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EMERGENCY!!! Broken Samsung 42" Plasma HPT4254X/XAA

Discussion in 'Repairing Electronics' started by ben7, Oct 23, 2010.

  1. ben7

    ben7 Member

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    Our 42" Samsung plazzy stopped working today! First, it would turn on, warm up for a minute, then turn itself off!

    Now the power supply has been clicking on and off!

    Checked voltages once, 5V was 4.97v and 12 was 11.74.
    I have already checked the caps-none look bad.

    The supply steps up 120VAC to around 350 volts-that circuit is ok.
    The second part of the supply has 2 different smps's, they BOTH don't output any voltage even though the main control board is trying to turn the supply on with the standby +5volts.

    Any suggestions?
     

    Attached Files:

  2. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Samsung don't have a very good reputation for relaibility, and as far as I'm aware commonly don't supply circuits for most of their sets, you're supposed to replace entire PCB's. This policy means that they soon run out of replacement PCB's, and it's common for 18 month old sets to be obselete.
     
  3. killivolt

    killivolt Well-Known Member

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    I guess it would be a good idea for me to put on a Extended warranty or start saving for an entirely new set.

    If so, what is a good brand and bounce for my Buck $$$$$
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    My Philips made in Canada TV lasted for 26 years then my Sony made in Mexico TV lasted for 8 years.
    I have replacement slightly used Sony CRT TV that costed nearly nothing and is 6 years old. It might last another couple of years.

    My pc monitor is Korean made by Samsung and it still works fine after 5 years.

    30 years ago I saw some telephone systems made by Goldstar (a Korean company now called LG) and the soldering was horrible.

    My son and daughter have LCD TVs made by companies and in countries that I never heard of and they work fine after 2 years.
     
  6. RCinFLA

    RCinFLA Well-Known Member

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    Last edited: Oct 24, 2010
  7. ben7

    ben7 Member

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    After a lot of searching on the web I have found the problem.

    The problem is that a few mosfets are mounted together on a small heatsink-the 2nd from the left-and they typically run so hot over time they break down and eventually stop working.

    Checked them and 3 of them read open.

    Have bought replacements already but they will take about a week to get here.

    I am thinking of putting a [quiet] fan in the TV to circulate the air more.

    It's SO amazing that a small cheap part can cause something (worth thousands more) to break, and yet people just throw that stuff away!:rolleyes:
     
  8. ben7

    ben7 Member

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  9. ben7

    ben7 Member

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    Hmmm, even some stuff that is chinese or korean will last, you can tell by the price you pay and the company you get it from.

    I have an amazing little LG portable DVD player, the sound is nice and the screen has amazing quality! It right now is 3.5 years old, and works like a charm!

    A new laptop (cheapy one) that my mom got will not properly install anything on it; it tells you that the installation is corrupted!:confused:-LOL it is made by ACER and it has windows7.ACER IS the WORST computer company ever:mad::mad::mad:
     
  10. ben7

    ben7 Member

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    Oh, speaking of weird stuff a 32inch LCD made by Panasonic that we have will randomly beep.It's just a random, quiet beep from its speakers that will happen when the TV is on or off!

    seems to beep around quarter to eight at night.

    It is VERY weird!
     
  11. Jon Chandler

    Jon Chandler Banned

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    Randomly at 7:45? Must be a different definition than I am familiar with.
     
  12. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    The two top makes are Sony and Panasonic (at least in Europe), all others are a fair way behind on relaibility.
     
  13. ben7

    ben7 Member

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    Yes, Panasonic and Sony are the best!
     
  14. killivolt

    killivolt Well-Known Member

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    Thanks, I just didn't have the Money, they had a sale on at Sears. I should know that but, the Market tends to change rapidly and the only people who know are the ones working on them:)
     
  15. ben7

    ben7 Member

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    Yay!

    Got the parts today:D
    they are:

    2x 2200uf 25vcaps
    2x FQPF13N50CF mosfets
    2x FQPF9N50C mosfets

    Will be replacing them soon!:)
     
  16. ben7

    ben7 Member

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    Fixed!

    The old transistors had just about burnt thier thermal pads to nothing!
     
  17. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Well done - I'm pleased you got it sorted :D
     
  18. ben7

    ben7 Member

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    Thank you!
     
  19. WoR473

    WoR473 New Member

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    I'm having the same problem with mine but it will come back on after a while of clicking away...

    You plug it in and i may only click once or twice, then come one, or it may click for 10min and come on. Then once its on it may turn off in an hour and start clicking again, or it may stay on all night. Once it turns of and starts clicking, it eventually comes back on and the cycle repeats.

    Was this the same symptoms yours had? I tested the transistors and unless i tested wrong they appear to be good, but then again the tv still works *sometimes* so idk what it could be.

    I tested a few of the caps that i thought could be the culprit although none of them look bulged at all.

    Anyone have any ideas here? Can transistors be half bad and not just good/bad?

    Thanks!
     
  20. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    How did you test them? - you need either an ESR meter (test them non-powered) or a scope (test them powered up).

    Any other method and you haven't tested them at all.
     
  21. ben7

    ben7 Member

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    I did not have any bad caps in my TV, but they were CapXon which are not the best brand.

    The problem I had was some of the switching power transistors mounted on a big heatsink overheated, and failed.
    When they failed, the TV control circuit(running on the 5V sub)just kept trying to turn the power supply on, without success.

    Yeah mine started with clicking a little bit, but eventually coming back on, one day we tried to turn it on, and we got just a bunch of clicking.

    I suggest that you check the switching transistors.
    Take a look at the first picture in my first post of this thread.
    That is the power supply, the transistors to check are on the 2nd heatsink from the left, they are
    FQPF13N50CF mosfets, and
    FQPF9N50C mosfets

    hope we can get this sorted out for you! :)

    -Ben
     

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