TV Flyback transformer replacement / repair

Discussion in 'Technical Repair' started by pyr0ball, Jun 16, 2012.

  1. pyr0ball

    Thread Starter New Member

    Jun 16, 2012
    3
    0
    Hiya guys! I'm new to this forum but found you guys while googling around trying to find some answers.

    Anyhoo, I do a lot of repairs to various electronics for work, but also for fun as a hobby. Anyhoo when I get a customer that's got a failed LCD or Plasma TV and I trace the problem down to a flyback transformer, I usually call it quits and buy a replacement board instead of repairing it. However for my own personal stuff I tend to go an extra mile or a hundred, and I've now got two TV's that both have failed flyback transformers.

    One I know what the input and output voltages are supposed to be and on what pins, and the other I know what the input voltage is, but only the output voltage for the whole circuit, and not the transformer's secondary winding, which is where the short appears to have occurred.

    Anyways I wanted to know if there is anywhere I can buy individual transformers if I can determine the right specs? I know wrapping a production-level high-output transformer is next to impossible without serious equipment, so I've sorta come to terms with the fact that I cant make one myself, but I'd really like to be able to pat myself on the back for fixing these boards and not having to just chuck them and replace them.

    I'm doing it this way because of the challenge, not to save money, so I'm ok with spending a bit of cash to get what I need!

    Piccy of the board I dont know the output specs on yet:
    [​IMG]

    Thanks in advance for your help! I'll post pics of the other board later as I'll need to dig it out of storage
     
  2. PackratKing

    Well-Known Member

    Jul 13, 2008
    850
    215
    Insofar as rewinding goes, what material is the coil frame made of. Molded ferromagnetic, or interlaced steel "E's" >> If the latter, you have a prayer to r/w IF you can get it opened w/o destroying it.
    If so, don't use too much tension when rewinding, and keep evenly layered as opposed to "jumble" winding if you want the finished product to work.
    New parts, are completely up to the OEM.......good luck..!!
     
  3. dataman19

    Member

    Dec 26, 2009
    136
    29
    Those are not Flyback transformers.
    ..
    Flyback transformers are used in CRT displays...
    ..
    You have a high frequency switching transformer. And the board is the Backlight Inverter Board.
    ..
    This is very much obtainable (really depending on where you are - it may or may not be a simple purchase).
    ...
    Post the Make and Model Number of the LCD/Plasma Display.
    Also include the Display Backlight Board Number.
    ...
    The transformer also has device labels (but they are not always obtainable without a device cross reference chart - They are usually ordered by what is specified in the Manufacturer's service manual parts listing).
    ...
    This looks like a Panasonic or Sony Part (but that is just a guess)..
    ..
    Incidentally, Did you test the two switching transistor mounted on the black heatsink located right above this transformer? 90% of failures in these boards are the switching transistors. The driver transistor sometimes goes as well, but the switching transistors are the most likely culpret, the transformers are more rugged, and unless they are visibly overheated and leaking lacquer/shellac - may not actually be bad.
    ...
    Also, You "must" have the backlight bulbs plugged into this board, if you power it up without a load the transistors will blow.
    ..
    The backlight bulb leads are the three pairs of leads connecting to the three pairs of white terminals on the right side of the board.
    ...
    Have you verified that the backlight bulbs are good? (If you find one that has a lot of dark discoloring on either, or both ends - it is probably bad.
    ..
    I have spare bulbs that I plug into the boards to troubleshoot. More often than not, when I plug in the test bulbs I find they all light. Then wen I remove the bulbs in the display and plug them into the board I find the one that is bad (and causing the power supply to overload and shut down).
    ...
    Just a short bit of info: When you have a bad backlight bulb, the display will tend to turn on and light up for a second or two, then shut down. This is because the Backlight driver board (the one you have pictured) will shut down if there isn't a balanced load on the backlight bulb side. This is to keep the Backlight river board from self destructing.
    ...
    Dave
    Phoenix, AZ
     
  4. pyr0ball

    Thread Starter New Member

    Jun 16, 2012
    3
    0
    First off, thanks for the clarification on the type of transformer.

    That board is not just the CCFL Driver board, but also the combined power supply for the input/processing board as well

    Already found 3-4 of these on ebay, yes, but again, I wanna learn how to repair the parts for the fun and challenge!

    Here's the testing I've done so far and why I believe that transformer is the one at fault:

    Current "normal" operation shows a gradated darkening of the screen from right to left (brightest on the side where the CCFL contacts are). They all stay on, however, just in a half-darkened state.

    While testing with my DMM, I discovered that while I was checking the AC voltage to the CCFL's, whichever CCFL I was testing would light up FULLY. I then tried grounding the contact for one CCFL, then another, and found the same effect would occur. When I tried to ground two of the CCFL's attached to the same coil, they both would fully come on, however, the TV's overload logic circuit would automatically turn the display off after a couple of seconds.

    If I shorted the contacts between two CCFL's the ENTIRE DISPLAY turned on with no darkening at all, but again the TV would shut itself off after a second or two.

    Anyways, all of that makes me think the CCFL's are all working fine, but that theyre just not getting the right voltage. And since all of them are darkening at the same rate, it makes sense that a universal source would be the cause.

    The transformer indicated in that picture is the only one that seems to supply voltages to the three other transformers use to the right of the board for the HV outputs. It has a slight burnt look to it when looked at closely, but that could simply be the epoxy darkening.

    Board information:

    RSAG7.820.1459/ROH VER.F
    Hisense HLP-30A11
    Input: AC100-240V Max3.5A 50/60Hz
    Output: 5VS/0.5A 5VM/1.5A 12V/1A
    HV Output: 1280VAC/9.5mA

    Transformer board ref: T803
     
    Last edited: Jun 17, 2012
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Have you ESR tested all the electros? ;)
     
  6. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    what you need to do is get yourself a ccl tester to check the backlights are working -there are a few ready built units available which will give an indication of what is happening before you go deeply into your invertor panel repair....i have quite a stock of different types of transformers that are used on these panels as sometimes the price of a new pcb means the customer scraps the set....
     
  7. pyr0ball

    Thread Starter New Member

    Jun 16, 2012
    3
    0
    Any chance you could point me at a tester?

    Also as i said in the first post, I've got another TV that I know the transformer is bad because I know the expected input and output voltages on each pin. The input is correct, but the output is toasted. I also know how many windings from each pin. I cant seem to find a replacement however
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    That doesn't prove anything. That transformer is one of the least likely items to fail.

    Common failure is the electro caps which will cause the symptoms you mentioned; voltages wrong, tubes lighting low brightness, lighting at one end or not at all.

    What's on the top of that large dark blue cap under the bottom heatsink in your photo?
     
  9. sheldons

    Active Member

    Oct 26, 2011
    616
    101
    the Zippy backlight tester is a good peice of kit........
     
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