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Learning CRT repair.. black screen, no raster, but sound?
flgliderpilot:
Ok, I was wrong on the 3505 :( Replaced it but same symptoms.
The monitor has a high pitched whine. Flyback transformer failing?
Symptom is horizontal diagonal lines when screen control turned way up, but no picture. Brightness control has no effect.
I can feel and hear static at the screen when it powers up.
So would a failing flyback transformer exibit these symptoms?
I'm not understanding how there can be diagonal lines and screen brightness when I crank up the screen control, and still no picture if it is really a bad flyback transformer. Could someone please explain. My monitor repair book never describes a failure like this.
The whine had me convinced it was the flyback transformer so I've removed it and am searching for a (probably impossible to find) replacement.
Thanks
jordan:
Have you checked the transistors and other elements on CRT board on the tube ?
downunder:
To my way of thinking, what you are seeing on the screen is normal. With the screen pot turned up, you are overdriving the picture tube. The retrace lines you see are normally blanked out in a normal picture so they are not seen (but they are still there).
The screen is lighting up so you can discount a faulty flyback transformer. It's been a long time since I worked on CRT technology, but I seem to recall a feature known as x-ray protection, which would mute the screen in the event of too much radiation. Might be an avenue worth researching.
Might be worth checking pin 7 of the fbt as well as R330 and R476 just to the right of pin 7 in the schematic. These are part of the ABL
[auto. beam. limiting] circuit and could KO the picture. Bruce
astracat:
hi have known the 12v supply to be bad for this problem, try hot air on this transistor to see if voltage fuctuates
regards
astracat
flgliderpilot:
--- Quote from: jordan on February 10, 2018,01:46:45 ---Have you checked the transistors and other elements on CRT board on the tube ?
--- End quote ---
Yes, I've checked the transistors on the neck board, and all the transistors from the TDA3505 to the neck board. Also check the HOT.
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