Hello,
I am trying to bring a sys80b alphanumeric display board back to life. Tested R1 and it was toast, and after replacing it, the display works (so the glass is fine), although the new R1 is blistering hot within seconds, and I'm sure won't last. What would cause R1 to get too hot?
I replaced the big 470uf cap, and also replaced R2 (R2 checked out fine though).
I checked the two zener diodes VR1 and VR2, and they are not totally open or closed both ways.
On my working display board, checking the voltage across VR2 and C2 when on, I get ~14v, and ~17v on the one that's burning R1 (also get ~17 on the bad board across cap C2).
I've checked R4, R3, and R5, and they check out.
I have not checked CR1-CR4 yet, nor R6-R15. I though someone might have an idea what to look at before I start lifting everything up.
Would the Q1 transistor have anything to do with R1 getting too hot?