a board with outgassed displays or potentially fix it if they want to track down what chips are bad.

I interpreted his original message as the cpu board had the same issue regardless of machine.

No, you are right. I misread when he said he swapped the cpu board. Somehow missed it is mostly working.

Ouch, that is some crusty work!