bad flyback.
For potential power supply issues, you can monitor the B+ line feeding the Horizontal Output Transistor with a multimeter, as time goes on you can monitor this.
But ive seen this in the past with other monitors, and its always been a failed flyback, because the Focus/G2 block starts to go bad on the flyback itself. Eventually it shorts and will blow the neck on the CRT (intense arc/cracks neck).
the HV has a built in regulator/x-ray protect circuit. if the HV starts drifting out of spec, the focus/brightness will as well. But the X-ray circuit will trip shutting down the monitor. Bad caps in the HV regulation circuit could cause this, but as i said it would effect overall brightness. You could grab a high voltage probe and stick it up under the anode cap. Watch the reading as the focus drifts. if it stays solid, replace the flyback. If you cannot find a replacement/NOS flyback, you could go the hacker route and disconnect the focus lead off the CRT along with the G2/Screen Drive lead.
Trim those back and HV corona dope/isolate them away. Use an in-line focus/G2 block off the high voltage anode lead (like how projection TVs did it). And problem solved.
For potential power supply issues, you can monitor the B+ line feeding the Horizontal Output Transistor with a multimeter, as time goes on you can monitor this.
But ive seen this in the past with other monitors, and its always been a failed flyback, because the Focus/G2 block starts to go bad on the flyback itself. Eventually it shorts and will blow the neck on the CRT (intense arc/cracks neck).
the HV has a built in regulator/x-ray protect circuit. if the HV starts drifting out of spec, the focus/brightness will as well. But the X-ray circuit will trip shutting down the monitor. Bad caps in the HV regulation circuit could cause this, but as i said it would effect overall brightness. You could grab a high voltage probe and stick it up under the anode cap. Watch the reading as the focus drifts. if it stays solid, replace the flyback. If you cannot find a replacement/NOS flyback, you could go the hacker route and disconnect the focus lead off the CRT along with the G2/Screen Drive lead.
Trim those back and HV corona dope/isolate them away. Use an in-line focus/G2 block off the high voltage anode lead (like how projection TVs did it). And problem solved.