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CRT TV screen problem.

Discussion in 'Troubleshooting and Repair' started by Achui, Jul 24, 2020.

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  1. Achui

    Achui

    2
    0
    Jul 24, 2020
    I was tinkering with an old crt tv I found at the used store.
    It was working for a few hours after I brought it, then it shut down after sounds of sparking.
    There was arching due to leakage from the LOPT.
    I replaced the flyback transformer and the TV is back on but the screen has a lot of green and slanting lines.
    Any solution/suggestion would be a great help!
    The TV is a 29" philips, the model is - 29pt5607/94. Im not sure which year it was manufactured though. Screenshot_20200724_165055.jpg
     
  2. shrtrnd

    shrtrnd

    3,816
    518
    Jan 15, 2010
    I can tell you what I'd try, with the opinion that you might not get this fixed.
    You said it was working, then you heard sparking and it shut-down.
    First I'd look at every component inside the chassis to try to determine what was sparking, because that usually gives you burn
    marks to tell you what component was causing the problem. (Make sure it's unplugged before doing anything in there)
    You probably know, but in case you don't, a CRT acts as a capacitor, storing several thousand volts at the anode plug (connected to the flyback) even when the TV is completely disconnected from the power source. Don't hurt yourself getting zapped.
    Somehow, you determined that the flyback was the problem and replaced it. Did you also replace the large diode found across the flyback transformer, and anything else connected to that flyback that might have been fried.
    The lines would indicate to me a problem in the vertical circuit, usually a power transistor, but the green screen makes me wonder
    just how much circuit damage you've got there. (unless your color or tint was off in the first place)
    Again, I'd go over the components closely, trying to find-out what was sparking and identify what circuit section you should be concentrating your troubleshooting efforts on. Sparking you can hear would imply high voltage, the usual suspects for that are
    the power components. Large capacitors and power semiconductors.
    I'd find the sparking source and then trace the components connected to that source to find-out what else was damaged when the sparking occurred.
    My experience with the CRT TVs, because of their age, is that Large Electrolytic Capacitors dry-out and fail, that causes stress on the power semiconductors, causing them to fail, and if any of those failing components don't open (acting as an unintentional fuse, to interrupt the uncontrolled voltages coursing through those components), you have a cascading effect that takes-out more than one component or two.
    Sorry if I'm no help to you. For me anyway, it's a lot easier to actually look at a circuit, than to theorize with words.
    Good luck.
     
    Achui likes this.
  3. Achui

    Achui

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    Jul 24, 2020
    Hey Shrtrnd, thanks a lot! I admit I was rushing it a bit coming to the conclusion that the problem was with just the flyback and replaced it right away.
    I'll check the power components and try to trace what else got fried. I'm almost sure I didn't see any burnt marks, but I'll check more carefully again.
    Thanks again, I'll be back with the results.
     
  4. bertus

    bertus Moderator

    1,760
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    Nov 8, 2019
    Achui likes this.
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