I turned off my 6 mo old 20mt4405 a couple days ago and later when I went to turn it back on I got an almost entirely black screen with about 1/2 in line of color/video in the middle of the screen and it's making the most horrible high pitched squeal. Anyone know what caused this and how I can fix it?
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Re: black screen, high pitched squeal
A set that has only a 1/2 inch bright line through the middle of the picture, from left to right, has a vertical output IC that is not working correctly. If the 1/2 inch line is in the middle but going up and down, then the horizontal yoke circuit has stopped working. These are problems which should be looked at by a qualified tech, but if the set was purchased 6 months ago then it should still be under the manufacturer's warranty.
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Aug 23, 2013 - Uploaded by ShopJimmy.com
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Get it to a tv dealer but my guess is its died. It may not be economical to repair but you may be pleasantly surprised and its a small job. LG are usually pretty good so I'm surprised its gone at this age.
A high pitch sound can be a capacitor losing power it would sound a bit like a fire work. most have back up on the board but it put more pressure on them the more times you use the tv. would check them and replace. all of them can be 5 in a row in some models.
This is only a guess on my part, but if the potentiometer you replaced is part of the feedback loop and either of the outside legs are open, the circuit will be infinite gain and have a parasitic oscillation you describe; many gain circuits in pro gear are configured this way. Also, since you did replace the pot, it would be easy for you to check this first to make sure these connections are secure as it may not be a co-incidence, but still related to the original fix. Hope that helps.
The high pitch popping that you are hearing is arcing in the high voltage circuit. I would not suggest a repair on a set that is this old. Convergence repair plus a high voltage problem could run around $500-$600. But it is your call on the repair, I can only advise.
I hope this helps you.
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