Sharp concentrated beam across the middle of the screen

Old 01-18-04, 01:51 PM
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Angry Sharp concentrated beam across the middle of the screen

Decided to clean the dust out of the Mitsubishi TV. Opened the back and blew out all the dust. I put the TV face down while I was doing this. I used a small brush to help get the dust out.

Put the back on again and powered it up. The sound is fine but there is a bright horixontal beam of light in the middle of the screen that flickers. Its about 1cm thin. The rest of the screen is black.

Stupid me I should have left it alone.
Any help or advice would be greatly appreciated.

Old 01-20-04, 02:10 AM
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Sounds like a compenent in the field scan circuit (vertical scan) has failed. I guess it was about to break anyway - you probably helped kill it by opening up. Even if you did not, it probably would not have been too long before it broke.
Old 02-01-04, 04:52 PM
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Once apon a time I worked on a few tvs in school and in those days what you discribe was a real common problem exspecially in house holds with small kids. the reason was that on the back of the set was a "service" switch that shut off the vertical output to allow adjustment to be made. I dont think that they still place that switch on the outside any more 'cause I haven't seem one in a while but there may be one inside. Is it possible that you may have moved it? hope this helps havent worked inside a TV scince they took out the tubes.
Old 02-02-04, 02:58 AM
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Being an 'Oldun' I remember that switch . It was operated when the 'greyscale' needed adjusting. I'm fairly sure they won't be found in more modern TVs.

There could be a faulty component if the TV is fairly old but equally likely is a bad solder or plug and socket connection that has been disturbed by the brush, or the movement of the chassis.

Follow the leads from the scan coils (around the neck of the tube) back down to the main panel. Not the ones that plug in near a big transformer with a thick lead coming out of it. There will be a some that plug in elsewhere. Have a good look in the area where these go, with a magnifying glass maybe. Look out for an upright I.C (chip) bolted or clipped to a metal heatsink nearby. Look at the solder connections of that particularly.

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