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Samsung has 5v_STBY but no B13

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    Samsung has 5v_STBY but no B13

    Hi there!
    I have a Samsung UE32F4000 with a power supply model bn44-604F (L32SoE_DHS) and according to the owner, it gradually took longer and longer to turn on, until now that it won't turn on at all.

    Behaviour: Plug it in mains, led turns on. Push power button either on remote or physical pushbutton, led blinks once like trying to turn on, but after 2 seconds turns steady on again.

    Inside: I measured PS voltages. A5V measures 5.1v (expectable as I get LED on and remote signals have an effect) and when I try to turn on, I get B5V at 5.2v but B13V goes directly to 9v, quickly to 8v and then drops to 0 in under 1second

    I can't find the proper schematic for this PS but I tried swapping caps CM861 and CM855 (2 on top left corner in front side picture) and on first attempt I got BL to turn on for under 1 second but that was it, same behaviour again.

    I tried resoldering all the secondary leads of main transformer too.

    Any hint on to try next?
    Thanks
    Attached Files

    #2
    Re: Samsung has 5v_STBY but no B13

    Disconnect the cable from the power supply to the motherboard and turn it on, only the backlight should light up and check these 13v.

    Comment


      #3
      Re: Samsung has 5v_STBY but no B13

      Originally posted by lotas View Post
      Disconnect the cable from the power supply to the motherboard and turn it on, only the backlight should light up and check these 13v.
      Ok I just checked this.
      BL turned off. But I checked B13v and it measured steady 8,2V. Also measures Vamp (not sure what this is) and also got 8.2V (probably jumpered to B13v)


      Also while doing this test, after some minutes having the TV on with MAIN board cable off, the backlight started flickering and finally turned off by itself. Then later on it turned on again...

      If only I could find an schematic for this PS I guess I would see what feeds the B13V pin....

      Comment


        #4
        Re: Samsung has 5v_STBY but no B13

        Also, while I manage to get a proper schematic, I see only 4 capacitors nera the secondary side of the tansformer and close to the outputs socket. They give out these voltages:
        1.- 142v. This has to be for led strips
        2.-5.2v This has to be A5v
        3.-14V this has to be A13v
        4.- 8.8V this has to be B13V

        What happens if I jumper 14V to 8.8V and see if it turs on?
        Does this make sense?

        Thanks

        Comment


          #5
          Re: Samsung has 5v_STBY but no B13

          There is nothing to bridge, these are different voltages, Vamp is the voltage for powering the audio frequency amplifier on the motherboard.

          Comment


            #6
            Re: Samsung has 5v_STBY but no B13

            Originally posted by lotas View Post
            There is nothing to bridge, these are different voltages, Vamp is the voltage for powering the audio frequency amplifier on the motherboard.
            No, no... You misunderstood me. I was wondering if Vamp is the same voltage as B13V but I don't really care much for that now

            My question is, according to other alike schematics, there's a 13V voltage present at the "input" of a mosfet that is driven to B13V whenever the mosfet Gate is ON. I do get 14V on one capacitor, probably driving the input to that mosfet, and I get only 8V at the output of that mosfet, not sure if because the mosfet is faulty, or the driving voltage at Gate is inssufficient.

            Can I just jumper Source to Drain in this mosfet and see if this 14V goes straight to B13V and powers up the TV? I mean temporarily to see if the issue is here...

            Thanks

            Comment


              #7
              Re: Samsung has 5v_STBY but no B13

              See the lower section of this file, the one that runs thru B13V. I found that MOsfet and it has 13.? V at its Drain and only 8.x V at its SOURCE

              https://elektrotanya.com/PREVIEWS/po..._sch.pdf_1.png

              Comment


                #8
                Re: Samsung has 5v_STBY but no B13

                8v at the output is usually when the power supply is in standby mode, and when switching to work, these 8v rise to 13v.

                Comment


                  #9
                  Re: Samsung has 5v_STBY but no B13

                  Not this one, this one was close to 0V when off and jumped up to 9 then 8v when it was turned off

                  Comment


                    #10
                    Re: Samsung has 5v_STBY but no B13

                    Im reading that this TV has a specific protection that drives PS_ON to low when the LED DRIVER feels overcurrent or open circuit. Could it be that the led strip has one led shorted so the current is above a certain threshold and the PS_ON gets shorted to ground, therefoe opening the mosfets that drive the B13V voltage?

                    Comment


                      #11
                      Re: Samsung has 5v_STBY but no B13

                      Service manual
                      Attached Files

                      Comment


                        #12
                        Re: Samsung has 5v_STBY but no B13

                        Originally posted by lotas View Post
                        Service manual
                        Thanks, I checked it and all it says is "if no A5v and no B5v, then change cable from PS to main"
                        In my case I do have B5v and the issue is not the cable as Im.checking the PS board alone

                        Comment


                          #13
                          Re: Samsung has 5v_STBY but no B13

                          Originally posted by edugimeno View Post
                          Im reading that this TV has a specific protection that drives PS_ON to low when the LED DRIVER feels overcurrent or open circuit. Could it be that the led strip has one led shorted so the current is above a certain threshold and the PS_ON gets shorted to ground, therefoe opening the mosfets that drive the B13V voltage?
                          This sounds very logical, do you have a way to test the backlights?

                          Comment


                            #14
                            Re: Samsung has 5v_STBY but no B13

                            Originally posted by nomoresonys View Post
                            This sounds very logical, do you have a way to test the backlights?
                            Not really, I see they do work as if I unplug the PS-to-MAIN cable it lights up, but I can't see if there's a blown LED in the whole set
                            Option 1: Remove LCD panel and check visually (or check individually if they have pads), with the risk involved of damaging the panel....
                            Option 2: Measure current in the BL line, but how do I find out the expected current?

                            Thanks

                            Comment


                              #15
                              Re: Samsung has 5v_STBY but no B13

                              Voltage and current are marked on the power supply.

                              Comment


                                #16
                                Re: Samsung has 5v_STBY but no B13

                                Originally posted by diif View Post
                                Voltage and current are marked on the power supply.
                                Oh...you are absolutely right. Sorry for that. I will check that today
                                Thanks

                                Comment


                                  #17
                                  Re: Samsung has 5v_STBY but no B13

                                  Ok I checked something else.
                                  There is a mosfet that drives the 13V from the rectifier after the transformer to the B13V pin when there's a high signal in PS_ON. This all makes sense.
                                  I measured voltages at this mosfet: Source: 14V (close to expected), Gate 12V (meaning: "GO") and drain has 9V, when It should have 13V.
                                  I have checked other equivalent mosfets on this board that are in ON state and they drop close no 0V from Source to Drain, and this one drops 5V.
                                  I think either the mosfet is bad, or whatever is driven from it is in short
                                  Does this make sense? Anything to start with?

                                  Thanks

                                  Comment


                                    #18
                                    Re: Samsung has 5v_STBY but no B13

                                    Ups... I screwed up big time....
                                    The owner reminded me that I already fixed this TV for him some months ago and what I did was redoing some solder joints
                                    So leaving aside all my previous asumptions I redid a lot of solder points and VOILA! The TV turned on! I could see a "no signal" box floating around the screen, while I was holding the set upside down leaning it. At this time I forgot that the PSU board was not screwed yet to the chassis, so this board slipped off to one side and created a spark that turned everything off....
                                    Turned back on again and now I got the correct voltages B13v, etc (12.5v) but the backling it flickering at extremely dim, like 5% of its normal brightness. The BL voltage has increased 20 volts (From 165 to 185v).
                                    I removed the panel, and went ahead to all led strips checking them all individuallywith their test pads to realize ALL leds have blown out... Not one or two, ALL leds
                                    I need to buy new led strips now and see from thete what's missing...

                                    Comment


                                      #19
                                      Re: Samsung has 5v_STBY but no B13

                                      Samsung UExxFxxxx - has always suffered from LEDs (not a power supply upgrade, LEDs work at the limit).

                                      Comment


                                        #20
                                        Re: Samsung has 5v_STBY but no B13

                                        Ok, but not this case. Read my last post. I redid some solders in the PSU board and it started to work 100% perfectly until MAX voltage to the LED strips and fried them all at the same time.

                                        Comment

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