Question about Toshiba 50H72 50" Rear Projection Television

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No picture, but power light and sound OK

I have a Toshiba 50" CRT rear projection. The picture went out all of a sudden, and when it went out the picture squeezed down to a line about 1/2" tall in the middle of the screen before it went black.
I have opened the back and found no obvious signs of burnt components (no noticeable smell, no scorchmarks visible). I opened the front and adjusted the knobs there (focus and picture). The picture knobs,when turned up, display a ribbon-like swirl across the screen in the vertical center. All three colors look that way.
When I turned the picture knobs up, I heard pops inside the set and now the red "ribbon" has a kind of broken-glass pattern of black inside of it. I am afraid I may have ruined the red CRT with my tinkering.
Anybody have any idea what the cause of the loss of picture could be? And/or how to fix either or both problems?

Thanks for your help!

Posted by on

  • Xeromem1 Nov 25, 2007

    Excellent explanation! Definitely beyond my ability. My wife called a tech out to look at it while I was at work, and the tech told her it was a bad _bulb_, one that he couldn't fix. At least he didn't charge for the visit. So I'll have to find a different shop to bring it to.
    Any idea what the broken-glass pattern in the red is from?



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  • 934 Answers

The problem you have there was a loss of vertical deflection followed by a complete failure of Q301, the vertical Ic LA7833S.
It may have been in part due to the feed caps located in that circuit and there will likely be NO outward signs of the failure.
The Ic needs to be replaced and the electrolytics in that circuit need to be measured with and ESR meter and replaced if bad.
If it's starting to sound a bit beyond your ability I strongly suggest having a qualified shop do this because you can overheat the vert Ic easily just soldering it in...
If you have a shop do it you might ask what they charge to replace the vertical Ic and ESR the caps in that circuit. Explain to them what you have here with regards to how it went out, dropping to a horizontal line before going completely dead... The more detail you can give the easier it will be for the tech to troubleshoot the problem.
Good Luck!

Posted on Nov 25, 2007

  • William Rayburn
    William Rayburn Nov 25, 2007

    You may have just turned the red drive up too high and there's really no way of telling if it did any real damage to the crt without testing...

    As for the "bulb" diagnosis - - get another tech, one more qualified. Try here may help loacte a reputable shop.




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