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Capacitor replacement advice

Discussion in 'General Electronics Discussion' started by bwspot, Nov 25, 2013.

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  1. bwspot

    bwspot

    15
    0
    Nov 25, 2013
    I want to replace the capacitor on the power supply board for the samsung tv.
    Do the color matter for the capacitors or if i match the value all would be fine?
    I noticed there are few 1000uF 25V caps and 2 are dark purple and 1 is dark brown and their height is different, so i wonder if purchasing 3 same 1000uF 25V caps would work or i need the exact colors? See attached for the caps on the board.

    ATTACH]10561[/ATTACH]

    image 2.jpg
     

    Attached Files:

  2. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    Hi,

    The color doesn't matter, however the temperature range and the ESR does !
    better to find out the installed cap datasheet and to buy capacitor with (almost) the same ESR. Also don't buy chinese stuff on Ebay but go for brand like Panasonic on Nichicon at Mouser or Digikey.

    Olivier

    PS those caps don't look to have a problem, why do you suspect them?
     
  3. bwspot

    bwspot

    15
    0
    Nov 25, 2013
    The tv does not turn on. When i press the power button the power led blinks but tv does not power. 4 of the caps seems to be broken as they have black liquid at the top.
    the tv is samsung: Ln26a450c1d and power board is bn44-00208b
     
  4. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    Hi,

    The black trace are not coming from the caps, they are just marker trace done for any reason at the factory. Cap can have they top "poped" or have visible leak (almost transparent colored) or be dryed (no visible sign).

    Electrolytic capacitor is a common failure on TV's, can you post pics of all the power supply caps?

    Olivier
     
  5. bwspot

    bwspot

    15
    0
    Nov 25, 2013
    i will do it later once at home.
     
  6. shrtrnd

    shrtrnd

    3,821
    519
    Jan 15, 2010
    When you replace these caps, check the physical size/lead spacing.
    A few times now, I've not paid attention, and bought something that physically
    doesn't fit in the old board.
    Just something to be aware of.
     
  7. bwspot

    bwspot

    15
    0
    Nov 25, 2013
    yes i noticed the size is important. For example the board has 3 1000uF 25V caps but they differ in size, but descriptor on the cap itself is same.
     
  8. bwspot

    bwspot

    15
    0
    Nov 25, 2013
    board photos

    IMG_1876.jpg

    IMG_1878.jpg

    IMG_1879.jpg
     
  9. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    Capacitors looks OK. Did you check the fuse (located under the code bar)?

    Olivier
     
  10. bwspot

    bwspot

    15
    0
    Nov 25, 2013
    checked the fuse and it is ok
    i am not an expert but most forums were pointing to capacitors
    do they all have to blow to show that they are broken?
    can they look normal and still be broken?
     
    Last edited: Nov 26, 2013
  11. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    It's a common fault. It's probably worth looking at, even if it doesn't turn out to be the root cause.

    No, sometimes they look normal, yet have failed. This is not the common failure mode though.

    The real test is with an ESR meter. This will tell you for certain.

    Does the output of the power supply do *anything*? Is there a brief pulse of voltage at the output? It is highly unlikely that the power supply could detect failure of the caps without first turning on. It is possible that the power supply could then shut down because it sees some fault condition.

    What does the IC labelled as ICM801 have written on it? It is possible that the bootstrap power to this chip (assuming it is the main controller) has failed.

    Are there other chips on the other side of the board?

    Another fault condition that can cause a power supply to immediately shut down is a failure of one or more rectifiers on the output. This will cause a short overload that can sometimes be heard as a click coming from somewhere on the board before the controller shuts everything down.

    Beware that this power supply will have 400VDC on one of the caps and it can kill you when it's plugged in, and give you one hell of a belt even after it has been disconnected from the mains.
     
  13. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
  14. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
  15. bwspot

    bwspot

    15
    0
    Nov 25, 2013
    that seems scarry
    is it only the big one or small ones also?
    it this is dangerous maybe i should not even try?
     
  16. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    The capacitors storing the higher voltages are on the Hot side, see indication on PCB and on schematic. You can safely discharge them via a 470 ohms/ 2 watts resistor connected on alligator clips.
    The voltage rating written on the capacitor is a good indication of the maximum voltage you can almost expect.

    If you are nor comfortable with this repair don't do it or ask to a skilled person to zssist you (HAM, TV repair shop, Electronic club ...)

    Olivier
     
  17. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    They're all about the same.

    I don't like working with them.

    Half or more of them is at mains potential and without some skills with working with them, I'd not attempt trouble-shooting that requires tests while the power is applied.

    After the power has been applied, you need to be very careful to ensure you safely discharge the high voltage capacitors, or are *VERY* careful about keeping your fingers away from them.

    Being bitten by 400VDC from a capacitor is not something you'll soon forget.

    I am somewhat reluctant to offer too much advice because from looking at that circuit diagram, my next step would be to measure a voltage with the power applied (Vcc to the controller).
     
  18. OLIVE2222

    OLIVE2222

    690
    25
    Oct 2, 2011
    @Steve, I agree that giving remote repairing advice is not advisable here.

    However I fill that trashing a TV for few bad caps is bad for the environment (and the wallet). so a "statistical" (according to experience and google results on those TV's) repairing by replacing the caps worth the effort, yes doing measurements on powered TV IS NOT RECOMMENDED as this time is bad for the poster !

    @OP you can measure each capacitor with a multimeter in DC position to ensure that they are discharged

    Olivier
     
  19. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,497
    2,838
    Jan 21, 2010
    I agree.

    As I said, they're worth looking at.

    *carefully*!

    Holding both probes in one hand, or otherwise finding a way to only use one hand would be a good idea for the 400V capacitor!
     
  20. bwspot

    bwspot

    15
    0
    Nov 25, 2013
    capacitors i will be replacing are only 35V max, so i will just test if they are discharged and testing itself should discharge them. Put the board back and turn it on while all is assembled, so i wont be able to touch anything.
     
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