I have an Atari display that is missing some segments. It's the version 2 board. The problems are on the 'c' & 'e' segments on row 1, 'a' segment on row 3, all segments on the last column, and player 4 "Up" light.
What I've tested so far:
Swapped the display glass with another machine, so I know that part is good.
Swapped the entire display assembly and that works fine, so it seems it's not a problem with the MPU, aux board, ribbon cable, or connectors.
Tested continuity from the display pins on the back of the board to the contacts that touch the display glass.
Cleaned the contacts.
For that 'a' segment, I tested Q15 (in circuit), which comes from J21 pin 23. That pin also goes through RP2 pin 9, R15, and R54, then to pin 13 of the 4511 decoder chip. I know that bad resistors and transistor are a common cause of missing display segments. Before I trouble with pulling those out, I want to probe the pins on the decoder chip. The schematic shows that the chip takes in 90v. The data sheet on the CD4511BCN says it only handles up to 18v, so I'm confused by that.
With such a high voltage, I don't want to meddle with powers that I don't understand. I'm looking for advice about how (or if) I can test the chip in the board. I figure I can pull it out and test it on a bread board but then I might as well replace it with a new chip.