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

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    #21
    Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

    Ok, now I guess I can move on to heating the main board. When I plugged it in the BL came on and stayed on for the 4-5 minutes that I monitored it. Pins 12 (BL-On) & 14 (DET-5V) stayed steady for the duration. There is one little mystery though - about every 5-7 seconds I would hear a low, but distinct, "tick" sound. It sounded like it was coming from either the main board or in the display above and to the left of the main board. I don't know of any mechanical components so unless its a spark gap arcing over I don't know what else it would be.
    Howard
    Seattle, WA

    Comment


      #22
      Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

      Btw, there's a YT https://www.youtube.com/watch?v=RL5-GtwypiY by user NorCal715 on measuring the voltages for this set and I think he said that 0v on pin 14 (DET-5V) meant no problem which is the opposite of what we're seeing. This one powers/starts up right around 0vdc and then goes to 5vdc for the 28 second duration before the TV cycles. I wouldn't expect it to take 28 seconds for an error on this line to either shut the PS down or at least restart it - should be immediate.
      Last edited by Howard_Woodard; 01-08-2020, 10:06 PM.
      Howard
      Seattle, WA

      Comment


        #23
        Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

        Since you backlights stay on while DE-5V is high when doing the self test then the power supply board is OK, if there is problem with backlights or backlights circuit then it should have gone into protection shutdown when performing self test.
        The link to youtube does not work.
        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


          #24
          Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

          Re-try the link now.
          Howard
          Seattle, WA

          Comment


            #25
            Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

            Ok, the heat gun on the main board had no discernible effect. Unless someone has a better idea for next step, I think it's time to remove the heat sink from the set-top processor (It's a Samsung SEMS13-LF which uses a ball grid array) and try heating it enough with the gun to re-flow the solder joints. Its worth a try and can't hurt.

            Any other ideas?
            Last edited by Howard_Woodard; 01-09-2020, 01:49 PM.
            Howard
            Seattle, WA

            Comment


              #26
              Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

              I tried to reflow the processor's ball grid array -- had some luck in the past with graphics chips -- and at first thought it might have fixed the problem. Even though the set auto-booted, which it shouldn't have, everything else appreared to be working. However, after shutting it off with the remote it began looping again -- not the first time I've seen this.

              As I said in the first post, I see more noise, looking mostly at the 5 vdc rail, than I think I should. Knowing that could cause wierd signals throughout the main board controls I have started looking for the source. I recapped the PSU when I first started with good quality caps with low ESRs so I don't suspect a failed filter cap. I looked at the 8 10 pf tantalum caps on the outputs of the 2 inverter transformers. The signal for each of them, though messy (see attached pic), was the same so it would appear any noise being introduced is being introduced upstream. So my next set of measurements will be around the two switching transistors as well as the DT801S transformer. I'll report back when I get them but in the meantime would appreciate any and all additional help and/or ideas.
              Attached Files
              Last edited by Howard_Woodard; 01-09-2020, 07:48 PM.
              Howard
              Seattle, WA

              Comment


                #27
                Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                This is the waveform at the yellow test point between high voltage MOSFETs QI820 & QI821.

                This waveform looks confused but I don't know what a known-good board would show right here.

                Anybody?

                I guess the next step is to see if there is any difference at the outputs (pins 1 & 5) of transformer DT801S.
                Attached Files
                Last edited by Howard_Woodard; 01-09-2020, 10:00 PM.
                Howard
                Seattle, WA

                Comment


                  #28
                  Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                  Well, being the eternal optimist that I am, I think I may be getting close. The input to the gates of the two mosfets responsible for proving the switching input to the TI801S and TI802S primaries is different. The gate for QI820 is a pulsed square wave (with a few echos) coming from pin 1 of DT801S. However, the gate of QI821 which comes from pin 5 of DT801S, and is probably the same voltage as pin 1, just the opposite polarity in relation to pwr grnd pin 4, is a steady 8 vdc. That narrows things down to 1/2 the windings of transformer DT801S (not likely) to two Shottky diodes (maybe), 5 resistors (not likely) and transistor QI811 (could very well be). These components are on the bottom of the board so I'll need to pull the board and locate the top-side test points for them. I'll do that tomorrow.

                  How'm I doin' so far Bud?
                  Attached Files
                  Howard
                  Seattle, WA

                  Comment


                    #29
                    Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                    I would disable the BL-ON by keeping it grounded, then for the DET-5V it should be either normally high or normally low to satisfy the main board error feedback, then see if the TV still reboot itself or not when the inverter circuit is not running.
                    Last edited by budm; 01-09-2020, 10:28 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


                      #30
                      Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                      Thanks, I’ll try that first thing tomorrow.
                      Howard
                      Seattle, WA

                      Comment


                        #31
                        Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                        Sorry to just now be getting on this but since I've been retired, "first thing tomorrow" has been getting later and later.

                        First I put probes on pins 12 & 14 (inverter on/off and DET_5V) and plugged the TV in. Shortly after the start-up chimes both lines went high (4.9-5.2 vdc) and the backlight came on. The TV looped as previously described -- each time, just before it would restart, both lines would go low.

                        Then, as Bud suggested, I grounded CN802 pin 12 (Inverter On/Off) and left the probes on. When I plugged it in, pin 12 was low (grounded), the backlight did not come on and pin 14 (Det_5V) was low. At the time pin 14 would previously have gone high I could see it "snap" up to about 400mv before quickly coming back down to approx 180mv. The set looped at 28 second intervals just as before.

                        What do you think? Does this point us in any particular direction, or, at least, away from any particular direction(s)?

                        Btw, if you want to see what I mean by the DET_5V line "ticking", I have attached a zipped .mpg file that shows the line being monitored for a complete loop. In it I say "jack" 820 but meant "jumper" 820.
                        Attached Files
                        Last edited by Howard_Woodard; 01-10-2020, 04:38 PM. Reason: Add a zipped video file...
                        Howard
                        Seattle, WA

                        Comment


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

                          Anything <1V is consider logic low, so 400mV still low.
                          What happen if you do not have det_5v line connected back to the main board and still keep the bl-on line low? Will the TV still power cycle itself?
                          You may also have to try pulling the main board DET_5V line high or low and see what happen.
                          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


                            #33
                            Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                            Thanks. I'll fiddle with what the DET_5V signal is telling me and where its coming from tomorrow.
                            Howard
                            Seattle, WA

                            Comment


                              #34
                              Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                              We just trying to simulate the DET-5 error signal to make the main board thinks that there no error signal (because bl-on low) from the inverter circuit.
                              We are just trying to prove that the backlights inverter is not the one that cause the TV to power cycle by disabling the inverter circuit and fool the main board that the inverter circuit is OK.
                              I do not know if the main board wants to see LOW or HIGH signal for normal condition for the DET_5V, that is why you have to simulate LOW by grounding the main board DET_5V pin or pull it high using 1K resistor and stby power supply.
                              Last edited by budm; 01-10-2020, 07:41 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


                                #35
                                Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                                Got it - thanks.

                                Btw, is there any problem disconnecting the PSU from the CCFL sockets and powering it back up?
                                Howard
                                Seattle, WA

                                Comment


                                  #36
                                  Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                                  If the bl-on is present but the CCFL is not connected, the inverter circuit will shutdown after trying to fire up the CCFL, when the CCFL is mot present, the firing Voltage can be as high as 2500 V so I would suggest to always the CCFL connected otherwise you will have arc over.
                                  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


                                    #37
                                    Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                                    Interesting. I think I read that one of the purposes of the DET_5V error line was to shut down the PSU if over-current conditions were detected in the inverter an/or CCFL bulbs. How would you know whether a problem is the inverter or one or more of the bulbs?
                                    Howard
                                    Seattle, WA

                                    Comment


                                      #38
                                      Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                                      Originally posted by Howard_Woodard View Post
                                      Interesting. I think I read that one of the purposes of the DET_5V error line was to shut down the PSU if over-current conditions were detected in the inverter an/or CCFL bulbs. How would you know whether a problem is the inverter or one or more of the bulbs?
                                      1) Det_5V error signal is generated by the backlights inverter circuit when the inverter circuit detect error, it will cause the inverter circuit to go into latched shutdown, it does not shutdown the power supply (the standby power supply, the switched power supply, the PFC Boosted Voltage), it also sends the error signal to the main board, most old TV does not even use this error signal.
                                      2) The inverter has its own protection circuit that detects open lamp, or over current which will latch the inverter circuit into shutdown, it will only take one bad lamp to cause protection shutdown. You power supply/inverter/lamps must be OK otherwise it will not stay on in self test mode (cable not connected to the main board) as long as the AC is present.
                                      3) The standby power supply, the switched power supply, the PFC Boosted do not have have latched shutdown when over current occur, it will go into cycle on/off.
                                      So the key point is that if you disable the inverter circuit and the error feedback but the TV still goes into boot loop, then it is not the inverter issue. As far as the main board is concern, if it is fooled that the DET_5V is OK, but the TV still goes into boot loop then something else is causing the boot loop 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


                                        #39
                                        Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                                        Hi again Bud. I put a 1K pull-up to the 5V rail (pin 2) on the DET_5V line (pin 14). It still loops. On the scope it goes to 5V at about the same time that the BL comes on. Then, at approx 28 seconds, as always, you see a momentary "tick" on the line before it drops to 2.8v (the pull-up value) and then re-boots and continues that regular looping.
                                        Howard
                                        Seattle, WA

                                        Comment


                                          #40
                                          Re: Samsung 32 inch (LN32B360C5D) in perpetual restart loop...

                                          Did you force BL-ON line low and also disconnect the DET-5V wire from the power supply side and force the DET_5V pin on the main board side?
                                          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

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