Question about LG RU-52SZ51D 52" Rear Projection HDTV-Ready Television
My LG RU052SZ51D TV has a diagonal pyramid shaped shadow extending from the top left corner of the screen.The first ten inches are dark (but picture still visible through it, and the for the next ten inches it is a lighter shadow but extends all the way across to the top right (diagonally)
What could be the problem, and am I looking at a major repair here?
The following is when a single CRT or tube in a projection TV set starts to get weak. It is the same for a CRT when any one of its electron-guns starts to go weaker than the others.
On any CRT based set either with a single CRT or with seperate projection CRT's, as the tube(s) (CRT's) get weak their emission goes down. One of the symptoms is that the beam focus gets softer.
When a CRT goes weak the beam current will decrease. This lowers the mass or intensity of the electron beam. This makes the beam width wider, and thus the image focus is softer. Having a wider beam in a single CRT or single colour section of a CRT's electron gun also means that there will be more beam width overlap in comparison to the other CRT's or the other electron-guns in the case of a single CRT. This will give the appearance of an overlap or edging especialy with sharp or thin lines.
There is also a symptom where the convergence can get less accurate as the convergence control circuits age. This means that the scan tracking between each of the CRT's or the electron-guns in a single CRT start to not be able to accurately keep converged to each other. This will produce a border effect between the beam position accross the scanning of the screen.
Sometimes with a projection CRT set if there are separate focus controls in the high voltage (HV) section for each of the colours the beam focus may be able to be cheated if the CRT is not too weak. In most CRT sets the focus voltage is shared between all the colour channels, and thus there is no possiblity to control each channel individualy.
With weak CRT's there are other factors that come in to effect. One big one is that the colour tracking gets impossible to be accurate. This is because the gain liniarity of the tube becomes out of spec. As each of the CRT's or the electron-guns in a single tube become weak they will lose their tracking accuracy in relation to each other. In the design of the drive circuits of the better TV sets there are some auto circuits to try to make sure that the tracking is stable. But, when the electron-guns become too weak the circuits run out of range.
Posted on Dec 24, 2008
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Posted on Jan 02, 2017
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