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Samsung LE40A676 takes several minutes to start

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    Samsung LE40A676 takes several minutes to start

    Hi,
    I have a Samsung LE40A676 with the same phenomena as these posts:

    https://www.badcaps.net/forum/showthread.php?t=73891
    https://www.badcaps.net/forum/showthread.php?t=45913

    Blinking red LED and several minutes to start up.
    I have checked the PSU board and there's no visibly bad caps. I have also measured all caps on the PSU board an they all seem to be Ok, just to be shure.
    Does any one know if there's a "bad C102" or similar on this main/video board to replace, as the talk about in the linked threads above?
    I can't see any caps that looks bad or anything else that not looks as it should.

    (I'm sorry if you find this post in another thread but I wasn't able to remove my other post)
    Attached Files

    #2
    Re: Samsung LE40A676 takes several minutes to start

    Start with testing the voltages at the connector on the powerboard the one with the cable that goes from powerboard to mainboard on powerboard side, with EVERYTHING hooked up, you measure them with your mutimeter, set meter to 20 vdc then report them, put neg probe on chassis metal ground, pos probe on pin of connector, measure in standby take note, leave probes where they are then power on tv and again take note of voltages, report them here, example pin 1-ps-on-0 volts standby-power on-3.3 volts. This is how we see what voltages you do or don't have.

    Comment


      #3
      Re: Samsung LE40A676 takes several minutes to start

      Hi,
      Thanks for your reply!
      All voltages seem to be Ok
      Pin 1 is 3.69V (Power on)
      Pin 2 is 5.0V
      Pin 3 is 5.11V (should be 5.3V) Ok
      Pin 7,8 is 12.97V (Should be 13V) Ok
      Pin 13-16 is 5.07V (Should be 5V) Ok
      Pin 19, 21, 22 is 12.96 (Should be 13V) Ok
      Other pins are GND on N/C

      The power goes up and down in interval.
      The interval is 15s high (power on) and 5s low (power off). I get the feeling that it tries to start but fails.

      Comment


        #4
        Re: Samsung LE40A676 takes several minutes to start

        Check all the diodes on the powerboard.

        Comment


          #5
          Re: Samsung LE40A676 takes several minutes to start

          Yes, all diods checked and they are all Ok.
          Since all voltages from the PSU board seems to be Ok and the power is shut of from the mainboard, I would guess the problem is on the main board?
          The attached image shows the red power on signal (pin 1) and the yellow is the 13V output (pin 7) from the PSU board.
          Here we can see that the power-signal goes low befor the 13V starts to drop.
          Attached Files

          Comment


            #6
            Re: Samsung LE40A676 takes several minutes to start

            I did not see specified if the backlight lights up. Unplug the power cord between the power supply and the main and see if the backlight up and stay lit.
            On many Samsungs the control for power and backlight is done with "-" (ground) not "+". Power supplay gives a positive voltage to the respective pins for starting but the processor is the one that keeps the pins on the ground.
            Last edited by yokoono; 02-07-2021, 10:02 AM.

            Comment


              #7
              Re: Samsung LE40A676 takes several minutes to start

              If I unplug the power cord to the main, the PSU won't start because it will not get a "start signal" from the main board... (?)
              Anyway, the backlight does not seem to light up. I measured the voltage on, what I think is the backlight cable/connector, and it was zero (during the "try-to-start-up-sequence" with every thing connected).
              On my PSU-image above, it's the light-blue and white cable in the left lower corner of the image, beside the two transformers.

              Comment


                #8
                Re: Samsung LE40A676 takes several minutes to start

                This power supply does not have built in pullup resistors like other Samsung power supplies.
                This power supply requires +5.3v standby connected to Power on/off to turn ON the power supply (it has a built in 4.7k series resistor RM837) to protect QM807 (on/off transistor)
                To turn on the backlights you need to supply +5.3V standby to pin 1 of CNl803 (inverter On/Off) (has built in 1k RI801 series res.)
                Both CNI803 and CN801 cables need to be disconnected to protect the main board.
                Last edited by R_J; 02-07-2021, 11:58 AM.

                Comment


                  #9
                  Re: Samsung LE40A676 takes several minutes to start

                  Ok, but haven't we already found that the backlight doesn't work/light up?
                  When the PSU starts for 15s, there is no power on the backlight connector witch I guess it should have?
                  Or is the backlight power controlled separately?
                  (I guess the image shows the backlight cable/connector, right?)
                  Attached Files
                  Last edited by Chrille; 02-07-2021, 12:53 PM.

                  Comment


                    #10
                    Re: Samsung LE40A676 takes several minutes to start

                    The voltage on THAT connector is likely around 3~5KV at 60khz, what are you using to try and measure it? That connector feeds a distribution board and the ccfl's, If there is a problem ie: bad connection, bad transformer, bad ccfl etc. the backlight will detect the error and will shut down.
                    Last edited by R_J; 02-07-2021, 01:32 PM.

                    Comment


                      #11
                      Re: Samsung LE40A676 takes several minutes to start

                      I guess I should get something here if it's 3~5KV 60khz but the frequency might be too high...?
                      (I had to zip the movie to be able to attach it)
                      Attached Files

                      Comment


                        #12
                        Re: Samsung LE40A676 takes several minutes to start

                        Originally posted by Chrille View Post
                        I guess I should get something here if it's 3~5KV 60khz but the frequency might be too high...?
                        (I had to zip the movie to be able to attach it)
                        You can't use that to work on electronics, it is for detecting line voltage. You need a dvm or multimeter.

                        Comment


                          #13
                          Re: Samsung LE40A676 takes several minutes to start

                          I have that as well but it can't measure 3~5KV (See previous results)

                          Comment


                            #14
                            Re: Samsung LE40A676 takes several minutes to start

                            Slightly unplug the connector going to the HV distribution board (leave the plug in the connector but allow about 1/8" of distance between the contacts) and see if you get some arcing when first turned on. That will tell you if the high voltage section on the power supply is working
                            I would also remove the black shield from the inverter dis. board and inspect the connections and transformers for each ccfl. You can leave the plastic off but reinstall the ground screws.
                            Last edited by R_J; 02-07-2021, 03:52 PM.

                            Comment


                              #15
                              Re: Samsung LE40A676 takes several minutes to start

                              Since there should be 3-5KV in that cable, I don't want to fiddle too much with that connectors when the PSU is on.
                              Any way, I'm pretty shure that there is no power in these cables because:

                              1. There is no working backlight when the PSU is active.
                              2. I think my electric field detector should detect it.
                              3. All heatsinks gets a higher temperature when the PSU has been powered on for a while but the one with the high-voltage MOSFET-drivers! (STP9NK50ZFP) This one is "cold as ice"

                              My question is: Should the backlight power be active when the PSU is on?
                              If so, there is something with the backlight power!

                              Comment


                                #16
                                Re: Samsung LE40A676 takes several minutes to start

                                Have you checked the 2nd fuse soldered on the board
                                What voltage do you have on pin 1 (Inverter On/Off) of CNI803 and on the remaining pins of that connector?
                                Last edited by dick_barton; 02-08-2021, 01:16 PM.
                                Willing to help but I'm no expert.

                                Comment


                                  #17
                                  Re: Samsung LE40A676 takes several minutes to start

                                  Yes, I've chacked all fuses and they're Ok.
                                  The voltage on the inverter is 31.7 mV when the board is On/active and 3.4 mV when it's in inactive state.

                                  (I've measured the two STP9NK50ZFP and they also seem to be Ok)

                                  Note: This is when the TV is in the not-working-state, i.e. when it tries to power up but fails.

                                  If I let the TV be on for, say 30+ minutes, it sudden comes to a state when it works. In that state, the inverter voltage is 4.91V.
                                  In this state, everything works fine. The backlight is Ok. My electric-field-measure-tool (se video) indicates power in the high-voltage cables.
                                  It's just that, that I don't really like waiting 30 minutes or more to power up the TV! Even when I was a little kid, I didn't have to wait that long!

                                  So here's a small summary:
                                  1. Power coord is unplugged.
                                  2. I plug in the power coord to the wall and power on the TV.
                                  3. The TV tries to start for 30+ minutes but fails.
                                  4. During this time, the inverter signal goes between 3.4mV and 32mV
                                  5. After 30+ minutes, the TV suddenly starts to work.
                                  6. The inverter signal goes to from 32mV to 4.9V at the same time the backlight lights up. (a few seconds efter the PSU has started)
                                  7. I can now power on and off the TV without any problems. I starts directly!

                                  I think it's when it have been shut of a little longer the problem occur...
                                  Last edited by Chrille; 02-08-2021, 03:44 PM.

                                  Comment


                                    #18
                                    Re: Samsung LE40A676 takes several minutes to start

                                    The inverter on/off signal comes from the main board so you could force the power supply on to prove the fault is on the main board
                                    Try using a heat gun to heat areas of the main board to see if it will turn on sooner.
                                    Last edited by R_J; 02-08-2021, 04:30 PM.

                                    Comment


                                      #19
                                      Re: Samsung LE40A676 takes several minutes to start

                                      As RJ says there appears to be an issue with Inverter On signal from the mainboard to the power supply.
                                      Willing to help but I'm no expert.

                                      Comment


                                        #20
                                        Re: Samsung LE40A676 takes several minutes to start

                                        Hey, this is not the way to diagnose... first check the PSU itself by putting the right resistances on the 5,3v and 13v as dummy load, for 5,3v example a 3,3ohm 10w, for 13v 3x3,3ohm 5-10W in series, a diode (not resistor) from A5,3V to Poweron(cathode), and a jumper from poweron to BL_ON. IF the resistors warms up and tensions stays ok the PSU is OK. IF PSU seats down then you need a new PSU (i have one of this model)..
                                        Last edited by Davi.p; 02-08-2021, 06:04 PM.

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