Hey all. Looking for help troubleshooting vertical collapse with a CRT monitor. It's an IBM 5153 so a fair bit old. Here's what I've done so far:
- looked for cracked solder joints and broken traces
- removed the v.hold and v.size pots from PCB and tested them
- tried injecting a vertical signal directly into the sync processor
- replaced the sync processor IC (Q402)
- recapped the board
- removed the three transistors in the vertical circuit and tested them
- checked resistor R312 which, according to one forum user, caused his vertical collapse.
The most recent thing I did was check the voltages on the three transistors in the vertical circuit while the monitor was running:
Q301
b 0V
e 0V
c 48.5V
Q302
b 48.5V
e 49V
c 120V
Q303
b 48V
e 49V
c 0V
I don't know what these values can tell me or what my next steps should be. Hoping someone can help.