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    Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

    I have a Samsung LN32B360C5D set that has a mind of its own. Its like the little girl who when she was good she was very, very good but when she was bad she was horrible. If it hasn't been plugged in for a while -- a few hours to a few days -- it acts like it should. ...for a while... The standby light comes on and it responds correctly to all the side panel buttons as well as the remote control and has a great picture. However, either after turning it off or after it has been on 10-15 minutes, when you turn it back on it is in a 28-29 second perpetual loop -- power-on chime, 1.5-2 sec backlights on, 28-29 seconds backlight goes off, 1.5-2 seconds later you hear the power-on chimes and it just repeats. Once it starts looping none of the controls, button or IR, have any effect -- it just loops on its own and will start looping as soon as the power cord is plugged in.

    All the voltages look good. In fact, even when it is not responding to the buttons and IR they are still sending correct signals to the main board. The only difference I have found that correllates to when it works and when it doesn't is the pin coming from the chip under the finned heat sink on the main board -- I haven't been able to find a schematic of the main board -- that switches on the pull-down transistor Q302 for pin 1 (power on/off) works correctly when the set is working correctly but just sits at 0V when it isn't. 0V leaves the pull-down off letting pin one go high which is the on signal.

    I have an oscilloscope but don't really have the correct probes for looking at ripple noise on a switching PSU so I can't say that the power rails are completely clean. Just in case I re-capped the whole thing with capacitors of the correct voltage, capacitance and low ESR but it made zero difference in the symptoms. I do see the high voltage frequency/duty cycle change when the power-on chimes and then when the backlight comes on and again when the backlight goes off. No way for me to know which comes first but since the PSU uses PWM it appears that it is working correctly and these are just the changes that result from feedback from the various loads but probably primarily the inverter load.

    Since the voltages and inputs look fine, just the one output line that doesn't always seem to be working, I'm thinking of removing the glued-on heat sink and reflowing the solder on the chip that contols that on/off signal but before I do I thought I would run this by folks to see if there might be some better approach. I would love to be able to find a schematic of the main board but either my google skills are insufficient or there just simply isn't one online anywhere.

    Thanks in advance for whatever help and advice you might offer,

    Howard
    Attached Files
    Last edited by Howard_Woodard; 01-08-2020, 02:35 PM.
    Howard
    Seattle, WA

    #2
    Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

    While I'm waiting for any replies I'll add some additional info...

    (1) When CN802 is unplugged the backlight comes on as soon as the power cord is plugged in and stays on. I think that's what it's supposed to do.

    (2) With CN802 connected, if I ground pin 1 before plugging the power cord in it does not auto-start and the voltage at CP815 is 165-170 vdc. As soon as I remove the ground on pin 1 the voltage steps up to 390 vdc.

    (3) When the power plug is first connected the voltage at CP815 goes to 160 where it stays for less than a second before stepping up to 390 vdc.

    (4) I disconnected the keyboard and then disconnected the cable between the IR receiver and the main board. It didn't change anything - TV continued to loop start.
    Last edited by Howard_Woodard; 01-08-2020, 04:40 PM.
    Howard
    Seattle, WA

    Comment


      #3
      Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

      Can we see good clear pictures of the whole backside of the TV showing all the boards?
      Also good clear pictures of the main board.
      Never stop learning
      Basic LCD TV and Monitor troubleshooting guides.
      http://www.badcaps.net/forum/showthr...956#post305956

      Voltage Regulator (LDO) testing:
      http://www.badcaps.net/forum/showthr...999#post300999

      Inverter testing using old CFL:
      http://www.badcaps.net/forum/showthr...er+testing+cfl

      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
      http://s807.photobucket.com/user/budm/library/

      TV Factory reset codes listing:
      http://www.badcaps.net/forum/showthread.php?t=24809

      Comment


        #4
        Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

        Sure thing. Thanks for your interest...
        Attached Files
        Howard
        Seattle, WA

        Comment


          #5
          Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

          So when it acts up, the PS-on keeps swinging hi-lo in-sysc with boot loop, correct? How about the BL-ON signal, is it also swinging hi-lo also?
          Does heating the main board have any affect?
          Service manual:
          https://elektrotanya.com/showresult?...oria=&kat2=all
          Never stop learning
          Basic LCD TV and Monitor troubleshooting guides.
          http://www.badcaps.net/forum/showthr...956#post305956

          Voltage Regulator (LDO) testing:
          http://www.badcaps.net/forum/showthr...999#post300999

          Inverter testing using old CFL:
          http://www.badcaps.net/forum/showthr...er+testing+cfl

          Tear down pictures : Hit the ">" Show Albums and stories" on the left side
          http://s807.photobucket.com/user/budm/library/

          TV Factory reset codes listing:
          http://www.badcaps.net/forum/showthread.php?t=24809

          Comment


            #6
            Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

            When it is acting up the PS-On signal stays right at the 1.7vdc - never changes. The base voltage stays at zero so Q302 never turns on.

            BL-On signal tracks right with the Backlight going on and off.

            I never tried heating the mainboard but I will.

            Thanks for the SM link. I don't know why it never showed up on any of my google searches.
            Howard
            Seattle, WA

            Comment


              #7
              Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

              Originally posted by Howard_Woodard View Post
              When it is acting up the PS-On signal stays right at the 1.7vdc - never changes. The base voltage stays at zero so Q302 never turns on.

              BL-On signal tracks right with the Backlight going on and off.

              I never tried heating the mainboard but I will.

              Thanks for the SM link. I don't know why it never showed up on any of my google searches.
              So it is the BL-ON control signal issue.
              Never stop learning
              Basic LCD TV and Monitor troubleshooting guides.
              http://www.badcaps.net/forum/showthr...956#post305956

              Voltage Regulator (LDO) testing:
              http://www.badcaps.net/forum/showthr...999#post300999

              Inverter testing using old CFL:
              http://www.badcaps.net/forum/showthr...er+testing+cfl

              Tear down pictures : Hit the ">" Show Albums and stories" on the left side
              http://s807.photobucket.com/user/budm/library/

              TV Factory reset codes listing:
              http://www.badcaps.net/forum/showthread.php?t=24809

              Comment


                #8
                Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                How would that cause the TV to turn on automatically? Are you referring to a known BL-On issue or are you saying that it appears to be a BL-On issue? I can't tell if the BL comes on/off before or after the signal changes.
                Last edited by Howard_Woodard; 01-08-2020, 06:35 PM.
                Howard
                Seattle, WA

                Comment


                  #9
                  Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                  PS-ON is for turning on the rest of the power supply, so when the unit in the boot loop but the PS-ON is still steady, then the PFC Boosted Voltage on the main cap should also be steady, same for the switched 12V. Is'n that what you are seeing?
                  BL-ON is for turning on the inverter circuit and it keeps changing state when the TV acts up.
                  Last edited by budm; 01-08-2020, 06:47 PM.
                  Never stop learning
                  Basic LCD TV and Monitor troubleshooting guides.
                  http://www.badcaps.net/forum/showthr...956#post305956

                  Voltage Regulator (LDO) testing:
                  http://www.badcaps.net/forum/showthr...999#post300999

                  Inverter testing using old CFL:
                  http://www.badcaps.net/forum/showthr...er+testing+cfl

                  Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                  http://s807.photobucket.com/user/budm/library/

                  TV Factory reset codes listing:
                  http://www.badcaps.net/forum/showthread.php?t=24809

                  Comment


                    #10
                    Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                    When it gets plugged in the main voltage very briefly goes to 160vdc but approx <1 sec later the voltage jumps on up to 390vdc at the same time that the BL and BL-On comes on. At that point the PS-On is 1.7vdc and never changes again. The 5vdc and 13vdc rails are steady. Then, approx 30 seconds later the BL-On signal and the BL appear to drop simultaneously. Approx 1 sec later the Power-On Chime sounds followed by a repeat of all of the above. From that point on it appears that the BL-On signal is the only voltage that changes. It will repeat this loop with no variability forever - every 28 seconds.
                    Last edited by Howard_Woodard; 01-08-2020, 06:54 PM.
                    Howard
                    Seattle, WA

                    Comment


                      #11
                      Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                      It sounds like the power-chime and BL-ON are not related to PS-ON since it never change state, main board micro controller did not power cycle the power board when the TV acts up..
                      Try heating and cooling the board and see what happen.
                      It does not seem to be EEPROM either.
                      https://www.shopjimmy.com/samsung-ln...eprom-only.htm
                      Never stop learning
                      Basic LCD TV and Monitor troubleshooting guides.
                      http://www.badcaps.net/forum/showthr...956#post305956

                      Voltage Regulator (LDO) testing:
                      http://www.badcaps.net/forum/showthr...999#post300999

                      Inverter testing using old CFL:
                      http://www.badcaps.net/forum/showthr...er+testing+cfl

                      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                      http://s807.photobucket.com/user/budm/library/

                      TV Factory reset codes listing:
                      http://www.badcaps.net/forum/showthread.php?t=24809

                      Comment


                        #12
                        Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                        Yes, I'll try heating and cooling the main board and will report back.

                        Since the chip under the finned heat sink on the main board is the one that controls the base voltage for Q302 which turns the PS-On signal on and off and it is not varying, even though the inputs (kybd and IR) are, what do you think of my idea of removing that heat sink and reflowing the solder for that chip? When the TV chooses to tease me with a short time of working that signal turns on/off (controlling Q302) just as you would expect each and every time that the side button or the remote power is pressed.
                        Howard
                        Seattle, WA

                        Comment


                          #13
                          Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                          Q302 is for PS-ON and it has nothing to do with BL-ON.
                          When you run the power supply board by itself, the backlights come on and stay on as long as the the board gets the AC power then the power supply board is OK, the power supply board has pull-up resistors to simulate control signals for self test.
                          Last edited by budm; 01-08-2020, 07:16 PM.
                          Never stop learning
                          Basic LCD TV and Monitor troubleshooting guides.
                          http://www.badcaps.net/forum/showthr...956#post305956

                          Voltage Regulator (LDO) testing:
                          http://www.badcaps.net/forum/showthr...999#post300999

                          Inverter testing using old CFL:
                          http://www.badcaps.net/forum/showthr...er+testing+cfl

                          Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                          http://s807.photobucket.com/user/budm/library/

                          TV Factory reset codes listing:
                          http://www.badcaps.net/forum/showthread.php?t=24809

                          Comment


                            #14
                            Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                            Thanks for helping me. Let me test my understanding here...

                            The TV gets plugged in and only the standby power should be on. Q302 should have a +vdc on its base, forward biasing it and pulling its collector (pin 1, PS-On) to ground (0vdc). When the keybd or remote on buttons are pressed that chip under the heat fin detects it and, along with whatever else it needs to do, it drops the voltage on the base of Q302, turning it off, causing the 5vdc through a pullup on the PSU to forward bias QM802 turning on the rest of the power supply -- including power to the processor which boots the TV up.

                            Now that we're up, what, besides over-current, would cause the BL-On to switch off? And if its over-current, how likely is it that it would repeat to possibly the millisecond? And if its over-current than why does it work after long periods disconnected and seems like it would just keep on working so long as it was never turned off?

                            Please don't get me wrong, I'm not challenging anything you're saying -- I'm just sharing the experience I have had with it the best that I can.

                            I'll try the heat gun right after supper and will let you know what happens.

                            Howard
                            Howard
                            Seattle, WA

                            Comment


                              #15
                              Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                              "The TV gets plugged in and only the standby power should be on. Q302 should have a +vdc on its base, forward biasing it and pulling its collector (pin 1, PS-On) to ground (0vdc). When the keybd or remote on buttons are pressed that chip under the heat fin detects it and, along with whatever else it needs to do, it drops the voltage on the base of Q302, turning it off, causing the 5vdc through a pullup on the PSU to forward bias QM802 turning on the rest of the power supply -- including power to the processor which boots the TV up." That is correct.

                              Some TV will use error signal from the backlights circuit to provide error the feedback to the main board so it will shutdown the BL-ON control line.
                              Your power supply/inverter board BN44-00289B has backlights error signal pin (DET-5V), the main board may or may not use this error signal in the your TV model.
                              The backlights inverter circuit has protection circuit that detect open lamp circuit, or over current protection circuit which will shutdown the backlghts circuit.
                              So far the self test of the power supply/inverter seems to indicate that it is OK.
                              See the attached PDF of the power supply/inverter circuit.
                              Strange part is that the TV keeps reboot itself without power cycle the PS-ON line. Are you 100% sure that PS-ON never changed state when the TV reboots itself?
                              Attached Files
                              Last edited by budm; 01-08-2020, 07:55 PM.
                              Never stop learning
                              Basic LCD TV and Monitor troubleshooting guides.
                              http://www.badcaps.net/forum/showthr...956#post305956

                              Voltage Regulator (LDO) testing:
                              http://www.badcaps.net/forum/showthr...999#post300999

                              Inverter testing using old CFL:
                              http://www.badcaps.net/forum/showthr...er+testing+cfl

                              Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                              http://s807.photobucket.com/user/budm/library/

                              TV Factory reset codes listing:
                              http://www.badcaps.net/forum/showthread.php?t=24809

                              Comment


                                #16
                                Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                                Ok, thanks. Before I try the heat I'll put my scope on DET-5V and see what it does through the cycle.
                                Howard
                                Seattle, WA

                                Comment


                                  #17
                                  Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                                  DET-5V...

                                  Plug power cord in and pin 14, DET-5V, goes to about .5vdc and after approx 1/2 sec it goes to .7vdc -- could be a diode or an emmiter-base junction. The startup Chime is heard and it goes to 4.88vdc. It stays steady until it, BL-On and the BL all drop off about 28 seconds later. Then, like the rest of the system, it repeats predictably.
                                  Last edited by Howard_Woodard; 01-08-2020, 08:59 PM.
                                  Howard
                                  Seattle, WA

                                  Comment


                                    #18
                                    Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                                    I see that I didn't answer one of your questions. Yes, I put my oscilloscope on the PS-On line to see if I could see anything that my VOM wouldn't detect. The PS-On line is a steady 1.7vdc. I also monitored the base of Q302 and it was a steady 0vdc the whole time. I have followed the trace back from the base of Q302 to a pin on that chip beneath the finned heat sink. There is nothing in between, including any components such as caps that could short that line to ground. Unless the heat gun gives us some additional info or someone comes up with some other things to test it's beginning to look like reflowing the solder on that chip should be our next step.

                                    Agree?
                                    Last edited by Howard_Woodard; 01-08-2020, 08:31 PM.
                                    Howard
                                    Seattle, WA

                                    Comment


                                      #19
                                      Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                                      If you run the power supply board by itself, I expect the DET-5V to be high when backlights are staying on and it should go low if the protection circuit kicks in.
                                      Never stop learning
                                      Basic LCD TV and Monitor troubleshooting guides.
                                      http://www.badcaps.net/forum/showthr...956#post305956

                                      Voltage Regulator (LDO) testing:
                                      http://www.badcaps.net/forum/showthr...999#post300999

                                      Inverter testing using old CFL:
                                      http://www.badcaps.net/forum/showthr...er+testing+cfl

                                      Tear down pictures : Hit the ">" Show Albums and stories" on the left side
                                      http://s807.photobucket.com/user/budm/library/

                                      TV Factory reset codes listing:
                                      http://www.badcaps.net/forum/showthread.php?t=24809

                                      Comment


                                        #20
                                        Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                                        Removing connector CN802 and plugging in the power cord turns the BL on and it will stay like that forever. However, I wasn't monitoring the BL-On or DET-5V lines to see if it was doing anything other than staying steady. I'll go do that now.
                                        Howard
                                        Seattle, WA

                                        Comment

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