Samsung ue49mu6120 No Standby

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  • Gjackson
    Senior Member
    • Aug 2021
    • 134
    • Malta

    #1

    Samsung ue49mu6120 No Standby

    Hi all,

    Have a Samsung ue49mu6120 with no standby light,
    unplugging mainboard cable from the power supply turns backlight on.

    power supply BN44-00807F
    Main board BN41-02568B​

    Some other users suggest that the 25Q40 EEPROM might have become corrupted,
    Could someone more knowledgeable take a look and see if mine is corrupted?

    Thanks in advance:

    Attached Files
  • Answer selected by Gjackson at 02-12-2025, 04:15 PM.
    nomoresonys
    Badcaps Legend
    • Jan 2013
    • 12090
    • U.S.

    Intermittent faults are tough ones if it was intermittent, could be what you soldered did it or maybe there was a bad connection that got better just by unhooking and re-hooking cables, guess just test it for a few hours and see.
    Last edited by nomoresonys; 02-12-2025, 04:00 PM.

    Comment

    • lotas
      Badcaps Legend
      • Jan 2016
      • 4524
      • Russia

      #2
      Your dump is working.

      Comment

      • Gjackson
        Senior Member
        • Aug 2021
        • 134
        • Malta

        #3
        Originally posted by lotas
        Your dump is working.
        Thanks Lotas,

        any clues how I should move forward and what to check next?
        For testing I have the mainboard and power supply on my bench connected to each other, it seems like 13v is being generated and the mainboard warms up slowly and then after a while it switches into standby mode 8v and I can't find anything wrong with either of them, 3.3v and 1.8v are generated. Right now I don't have the tv chassis to test with, but maybe the wifi module or t-con board is shorted and was shorting the power supply?

        Comment

        • nomoresonys
          Badcaps Legend
          • Jan 2013
          • 12090
          • U.S.

          #4
          Check voltages on CNM803, neg. probe on chassis ground, pos. probe on each pin, read tv in standby=plugged in but power off, take note, leaving probes where they are hit power button, take note of any change, can skip the grounds, report results.

          Comment

          • Gjackson
            Senior Member
            • Aug 2021
            • 134
            • Malta

            #5
            Originally posted by nomoresonys
            Check voltages on CNM803, neg. probe on chassis ground, pos. probe on each pin, read tv in standby=plugged in but power off, take note, leaving probes where they are hit power button, take note of any change, can skip the grounds, report results.
            Thanks for the reply, with the two boards set up on the bench here are the readings:

            Click image for larger version

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            while on standby:

            A13V = 8.9v
            FAIL_COUNT = 0v
            POWER_ON = 0.09v
            PWM_BLU = 0v
            OD_ON/OFF = 0v
            ANA_DIM = 0v

            while powered on:

            A13V = 12.8v
            FAIL_COUNT = 3.3v
            POWER_ON = 3.3v
            PWM_BLU = 0.04v
            OD_ON/OFF = 3.3v
            ANA_DIM = 0.08v



            I'm assuming pin 1 here spells out FAIL_COUNT because I can't really read it

            Click image for larger version

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            Comment

            • Gjackson
              Senior Member
              • Aug 2021
              • 134
              • Malta

              #6
              Interesting to note, if I unplug the mainboard from the power supply and take readings again it seems to fluctuate, I don't know if this is intended behavior from the power supply:

              A13V = Fluctuating
              FAIL_COUNT = 0v
              POWER_ON = Fluctuating
              PWM_BLU = Fluctuating
              OD_ON/OFF = Fluctuating
              ANA_DIM = 3.3v

              Here's the waveform for A13V when fluctuating:



              And for POWER_ON , PWM_BLU, OD_ON/OFF they all virtually look the same as this:



              A faint click can be audibly heard with every rise of the waveform coming from somewhere on the PSU​

              Comment

              • lotas
                Badcaps Legend
                • Jan 2016
                • 4524
                • Russia

                #7
                Fluctuations in power supply occur because there is no load at the output...Load it (13v) with a car incandescent lamp.

                Comment

                • Gjackson
                  Senior Member
                  • Aug 2021
                  • 134
                  • Malta

                  #8
                  Originally posted by lotas
                  Fluctuations in power supply occur because there is no load at the output...Load it (13v) with a car incandescent lamp.
                  The lamp lights up fine if the mainboard is also connected:

                  Click image for larger version  Name:	20250207_170801.jpg Views:	4 Size:	2.84 MB ID:	3566647


                  but when I disconnect the mainboard it blinks and doesn't remain steady:

                  Last edited by Gjackson; 02-07-2025, 10:16 AM.

                  Comment

                  • nomoresonys
                    Badcaps Legend
                    • Jan 2013
                    • 12090
                    • U.S.

                    #9
                    Diagnosing would be much easier if you had the whole tv.

                    Comment

                    • Gjackson
                      Senior Member
                      • Aug 2021
                      • 134
                      • Malta

                      #10
                      Just a quick update, I did exactly that and got the whole set to test with. Plugged everything back in and now it works somehow, I have standby and the tv powers on. I'm a little baffled as to why it's now working. Owner said that it was being intermittent but when I checked it there was no standby at all. There seem to be no cold joints and I tried tapping the boards while in operation and they seem to keep working. The only thing i've done is resolder the eeprom and replace the thermal paste on the CPU. Any clue as to what I should check before reassembly?

                      Comment

                      • nomoresonys
                        Badcaps Legend
                        • Jan 2013
                        • 12090
                        • U.S.

                        #11
                        Intermittent faults are tough ones if it was intermittent, could be what you soldered did it or maybe there was a bad connection that got better just by unhooking and re-hooking cables, guess just test it for a few hours and see.
                        Last edited by nomoresonys; 02-12-2025, 04:00 PM.

                        Comment

                        • Gjackson
                          Senior Member
                          • Aug 2021
                          • 134
                          • Malta

                          #12
                          I suppose so, in the meantime thanks everyone for the help!

                          Comment

                          • nomoresonys
                            Badcaps Legend
                            • Jan 2013
                            • 12090
                            • U.S.

                            #13
                            You are very welcome, never a problem helping decent people such as yourself.

                            Comment

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