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Apple 12" RGB (LC Monitor) - Focus Issue
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Apple 12" RGB (LC Monitor) - Focus Issue
I've got a 12" RGB, commonly known as an LC Monitor (the kind a shadow mask tube in place of a Trinitron), and am having some focus issues with it which seem to go beyond the internal focus knob (which I have not yet tried adjusting).
When I turn the monitor on, the focus is fine. As I leave it on, it goes out of focus. This became worse over time.
I get a feeling this has something to do with a component in the power supply. It seems to be fairly common on this model of monitor. If anyone has a guess as to what this could be and what I would need to fix it, please let me know.
When I turn the monitor on, the focus is fine. As I leave it on, it goes out of focus. This became worse over time.
I get a feeling this has something to do with a component in the power supply. It seems to be fairly common on this model of monitor. If anyone has a guess as to what this could be and what I would need to fix it, please let me know.
I, too, have this issue with my LC Monitor, and would like to know if it can be repaired.
I'm not very knowledgeable when it comes to CRTs but I am thinking a bad capacitor myself on the power board.
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.
This site explains exactly as I am talking about. Funny that i actually found something like this. lol.
http://www.jestineyong.com/?p=562
And this is where you purchase the new Focus/G2 block:
http://www.noahtec.com/mbb.htm
And here is the site to perform that hack i was talking about:
http://www.electronicrepairguide.com/flyback-divider.html
In case you are wondering, Ive done this before several times. But of course back when i fooled around with CRT monitors, this stuff wasnt documented on the internet. Now it is, so its easier to look at/learn/do.
http://www.jestineyong.com/?p=562
And this is where you purchase the new Focus/G2 block:
http://www.noahtec.com/mbb.htm
And here is the site to perform that hack i was talking about:
http://www.electronicrepairguide.com/flyback-divider.html
In case you are wondering, Ive done this before several times. But of course back when i fooled around with CRT monitors, this stuff wasnt documented on the internet. Now it is, so its easier to look at/learn/do.