My screen went blank. It was a graceful failure over time which I thought was heat related. Finally, the cursor disappeared and there is no light at the CRT yoke. I dug through the manuals and found the following trouble shooting steps:
1. Brightness control (R1) turned down.
2. Anode voltage incorrect.
3. Grid voltages incorrect (G1, G2, G4).
4. No cathode drive.
5. Transistors Q901, Q902.
6. No video signal coming from terminal logic board.
7. IC U406.
8. Video circuits on logic board.
9. Diode D901.
10. No sync pulses coming from logic board.
11. Diode D209.
It's not number 1 :-). I've adjusted the Brightness control several times. Guess I'll start looking at the other steps. I thought it was heat related, so I placed a 5" fan on the side of the case a month or so ago. I turned it off while running errands just now and it was still dead after an hour.
Wait, You guys are awesome!! Simply typing this help message caused it to come back to life. I only have a cursor since I'm using Les's H19 emulator to run the H-89 currently. At some point I'll put the system back together and a working screen will be important.
Any ideas on what is causing this random failure?