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Samsung UE49MU6105K - boot loop, horizontal lines

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    Samsung UE49MU6105K - boot loop, horizontal lines

    Less than a year out of warranty, samsung UE49MU6105K craps out, they've got this designed obsolescence down to an exact science of self destruct when out of warranty...

    Screen started to show horizontal lines and ghosted image at the bottom, then turned off by itself. Did software update, to no avail of the line problem, and got a boot loop after some minutes of watching TV. This boot loop will turn on the backlights for some seconds the sound comes on, the image will turn dark very fast and then it reboots again. Pressing power button will not put it on standby. Disconnecting power to main board allowed backlight to stay on. Left it disconnected for a while and then tried powering up. Still got the horizontal lines, but less than initially, a pronounced line plus some fainter ones. At this point I noticed the whole screen had a staircase degradé/dithering, when watching closely, looks like a bad inkjet print where you can see the dithering and spacing/lines between the printed rows. On the right side of the screen an inch/couple of cm above the bottom a lighter spot that is hot to the touch (no other spot on the screen is this hot) is where the problem seemed to originate (I expected a burnt COF or something) but I disassembled and peeked under this side and there's no tabs or other components on the right side of the screen, only at the bottom that I could see. Is a short inside the panel, apart from breaking it, even possible?
    Left unplugged overnight as the mainboard was making some electrical noise (not sure if it was always there with the back side fitted). When turning back on the next morning got the boot loop again. Tried the "quick fix" taped pins 4 to about 14 on the first flat cable this seemed to had fixed the "boot loop" problem. Taping some of the last pins on the second cable eliminated the black line, still some almost unnoticeable lines (and the whole screen staircase dithering) remained.
    This wouldn't be too bad, but next morning just a boot loop again... so the taping didn't really "fix it"


    Nothing looks obviously burnt or bulged. The power board voltages look ok, 12v , 3.3v ... tried disconnecting the PWM BLU pin but basically still a longer cycle boot loop (someone used this to fix another samy to have backlight always on)

    The lower board with the integrated T-con and tabs/COFs to the screen visually looks good, nothing obviously burnt. All the SMD resistors show open circuit or very low ohm, like 20. Many cases on youtube where bad resistors have closed circuit and replacing them plus removing some overcurrent SMD fixes it.

    The voltage though I got 7.5v and 15v on some, when this board is marked VSS - 7.6 and VOFFE_-11v but found another marking with AVDD 17v... so not sure if this is a problem.

    sticker on mainboard:
    UE49MU6100WXXN
    BN94-1243B

    MOEDL (sic) : KANT_M_BUILT_IN
    CODE: BN41-02568B
    MODEL: BN41-02568
    SIZE: 193X241 1.6t
    Date:2017.03.20

    sticker near power board:
    BN96 - 44229A NO REV
    BN96 - 44229A SHC "B"
    49" MU 6100 22.2.2018

    sticker near LED connector:
    CY-GM049HGLV1H
    BN95-04219A
    SK09BN9504243AS001K310544
    Made in Slovakia 49A6AU0VM


    markings on tabs/COF circuit board:
    dynamic KM1-V0
    E255400 94V-0
    16Y VU49SR4LV0.1

    stickers on tabs/COF circuit board:
    8GHL3J0E0A 1752
    LSF490FN02-L15
    BN96-39044A

    T36123D7LIRZ6
    22205C
    VNB U60F

    markings on powerboard:
    L55S6R_MHS BN44-00807F
    sticker: CN07BN4400807FAM5RJCI5399 R.B


    All help is much appreciated.
    Attached Files

    #2
    Re: Samsung UE49MU6105K - boot loop, horizontal lines

    Had the chance to sit down and take note of the voltages and resistance

    With the main board disconnected from the power board and turning the TV on (backlight stays on) I measured the following voltages on the CNM803 connecter:

    #by row sequence/ # and name in schematic
    1/1 Fail count- 0.08v
    2 to 5/ 3,5,7,9 (A13V)- 12.91v
    6 / 11 (GND)- 0v and 0.08 ohms

    7/2(ANA DIM)-2.74v
    8/4(OD ON/OFF)-3.61v
    9/6(PWM BLU)-3.09v
    10/8(POWER ON)-3.24v
    11/10(GND)-0v and 0.07 ohm
    12/12(GND)-0v and 0.07 ohm

    With the mainboard connected to the power board (and one LVDS flat cable disconnected so the boot loop wouldn't strike) I read 3.38v on pin 1 (0.08v when mainboard disconnected from power board per above) the rest on the top row remaining the same, don't know how to read the bottom row pins when the connector is inserted.

    So on the mainboard with the bottom cable, that feeds the right side of the screen from viewing position (left side seen from the back) , disconnected I proceeded to read the driver board on the right side (the one that is still connected to the mainboard with the top LVDS cable). I believe this model won't send any information if one of the LVDS cable is disconnected, so the readings I got were close to 0V and 1.8V on some SMD.
    Then swapped the cable that was disconnected, leaving the bottom one connected (goes into left side driver board seen from the back). Again same readings.
    Then connected both cables and the TV didn't cycle/boot loop, but it seemed to remain black image (backlights always on), so turned off and on again and the image was back, for some reason... remember I have no tape cutting out LVDS pins at this moment.

    So it seems the TV (mainboard?) needs to heat up to make the boot loop go away, and doesn't get a chance to heat up because of the boot loop, and leaving it on with just one LVDS cable allows it to heat up.

    So I proceed to take readings on the driver board again, now with image on screen. On the top most left most SMD capacitor (brown) on the left driver board (the one I suspect is creating the hot spot defect on the right side of the screen in viewing position), reads -9.59V on the top side and 0 on the bottom side. The SMD resistor (black) right next to that one reads 5.8V on top and nearly 0V on bottom side. The next capacitor reads 7.49V on the bottom side and 0V on the top side. Next resistor reads nearly 0V and the next one 1.8V on the bottom side and 0V on the top side. Some more with 0V , 1.8V, 7.49V then two with 14.99V, 7.49V again ... I will organize a table and scheme if that is helpful, but those are the values I got across the driver boards. (note: made a mistake: attachments have resistor/capacitor names swapped, files named resistor should read capacitor and vice-versa)

    Left it off for 20 minutes and when turning on it's in a boot loop again with the image quickly going dark and power cycling.

    Didn't get the chance to read the voltage on the right most SMD on the right side driver board, but isn't -9.59V weird on the left side?

    Any ideas?
    Attached Files
    Last edited by blaster_; 06-23-2022, 05:09 PM.

    Comment


      #3
      Re: Samsung UE49MU6105K - boot loop, horizontal lines

      with tv unplugged from power, unhook panel driver board from mainboard, check the caps on panel driver board for shorts, can also check them for low ohms.

      Comment


        #4
        Re: Samsung UE49MU6105K - boot loop, horizontal lines

        if this tv has a stand alone tcon unhook panel driver board from tcon.

        Comment


          #5
          Re: Samsung UE49MU6105K - boot loop, horizontal lines

          Thanks, will do tomorrow. The resistance readings I did on the driver board were with the cables connected. Will do a thorough reading with cables disconnected. I've read these are in series and it's hard to pinpoint the shorts. Hope to get some clues that it's definitely a driver board problem before having to make permanent alterations to a board that basically can't be swapped (don't worry I'm not cutting the COFs )

          edit: there's no standalone t-con, just power BN44-00807F, main board BN41-02568 and driver board/integrated t-con: dynamic KM1-V0 E255400 94V-0

          the inside looks pretty much like this R series model:
          https://www.youtube.com/watch?v=AoFacR3t6ag
          Last edited by blaster_; 06-23-2022, 05:50 PM.

          Comment


            #6
            Re: Samsung UE49MU6105K - boot loop, horizontal lines

            yes the one that's shorted can be hard to find without a milliohm meter, I find that a lot of times it's one of the end ones.

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