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LED 27" monitor PSU issue - np power to LED array

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    LED 27" monitor PSU issue - np power to LED array

    Hi all, picked up a faulty Hanns-g HL272HPB free for spares/repair hoping it was just a re-cap...

    I found 1 cap with a bulge and an out of spec reading.

    100uF 100V see pics.

    I've replaced it with a like for like value.

    Not so fast... still no power on

    More testing results next post.

    Dougie
    Attached Files

    #2
    Re: LED 27" monitor PSU issue - np power to LED array

    So time for some readings...

    Heres a pic of the underside, there are 2 test points labelled on the PCB, one for 5Vdc and one for 24Vdc.

    I also read the mains AC (244Vac) and rectified DC at the 2 paralleled 53uF 450v filter caps (336Vdc).

    Took some readings at the other caps too, see pic.

    Dougie.
    Attached Files

    Comment


      #3
      Re: LED 27" monitor PSU issue - np power to LED array

      I checked 2 surface mount TO-262 packages in the 24v test point area of the board, part numbers 050N10 and S20N10, desoldered and checked them in the mini tester. Also tested the gate switch function OK with a DMM. See pic for results.

      Dougie.
      Attached Files

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        #4
        Re: LED 27" monitor PSU issue - np power to LED array

        E19 capacitor ok ?

        Comment


          #5
          Re: LED 27" monitor PSU issue - np power to LED array

          Do you have BLon?

          Comment


            #6
            Re: LED 27" monitor PSU issue - np power to LED array

            Originally posted by diif View Post
            E19 capacitor ok ?
            Looks like a slight bulge on it, took it out and measured in the mini tester. I replaced it with 2 x 47uF 63v in series and got a good spec and ESR.

            The replacement E19 caps read 39v across it.

            Dougie.
            Attached Files

            Comment


              #7
              Re: LED 27" monitor PSU issue - np power to LED array

              Originally posted by CapLeaker View Post
              Do you have BLon?
              No lights to indicate it's on after mains power applied, soft power switch doesn't light up.

              I took some readings from the AV panel driver board, pic attached.

              Dougie
              Attached Files

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                #8
                Re: LED 27" monitor PSU issue - np power to LED array

                Your problem may be in the motherboard, since 5v power is supplied to the board, but there is no command to turn on "EN".
                Check power to DC-DC converters.
                Last edited by lotas; 08-03-2022, 03:42 AM.

                Comment


                  #9
                  Re: LED 27" monitor PSU issue - np power to LED array

                  Originally posted by lotas View Post
                  Your problem may be in the motherboard, since 5v power is supplied to the board, but there is no command to turn on "EN".
                  Check power to DC-DC converters.
                  Here's some shots of the AV/logic board, top and bottom sides.

                  I don't see any obvious issues or where the fault could be on the board.

                  Dougie
                  Attached Files

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                    #10
                    Re: LED 27" monitor PSU issue - np power to LED array

                    What are the voltages relative to earth at these points?
                    Attached Files

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                      #11
                      Re: LED 27" monitor PSU issue - np power to LED array

                      Originally posted by lotas View Post
                      What are the voltages relative to earth at these points?
                      I've attached the photo with the 2 readings.

                      Thanks for your help

                      Dougie.
                      Attached Files

                      Comment


                        #12
                        Re: LED 27" monitor PSU issue - np power to LED array

                        You have a low voltage at the input should be 5v, at the output 3.3v.
                        Attached Files

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                          #13
                          Re: LED 27" monitor PSU issue - np power to LED array

                          Originally posted by lotas View Post
                          You have a low voltage at the input should be 5v, at the output 3.3v.
                          The 5v to 3.3v regulator on my board is a CYT8117T33 and the IC it feeds its output to pin 3 of this package labelled "8912k 245168", can't find any info on the codes.

                          I checked he caps around them and all ok.

                          So 1st I'll order the 5-3.3v regulator and replace it.

                          Dougie
                          Attached Files

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                            #14
                            Re: LED 27" monitor PSU issue - np power to LED array

                            This regulator is the same (1117 33) with a fixed voltage of 3.3v.
                            Attached Files

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                              #15
                              Re: LED 27" monitor PSU issue - np power to LED array

                              8912k - APE8912
                              Attached Files

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                                #16
                                Re: LED 27" monitor PSU issue - np power to LED array

                                Originally posted by lotas View Post
                                8912k - APE8912
                                Thanks, good find!

                                Both regulator IC output readings are low, but the 1.5v reg IC Vin is fed from the 3.3v reg Vout so we can assume the 1.5v reg is OK? It relies on the 3.3v from the other reg IC and Vin has to be 1.5v higher than Vout, its Vin is currently only getting 1.52v.

                                Could a fault in the 1.5v reg IC take out the 3.3v reg IC?

                                So, maybe best to replace both...

                                Dougie.

                                Comment


                                  #17
                                  Re: LED 27" monitor PSU issue - np power to LED array

                                  It is unlikely that 8912k suffered, 3.3v not only power it, you can check by applying 3.3v from a laboratory power supply to this point and check.

                                  Comment


                                    #18
                                    Re: LED 27" monitor PSU issue - np power to LED array

                                    Originally posted by lotas View Post
                                    It is unlikely that 8912k suffered, 3.3v not only power it, you can check by applying 3.3v from a laboratory power supply to this point and check.
                                    Yes, I wouldn't expect these ICs to draw much, datasheet notes 3A typical and 5A max and I wouldn't expect it to need that much.

                                    I applied 5v from the bench supply to pin 3/Vin on the 5-3.3v reg IC and got 3.3v pin2/Vout then tested at pin3/Vout on the 3.3-1.2v reg IC and it read 1.2v so all good there.

                                    The power LED lit up and I was able to power on/off the motherboard via the on/off button. I only connected the front panel button/LED board header and nothing else.

                                    So now to find out what has happened to the 5v supply we have from the PSU board header and the 5v-3.3v reg IC.

                                    Dougie.
                                    Attached Files

                                    Comment


                                      #19
                                      Re: LED 27" monitor PSU issue - np power to LED array

                                      Very strange!
                                      I connected all the headers and the panel flat cable to test the 5v from the PSU header board again, the power led lit up and I cot a check cable message on the LCD panel

                                      I'll put everything back in the casing and test with an HDMI input etc...

                                      Dougie.

                                      Comment


                                        #20
                                        Re: LED 27" monitor PSU issue - np power to LED array

                                        Check the connector and the passage of 5v to 1117 and the capacitors in the power supply on the 5v bus.
                                        Attached Files

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