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Please help me repair shorted out TV power supply

Discussion in 'Troubleshooting and Repair' started by swenmasterson, Sep 29, 2013.

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  1. swenmasterson

    swenmasterson

    13
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    Sep 29, 2013
    Help me find the right metal oxide varistors please!

    Hi everyone,

    after having shorted out my lcd TV's powersupply which I was in the process of repairing, I've been trying to troubleshoot what components need to be replaced.

    I have already replaced the fuse, now I am at the stage of trying to find new MOVs however, I cannot seem to locate the right part by googling the writing on them. I've also tried searching for the schematic of the board but with no luck.

    The powersupply comes from a European LG32LX2R TV. There are 4 small MOVs and one slightly larger one on the PCB. Please have a look at the photos and help me find the correct replacement MOVs or something close that I could use. Thank you very much and please ask for more details that could help you identify the parts! :)

    http://i.imgur.com/7NbAwE3.jpg

    http://i.imgur.com/TMdpESf.jpg
     
  2. shrtrnd

    shrtrnd

    3,767
    487
    Jan 15, 2010
    Look, there's no reason for four MOV's in your power supply.
    Those are capacitors.
     
  3. swenmasterson

    swenmasterson

    13
    0
    Sep 29, 2013
    Ahh, you are probably right. I was wondering why they would label them as "CY" on the PCB:D I read this article http://www.techrepublic.com/article/put-your-power-supply-to-the-test-with-a-multimeter/ which led me to believe the MOVs would be the next components to change (and confused them them).

    As they are capacitors, I can replace them with a higher rating capacitor just to be safe, since I do not know what specs they are, right? Any recommendations?

    Also, would you have any recommendations on what to change on a shorted out power supply? I left the PCB on a metal surface and plugged it in to test the TV and the fuse blew. Since then it shows now signs of life, no relay click, led etc... Thanks
     
  4. shrtrnd

    shrtrnd

    3,767
    487
    Jan 15, 2010
    You're describing about the worst possible scenario I can imagine for a circuit failure.
    If you energized the circuit with the board on a metal surface, ANYTHING (and probably
    a lot of things), can be damaged now.
    I don't know what you mean by a 'higher rating cap', the ones in your picture are 1000pfd caps, probably rated about 1000V.
    Your fuse blew, but not in time to save other components. You might have ONE varister
    in there that will also be blown.
    Nobody here is going to be able to help much without a schematic or at least a picture.
    I know you're in trouble, and people here like to help, but we need as much info
    about your issue as possible (Make and model of the equipment for starters).
    I have little doubt that you've lost semiconductors in this mishap. I've seen cap issues
    with pin-hole internal failures, but the odds are the caps you pulled were probably ok.
    You've probably got semiconductors that took the hit.
    Do you have a digitial multimeter if you supply additional information? Because you'll
    get advice about what to check from people on this site. A schematic of the power
    supply is a lot of help, and a picture of the board will help because a lot of guys on this
    website are magicians with pictures of circuit boards.
    It doesn't sound like you've got a lot of experience with components.
    Your best bet is to buy a replacement power supply board.
    If you want to try to troubleshoot the problem, and have patience, people here will
    help you with the issue if you want to go for it.
     
  5. swenmasterson

    swenmasterson

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    0
    Sep 29, 2013
    shrtrnd: Thanks alot for your reply. I do have a digital multimeter. Ill post pictures and information as you suggested in the electronics repair section. I am pretty much a beginner at this and would like to make this my hobby, thats why I bought the TV in the first place - just to basically learn more about electronics and circuits :) Id like to make the TV work by fixing it myself :) I have replaced caps in an lcd monitor and messed around with a breadboard and really found interest in electronics.
     
  6. shrtrnd

    shrtrnd

    3,767
    487
    Jan 15, 2010
    What you want to do is what people on this site like to see. Somebody who wants to
    do things themselves, and are willing to work at it.
    The DMM is needed to make simple electical checks, you need one of those for almost
    any repair.
    You'll get plenty of people trying to help you with this, when you can show us in
    pictures what's going on. We'll be asking you to make some electrical checks when
    we see something that should be checked. If you don't know how to check some of
    the components, people here can tell you how to make the checks and measurements.
    You may not be able to make a successful repair this time, depending on the problems,
    but I think you've got the best shot at a successful try, by coming here.
     
  7. swenmasterson

    swenmasterson

    13
    0
    Sep 29, 2013
    Thanks for the encouragement shrtrnd! I am really glad I found this forum. Even if the board is beyond repair, I could learn a lot in the process, so I am ok with that. Ill post pictures and the description of the problem in the repair section as soon as I can :)
     
  8. swenmasterson

    swenmasterson

    13
    0
    Sep 29, 2013
    Hi everyone,

    Please help me reapair my LCD TV powersupply. First off, Id like to say that I am a beginner at electronics, so far Ive soldered a few things, programmed an atmel chip and replaced bad capacitors on a TV. Because I like to learn, I bought a faulty LCD TV to try and fix it.

    Everything indicated that the caps were shot, however the TV turned out to be in full working order. It had one minor issue - some colors showed a dark shadow on the screen. I thought this was a warped difuser and proceeded to try and fix this problem.

    When I tried to test my repair I left all the boards outside to make it easier to access them if need be. This is where I made a huge mistake. When I powered on the TV I left the PSU board on a metal surface and shorted out the pins underneath the board. My circuit breakers went and the TV showed no signs of life after this.

    I really dont need the TV and I bought it just to try and learn more about electronics, thats why I dont just want to replace the whole PSU.

    The TV is a European LG32LX2R.

    This is what I have done so far:


    1) replaced the fuse on the PSU

    2) desoldered 5 ceramic caps (I mistook them for MOVs, which I read should be replaced after the fuse) These are missing on the board, however I will solder new ones on.

    User shrtrnd kindly suggested that they are most probably 1000pF rated at around 1000V ceramic caps. But Id like to be 100 percent sure I am using the correct part. The caps that I removed and thus need replacing are 4 smaller ceramic caps labeled CY101, CY102, CY104, CY105. CY103 is slightly larger and spans across the "primary" part to the "secondary" part of the PSU.

    I have located the parts list, however I cannot seem to find "CY" caps on there. Could you help me with this also?

    I you could teach me how to test parts one by one using a multimeter I woud be very greatful. Please go easy on me with abbreviations and industry slang, I am a beginner at this :)

    Photos of the board:
    http://i.imgur.com/RoVb4fq.jpg
    http://i.imgur.com/F1tTnak.jpg
    http://i.imgur.com/hgAdE0m.jpg
    http://i.imgur.com/2lotbYC.jpg
    http://i.imgur.com/dWvie1w.jpg
    http://i.imgur.com/EftmDhA.jpg

    Parts list:
    http://www.brelect.fr/ve/32LX2R.pdf

    Thanks in advance guys and sorry for the long post! :)
     
  9. swenmasterson

    swenmasterson

    13
    0
    Sep 29, 2013
    Anyone? :)
     
  10. shrtrnd

    shrtrnd

    3,767
    487
    Jan 15, 2010
    Don't dispair. The people on this site just check-in once in a while, and while people
    like me in the States are awake, a lot of the the other guys in Europe and Australia are sleeping.
    I'm at work right now and people will be checking this site over the next day or two.
    We haven't forgotten about you, we just need time look at what you've got, and to reply. We don't have one person available 24 hours a day to make immediate responses. Hang in there.
     
  11. shrtrnd

    shrtrnd

    3,767
    487
    Jan 15, 2010
    Getting a msg saying 'imgur is overloaded'.
    Will try to access your photos later.
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,412
    2,780
    Jan 21, 2010
    One of the problems is that you've used a flash. This results in a type of lighting which makes it very hard to see the sort of details we need.

    It is best to take the board to a place that has bright indirect lighting (under an overcast sky or in shade).

    It's probably best to take some closeups of chips so we can see if any of these show obvious damage. I can't see any burn marks, so can't suggest what the best place might be to start.

    Note that the chips on the heatsinks are also worth looking at.

    Are you saying that when you apply power not, nothing happens at all, and that the fuse is intact?
     
  13. shrtrnd

    shrtrnd

    3,767
    487
    Jan 15, 2010
    What *steve* said, and also:
    Troubleshooting is like cooking, everybody's got their own way to do it.
    (And you'll probably get plenty of different suggestions here)
    The first thing I would do, while you're trying to get closer pictures with less glare), is to the check the power semiconductors bolted to the heatsinks. (The black square devices
    bolted onto the silver, finned, heatsinks).
    A simple, easy, first check is to use the ohmeter to check the resistance values of
    the components with the exact same part number written on them. Sometimes it
    depends on how the rest of the circuit is wired that's connected to them, but if you
    check the values between each of the pins on each component, they often are pretty
    similar to one another. What you're looking for, is a radical difference in the values you
    read on one component, to all the other components with the exact same part number
    written on it.)
    The reason I'm suggesting this first is, that some of those semiconductors can be
    expensive, and there's no guarantee that just replacing those items will fix the problem. So if you have a lot of obvious damage there, you know not to spend a lot
    of money willy-nilly, buying replacement parts that could end-up costing you more
    than the cost of an entire new board.
    What you're looking for (you're using the ohmeter function, the board MUST be unplugged
    and without any power), is a shorted or open semiconductor.
    A shorted component will read very, very low resistance, and an open one will display
    'OL' (overload), or a very,very high resistance becauise of all of the other components
    connect to the one you're testing in-place).
    With what little we can see so far, that's where I would start, just to see how bad the
    damage is. Any questions about how to use your meter, just ask.
     
  14. Nobody

    Nobody

    12
    1
    Aug 31, 2013
    Two things jumped at me:
    1. White residue on low voltage section and to lesser degree everywhere else. Might be water damage. Don't have to be spill - might be condensation.
    2. Lots of discoloration - it runs hot!

    I think most of the caps you took out are from power filter and TV probably will run just fine without them.

    It appeared that C133 runs hot (discoloration of the board right under it). It should not.
    If it boils out - Q101 and D102 might go. Check them for shorts and proper junction forward voltages (if transistor is bipolar, not FET).



    If there is any hope for this board, first wash it with proper board wash/cleaner, both sides. Google for the guides to properly wash PCBs. Make sure there is no hint of white residue, especially around small parts like IC301.
    Then change C133 and if necessary Q101 and D102.
    Put caps you took out back. They very rarely go bad, almost never.Just check them with meter, they should check open.
    Change ALL electrolytics next to largest heat sink, all low voltage section. To the bunch you may also change electrolytics in hot (high voltage) section as well.
    After all done check EACH low voltage output for shorts. Often there is zenner in parallel with output to prevent further damage to the main board when power supply for some reason goes over-voltage. I don't see any on the pictures but I might miss it.

    If you buy caps in bulk from China it will run you about $20 total. Not sure about Q and D.

    If white residue turns out to be water damage - see if other boards may have the same. If there is a lot of it on other boards - I would not bother. If it is condensation - you probably will see more next to the vents/grilles or where air draft would be. The sign that white stuff is from water - you can wipe it with your finger from solder mask (green area), but it is very persistent on solder joins. Usually even after board wash it is visible on the joints though to the lesser degree.

    Never run these boards without load! They usually require minimum load. Without load they may over-voltage and pop.

    Good luck!
     
  15. swenmasterson

    swenmasterson

    13
    0
    Sep 29, 2013
    Thanks for all the helpful tips and observations! My apologies for being impatient. Unfortunately, I had to scrap this project since I live in a really small room and the TV was taking up too much of my living space, the lack of time (have to work on my thesis and school work) doesnt help either. I bough another LCD TV with a faulty powersupply. This TV is only a 19inch, so its manageable for me to keep it and work on it over time. Ill make a new post describing whats wrong with it. Ive also made pictures without flash glares so if youd like to help me try and fix it I would really appreciate it. Thanks again guys.

    I would also like to kindly ask the moderator to close this thread. Thank you.
     
    Last edited: Oct 28, 2013
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