LCD TV Inverter Board Repair

Discussion in 'Technical Repair' started by Mad Professor, Jun 3, 2009.

  1. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    Good Day All.

    I have a Matsui LM20N2 LCD TV that has a problem with the power / inverter board.

    I have been trying to repair this TV on and off since Sep 2008, but I don't have a grate deal of free time, so it's just been put in the cupboard collecting dust.

    I did make a post on the eserviceinfo.com forum last year, that post can be found here: Matsui LM20N2 LCD TV - Service Manual or Schematics.

    Right down to the problem.

    If you power the unit on by the wall socket the stand-by LED will light up, If you then press the power button on the unit it will power up for a max of a second and then go back into stand-by.

    I have taken the covers of the back on the unit, and the inverter is apart of the main power board.

    If I remove Q7, Q8, Q9, Q10, Q11, Q12, Q13, Q14, witch are all the same, the TV will fully power up, and stay on with sound, and if you get the light just right you can make out a picture.

    [​IMG]

    Q11, Q12 have failed as they are burnt.

    Also one of the two blue caps in the middle of the picture had split.

    Q7 - Q14 have thease markings.
    H. SD
    965
    56 HR

    So it should be a HSD965 NPN Epitaxial Planar Transistor.

    The two blue caps C6 & C7 are marked as.
    F .27J
    PMD 250V

    So is should be a 0.27uf (270nf) 250v cap.

    So after replacing the parts the TV still fails to come out of standby so there has to be somthing else worng.

    Please can you help and advice how to track down what else might be at fault.

    Thanks for your time.

    Best Regards.
     
  2. S_lannan

    Active Member

    Jun 20, 2007
    247
    2
    the actual back light itself could be at fault.
    perhaps one of the inverter transformers has shorted turns?
     
  3. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    So what happened when you tested the transistors?
     
  4. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    I never bothered with the transistors as two of them where burnt, as it in it had burnt a hole in the transistor it's self.

    I don't think it's a problem with the back light it's self as you can disconect the back lights from the PCB and the tv will still fail to come out of stand-by.

    Is there any easy way of testing if the back lights are ok?

    I am more pointing at one of the inverter transformers has failed.

    The markings on the inverter transformers are.
    SPI 8TJ00013
    0542 1 FC GP
     
    Last edited: Jun 3, 2009
  5. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    I have just removed all four of the transformers from the PCB.

    The output side has 4 pins but only two are used, and all of the transformers read from 312-314ohms.

    The input side of the transformers have multipole legs and inputs.

    Input side of the transformers reads,
    Pin1+6 = 00.3 - 00.4ohms.
    Pin2+3 = 00.3 - 00.4ohms.
    Pin4+5 = 00.3 - 00.4ohms.

    I have half tested the four back lights each in turn with a inverter from an old dead laptop, The inverter I used only has an output of around 600vac and the output of the units inverter is ment to be around 1500vac, so the tubes did not fully light but was able to see that all part light and look the same.
     
    Last edited: Jun 3, 2009
  6. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    Is anyone able to help or advice me on what I should test or how to go about testing it.

    Thanks for your time.
     
  7. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    A functional transformer will pass a signal from signal generator, visible on a scope.

    Try 50Khz - 150 Khz
     
  8. asbesto

    New Member

    Sep 4, 2009
    2
    0
    Hi,

    I have a similar problem on the SAME board, on a Nordmende LCD TV set! It's the same inverter board, and I have two exploded HSD965 transistors.

    My problem is that I can't find any cross reference to change those transistors. Can someone help me giving me some similar transistor that can I use and purchase, maybe online?

    p.s. my tv set will turn on and seem working, but no retroillumination at all. I can see images using a lamp on the screen! :)
     
    Last edited: Sep 4, 2009
  9. Mad Professor

    Thread Starter Active Member

    Apr 15, 2009
    133
    1
    If you are in the UK you can get "2SD965" from CricklewoodElectronics.

    I have not yet got round to ording any new parts yet.

    If you get your unit working again please let me know what parts you ended up replacing.

    Best Regards.
     
  10. asbesto

    New Member

    Sep 4, 2009
    2
    0
    Thank you, I can find them on Ebay! ;)
     
  11. Perfectboy

    New Member

    Sep 9, 2009
    9
    0
    Hi, i think it's still the problem of your transistors.
    [​IMG]
     
  12. Herman Munster

    New Member

    Oct 25, 2010
    1
    0

    Hey, Mad Professor, are you still working on this project? If so, make sure you have a signal going to the tv for it to read. I had the same problem, I just got this from my father-in-law, he was going to take it to recycling but I convinced him to let me look at it. first I tried to duplicate what he said was wrong with it: sound but no picture. I saw online that it could be the back light after punching up a quick google search. I plugged it in to my laptop as a secondary monitor and presto, the light changed to green and tilting the screen at an agle to catch bright external light, the picture was very faintly duplicated. My board looks identical (down to the last detail) of the picture you posted except mine is not mising the two transistors. The capacitor is even split in the exact same way as descernable on your pic. The transistors so not seem to have any visible damage to them. there is a slight discoloration on the board that seems to track along in the same direction as the transistor row but I consider that may have been made in assembly as the resin sealent on these boards, post-assebly, can have a discolored apearance even on perfectly working boards.

    For now I'm not going to mess with the transistors. I am going to replace the .27j 250v caps and see if that springs her back to life. If you have replaced this/ese cap(s) already, have you attached it to a signal?

    what if anything changed in display or symtoms?

    if nothing, did you try different signal sources?
     
  13. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,750
    760
    I think he has already quit, and bought a new one.
     
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