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    Samsung 710N constant flicker

    Need expert advice once again.

    Been staring at this 710N whose backlight flickers about 10 times per second. Pretty annoying. It seems like setting brightness to 100 sets the duty cycle to 90% or so and at about brightness 20 the monitor just shuts off. It's like the inverter is getting a low PWM signal somewhere, can't figure out where.

    - Tested with different backlight panel -> same issue
    - installed new(ish) caps on the 15V and 5V bus
    - 15V and 5V bus look good. 15V dips to 13V-14V when the CCFLs come on
    - transformers check out - ~950ohm on the secondary
    - inverter fet and transistor check out good

    The only slightly strange thing I could find is the input bus is at 162 where it is normally 169VAC. It can't be that, though?

    The only other thought I have is if it's those square capacitors by the transformers (names escape me right now). I'm too lazy to pull them out to test on my DVM's "CAP" setting... someone tell me if I should?

    ADJ_BL from the logic board is ~0.535VDC. Not sure what it should be.

    I can't find schematics for this inveter board. It is FSP035-2PI01. Other ideas?
    Attached Files

    #2
    Re: Samsung 710N constant flicker

    Pictures are not sharp enough for trouble shooting.
    As you have tested most components I would change the tuning caps you refer to - i dont think you can test them properly with a dvm.
    When you tested the voltages including the Big Cap were the steady or do any vary in time with the flicker? Check any voltage regulators?
    Last edited by selldoor; 08-01-2012, 02:02 AM.
    Please upload pictures using attachment function when ask for help on the repair
    http://www.badcaps.net/forum/showthread.php?t=39740

    Comment


      #3
      Re: Samsung 710N constant flicker

      I forgot to turn macro on. I'll reshoot the photos.

      I didn't see any voltages flicker on the DVM (it has a little bar that sometimes works for low frequency flickers).

      15VDC, 5VDC, 3.3VDC all looked steady except the 15VDC dips to about 14V when the backlight is on.

      I think I'm going to look for the inverter driver spec sheet.

      Comment


        #4
        Re: Samsung 710N constant flicker

        A flickering backlight can be sometimes caused by the large cap failing. Usually for the larger can electrolytics a normal cap test is sufficient.
        Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
        For service manual, schematic, boardview (board view), datasheet, cad - use our search.

        Comment


          #5
          Re: Samsung 710N constant flicker

          Hmm... can't seem to edit my old post to replace the pictures.

          Anyways, I think it was much too late at night in my original post. Here is some updated information:

          - 13V bus does flicker a bit. On my DVM it is 13.10-13.25, but I'm sure it is more than this on a scope.
          - when the backlight is off this bus is up to 15.7-15.8VDC which seems odd.
          - 5V bus is stable.
          - checked the output diodes but there are no shorts

          To do:
          1. There is 2 x 470uF and 1x330uF on the 13V bus. I failed to replace the 1x330uF so will do that, maybe up the total from 1270 to 1500uF or so.
          2. Check that Big Cap
          3. Other circuit tracing since I don't have a schematic...
          Attached Files

          Comment


            #6
            Re: Samsung 710N constant flicker

            The 13V is not tightly regulated, it will go up due to no bog load by the inverter circuits. You can use 470uF in paklce of the 330uF.
            You can check to see if the bg cap is filtering OK or not by setting your True R.M.S meter to AC volt and chek the AC ripple on that main DC filter cap in the primary circuit, it hsould be less than 5% or better of the DC reading.
            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


              #7
              Re: Samsung 710N constant flicker

              Big cap checked out. ripple was about 4VAC or 2.5% of 160VDC.
              Replaced that 330uF cap with 470uF, but the 330uF was still good.

              Officially stumped.
              Any ideas on what VR1 does?
              I dug up someone's schematic and am trying to figure out the BIT3102A circuit which is the CCFL PWM Controller. It seems like this sort of flickering could come from here, especially if it shuts off when i reduce the brightness.

              I appreciate everyone's time on this. I'm sticking with this to learn about these circuits, otherwise I would have trashed this one a long time ago!
              Attached Files

              Comment


                #8
                Re: Samsung 710N constant flicker

                How did you measure ripple?
                Please do not PM me with questions! Questions via PM will not be answered. Post on the forums instead!
                For service manual, schematic, boardview (board view), datasheet, cad - use our search.

                Comment


                  #9
                  Re: Samsung 710N constant flicker

                  Id still think about the tuning caps or even the 4 blue high voltage caps.

                  Is there another board on the back of the panel if the dim/brightness controls are via that
                  are there any voltage regulators or caps on there that could affect it.
                  Please upload pictures using attachment function when ask for help on the repair
                  http://www.badcaps.net/forum/showthread.php?t=39740

                  Comment


                    #10
                    Re: Samsung 710N constant flicker

                    I am thinking about the same tuning caps (C19, 20) for this Royer Oscillator setup.
                    The pot is for adjusting the oscillator (U1.2) frequency that is use for PWM (variable pulse widths is done through the Adj INPUT (Variable DC) and process by the quad op-amp lm324) which drive the U2 (not much info about U2), output of U2 drive the MOSFET U3 which sinks the Emitter current of Q4~7 (Inverter Royer Oscillator circuits), the more U3 conduct, the more power applied to Q4~7, hence more output to drive the lamp.
                    If you short D9/D10 Anode to ground, then you will have max lamps brightness.
                    Most other circuits use the MOSFET for sourcing the current for the Collectors of the Inverter Oscillator.
                    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


                      #11
                      Re: Samsung 710N constant flicker

                      tom66: ripple checked with True RMS DVM on AC across the big cap. I'm not concerned about the supply voltage anymore.

                      - Tuning caps removed and checked out at exactly .15uF per spec. Reinstalled.

                      - Blue HV caps show no shorts, not sure how else to check them?

                      - Also tried to use the inverter board from a 940, but the unit wouldn't turn on.

                      Next thing I'm going to do is try to pull pin4 of U2 low to get max duty cycle out of the PWM controller (I think). If that makes the screen go solid bright, then I know it's either in the logic board signal or in the rest of that PWM generator circuit from U1.1 and U1.2. Hope nothing blows up!

                      budm: If short D9/D10 anodes to gnd, doesn't that also kill the PWM that is driving the xfmr?

                      Also going to start looking for another 710/910...

                      Comment


                        #12
                        Re: Samsung 710N constant flicker

                        Is the Monitor one you were regularly using,when the fault started,OR,is this one that you had not seen before,and was faulty when you switched it on ?????

                        Comment


                          #13
                          Re: Samsung 710N constant flicker

                          Does it flicker with and without source connected - self test mode.
                          Please upload pictures using attachment function when ask for help on the repair
                          http://www.badcaps.net/forum/showthread.php?t=39740

                          Comment


                            #14
                            Re: Samsung 710N constant flicker

                            I'd replace some of the small electrolytic caps in the PSU and go from there.
                            Muh-soggy-knee

                            Comment


                              #15
                              Re: Samsung 710N constant flicker

                              Update:
                              Still poking away at this once in a while. I got another 710N but it had the same issue though the flicker is at a slower rate. Swapped the power boards and the problem sticks with the power boards not the signal. I suspect the BIT3102A output but will have to borrow a scope to figure this out.

                              Comment


                                #16
                                Re: Samsung 710N constant flicker

                                Try the resistor trick with the eeprom chip on the logic board. See here:
                                http://www.monsieurmaggot.com/Samsung.html
                                "We have offered them (the Arabs) a sensible way for so many years. But no, they wanted to fight. Fine! We gave them technology, the latest, the kind even Vietnam didn't have. They had double superiority in tanks and aircraft, triple in artillery, and in air defense and anti-tank weapons they had absolute supremacy. And what? Once again they were beaten. Once again they scrammed [sic]. Once again they screamed for us to come save them. Sadat woke me up in the middle of the night twice over the phone, 'Save me!' He demanded to send Soviet troops, and immediately! No! We are not going to fight for them."

                                -Leonid Brezhnev (On the Yom Kippur War)

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