Connect with us

I need help with a transformer replacement on power supply board

Discussion in 'Troubleshooting and Repair' started by NickatNite, Aug 13, 2012.

  1. NickatNite

    NickatNite

    2
    0
    Aug 13, 2012
    I need help figuring out what transformer I need to fix the power supply board for a tv I am trying to repair. I have figured out which transformer it is but I can't find the same size transformer. It has four inputs and eight outputs. The base is 4cm by 4.5cm by 2cm. I am pretty sure that is it is a step down to 5V from 120/240V but I am not sure.It has the markings MH-8573 0810. I tried to google it but I couldn't find anything about it. I really need to find it because it will save me $100. The sticker on the board says the outputs are as follows:
    24V---9A
    12V---3A
    5V ----4A
    5V --- 1A SB ( what does the SB stand for).
    If it helps the board model is TOM277CABB and it was made by Starmen it also has a part number (P/N R4041203026)

    One more thing, the ratings for the outputs are 24,12,5,&5 but when I was testing to try to figure out the problem I didn't read 24 or 12 anywhere. When powered up one of the transformers puts off over 300V DC and the rest of the board puts off about 60V AC, and in one spot it is 5V DC on one resistor and the whole left side of the board didn't have any power. (the side that the transformer I removed powered.)

    Anyway any help would be great! Thanks
     
  2. shrtrnd

    shrtrnd

    3,665
    453
    Jan 15, 2010
    First, what makes you think the transformer is bad, just because you're not seeing
    the voltages you expect, or burn damage to the transformer?
    When you're reading voltages from a transformer, you need to be using the correct
    ground or your voltages will read wild numbers.
    Also, the transfiormer voltages can read differently depending on the load, or lack of
    load.
    Before you go swapping the transformer, maybe you could supply a llittle more
    information about your problem.
    It's possible the 5V-1A SB, means the 5V output uses a 1Amp, Slow-Blo fuse.
     
  3. CocaCola

    CocaCola

    3,635
    4
    Apr 7, 2012
    My guess is that it's the Stand By power system, that will kill all the other supplies and wait for input to turn on...

    And I have to agree with shrtrnd in that unless you are positive the transformer (and only the transformer) is bad you might just be taking a stab in the dark and not getting anywhere...
     
  4. whiskeycat

    whiskeycat

    8
    0
    Apr 11, 2012
    transformer

    I think these seldom go bad...I used to work in a repair shop. You didn't say what make and model this tv is. Try calling Andrews electronics...you can find them on the net. They have always been very helpful to me.
     
  5. NickatNite

    NickatNite

    2
    0
    Aug 13, 2012
    Sorry I thought my response to your response was posted two days ago, don't know what happen. Anyway I understand that it is kinda taken a shot in the dark but I have already removed it from the board and I am going to find a replacement and hope that I was right. I just wanted to know how to low for a transformer that has 4 in and 8 out. I haven't been able to find any like that, most of the ones I see on Mouser or digi key are 4-4 what would I type into find it.

    As far as my original problem goes, the tv doesn't turn on, the power light goes from red (standby) to green (only after I changed the caps, before that it remained red no matter what) and you can even hear a click that you would expect to hear from any working tv when you turn it on. The board has power in every part except the part that the transformer I removed was suppose to be powering so that is why I am trying to give it a shot.
    Thanks have a great day
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,174
    2,690
    Jan 21, 2010
    You are unlikely to find a stock replacement. (edit: at places like Digikey)

    In any case, you would need to know a whole lot more about the transformer.

    Since you have it out of the circuit now, make some measurements.

    It sounds like there are 2 windings on the input side. Measure their resistance and see if they differ at all. You might find that there are common pins, so beware.

    There are probably 4 separate windings on the secondary sire, so do the same.

    Then tell us what results you have.

    A far more likely source of problems is that one of the rectifiers has gone short circuit.

    Presuming the power supply has protection, this will result in the PSU shutting down, and that might be the fault you see.

    Pictures of the board and the transformer would be useful.
     
    Last edited: Aug 16, 2012
  7. whiskeycat

    whiskeycat

    8
    0
    Apr 11, 2012
    I'd like to help you on this one but what's the make and model no. of the tv? there's lots of places that I can search for a diagram for you. I assume this is the switching power transformer...you would need to find an exact replacement.
     
  8. shrtrnd

    shrtrnd

    3,665
    453
    Jan 15, 2010
    I'm still thinking your transformer is not the problem, as others here have noted.
    The transformer is the most expensive thing you'd be looking to replace, and you're
    going to be disappointed if it proves not to be the problem.
    I'd be checking the rest of the power devices on that tranformer board.
     
  9. whiskeycat

    whiskeycat

    8
    0
    Apr 11, 2012
    transformer

    I think I've only replace 1 or 2 of those during the years I worked in a repair shop..Problem is you need some test equipment...I just bought a ESR meter for capacitors from ebay. A bad cap will keep the power supply from working and the only way to test them is with a ESR meter.

    Another problem is there may be blown parts in the High Voltage section..even if you fix the power supply and then turn the set on parts could blow out again if you have something wrong in the high voltage section.
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Similar Threads
There are no similar threads yet.
Loading...
Electronics Point Logo
Continue to site
Quote of the day

-