Lowry GS32FHD in Standby

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  • dick_barton
    Badcaps Legend
    • Aug 2015
    • 6642
    • Wales

    #1

    Lowry GS32FHD in Standby

    Hello All,
    A friend has just dropped off his Lowry GS32FHD TV which he said was stuck in standby.

    Mainboard 17MB35-4 060109
    Power supply 17PW26-4 V.1

    One turning it on it operated perfectly for about 15 minutes with no noticeable problems before switching itself back into standby.
    Using the remote to turn the set back on, after a short delay the backlight flicker on/off and the set immediately returns to standby.

    With the power supply disconnected from the mainboard the standby voltages are present.

    Jumping PS_On to 0V and BL On/Off to +5V using 1K resistors brings on the backlights with no issues.

    Have looked at the data in/out lines of the SPI chip (25L1605D) with an oscilloscope I can see data buzzing on the data in/out lines so I don't believe it to be a failed chip.

    Reconnecting the power supply to the mainboard I have the following voltage when switching on out of standby given as an attachment.

    I suspect it is a power supply fault with the 24V inverter supply being 22.8V and the 12V supply to the board being only 10.9V.
    Voltage at D898 is 329V in standby and 335V out of standby. Schematic says 400V and would explain why the 24V and 12V supplies are slightly lower than they should be.

    Would I be correct in saying this is a PFC circuit problem.

    Does anyone have a better schematic for this model (17PW26-4 V.1) since I find it hard to navigate around.
    Thanks
    Attached Files
    Last edited by dick_barton; 08-04-2016, 09:25 AM.
    Willing to help but I'm no expert.
  • CapLeaker
    Leaking Member
    • Dec 2014
    • 7973
    • Canada

    #2
    Re: Lowry GS32FHD in Standby

    I agree. The 12V/24V rails are off in voltage and the PFC is off (as not turned on). Your are just on plain rectified mains. Check VCC and gate drive on the PFC. Be careful probing around with the oscilloscope in the primary circuit. But I think you know that already.

    I think the PFC may be on the back side of the board (IC802 FAN7529)?
    Never mind I found it.
    Last edited by CapLeaker; 08-04-2016, 10:30 AM.

    Comment

    • dick_barton
      Badcaps Legend
      • Aug 2015
      • 6642
      • Wales

      #3
      Re: Lowry GS32FHD in Standby

      Thanks for the confirmation Capleaker. I'll do a component test around that area to begin with and check for any doggy connections in the light that it initially ran for 10-15mins when first powered up.
      Willing to help but I'm no expert.

      Comment

      • budm
        Badcaps Legend
        • Feb 2010
        • 40746
        • USA

        #4
        Re: Lowry GS32FHD in Standby

        Check PFC Diode D898 (1N5406, next to the Bridge rectifier) for shorts.
        Also check D822, 833 next to PFC Q813.
        Last edited by budm; 08-04-2016, 12:40 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

        • dick_barton
          Badcaps Legend
          • Aug 2015
          • 6642
          • Wales

          #5
          Re: Lowry GS32FHD in Standby

          Thanks Budm,
          Lifted the components out to test D882, D883, Q813 & D898 and all test OK.
          Willing to help but I'm no expert.

          Comment

          • ReeceyBurger123
            Never Give Up !
            • May 2014
            • 7325
            • Britain

            #6
            Re: Lowry GS32FHD in Standby

            Disconnect Psu from mb and apply power with no resistors on anything, you should have 12v,3.3v,5v,24v rails. Had this issue shorted hdmi chip on the mb.
            Please Do Not PM My Page Asking For Help Badcaps Is The Place For Advise, Page Linked For Business Reasons Only. Anyone Doing So Will Be Banned Instantly !

            https://www.facebook.com/Telford-Tel...7894576335359/

            Comment

            • CapLeaker
              Leaking Member
              • Dec 2014
              • 7973
              • Canada

              #7
              Re: Lowry GS32FHD in Standby

              Originally posted by ReeceyBurger123
              Disconnect Psu from mb and apply power with no resistors on anything, you should have 12v,3.3v,5v,24v rails. Had this issue shorted hdmi chip on the mb.
              He already forced it on Reecy...

              Comment

              • CapLeaker
                Leaking Member
                • Dec 2014
                • 7973
                • Canada

                #8
                Re: Lowry GS32FHD in Standby

                pin 5 is PFC_OFF btw so probe that too.

                Comment

                • dick_barton
                  Badcaps Legend
                  • Aug 2015
                  • 6642
                  • Wales

                  #9
                  Re: Lowry GS32FHD in Standby

                  Originally posted by CapLeaker
                  pin 5 is PFC_OFF btw so probe that too.

                  Hello CapLeaker
                  Will do thanks.
                  Shouldn't the PFC voltage remain stable at close to 400V when it fires up?
                  If I look at the 400V rail with my meter set to AC volts I can see the voltage peak up to 390V, drop, 390V, drop or is this the PFC IC switching on and then shutting down, switching on, shutting down.
                  I'll 'scope it in the morning and see what is going on.
                  Thanks
                  Willing to help but I'm no expert.

                  Comment

                  • CapLeaker
                    Leaking Member
                    • Dec 2014
                    • 7973
                    • Canada

                    #10
                    Re: Lowry GS32FHD in Standby

                    if the PFC works correctly, you should have 390V DC on the main filter cap.

                    Comment

                    • dick_barton
                      Badcaps Legend
                      • Aug 2015
                      • 6642
                      • Wales

                      #11
                      Re: Lowry GS32FHD in Standby

                      Originally posted by CapLeaker
                      if the PFC works correctly, you should have 390V DC on the main filter cap.
                      Thanks CapLeaker.
                      I've 'scoped the controller chip and the waveforms are completely up the creek.
                      The supply voltage is fine 14.5V. Waveforms below.

                      I've found a cheap replacement on Ebay and have ordered it. This will allow me to give the TV back and fault find the psu in my own time giving me a spare board.


                      The waveforms were taken with a x200 probe so 1V on the scale = 200V
                      Thanks to all for your help.
                      Attached Files
                      Willing to help but I'm no expert.

                      Comment

                      • dick_barton
                        Badcaps Legend
                        • Aug 2015
                        • 6642
                        • Wales

                        #12
                        Re: Lowry GS32FHD in Standby

                        The replacement power supply has just been fitted and set is now up and running.
                        Willing to help but I'm no expert.

                        Comment

                        • dick_barton
                          Badcaps Legend
                          • Aug 2015
                          • 6642
                          • Wales

                          #13
                          Re: Lowry GS32FHD in Standby

                          Just for information.

                          This was an odd fault. I could force the backlights on without the mainboard connected. I could run the set with the backlights disconnected but obviously sound and no picture but I could not run both.
                          I believe that CapLeaker was correct and it was a failure but not total failure of the PFC circuit.
                          Willing to help but I'm no expert.

                          Comment

                          • vinceroger69
                            Badcaps Legend
                            • Mar 2012
                            • 6714
                            • uk

                            #14
                            Re: Lowry GS32FHD in Standby

                            Thanks for posting the update/fix some boards can be a pain too fix so a board swap is what i usually do too, the old psu with time you maybe able to repair or as always they are usefull for spare parts etc.

                            Comment

                            • dick_barton
                              Badcaps Legend
                              • Aug 2015
                              • 6642
                              • Wales

                              #15
                              Re: Lowry GS32FHD in Standby

                              Hello vinceroger69, Thats my intention to fix it in my own time and have a spare.
                              Willing to help but I'm no expert.

                              Comment

                              • vinceroger69
                                Badcaps Legend
                                • Mar 2012
                                • 6714
                                • uk

                                #16
                                Re: Lowry GS32FHD in Standby

                                Originally posted by dick_barton
                                Hello vinceroger69, Thats my intention to fix it in my own time and have a spare.
                                Yes thats what i try to do too and i can learn from more troubleshooting stages etc and i like the challenge too im sure you will fix this given time.

                                Comment

                                • dick_barton
                                  Badcaps Legend
                                  • Aug 2015
                                  • 6642
                                  • Wales

                                  #17
                                  Re: Lowry GS32FHD in Standby

                                  Final update.

                                  I removed R817, R818, R819 (all in series) due to having odd readings when in place. Off the board they measured correctly at 619K each. Cleaned up the pads on the board and resoldered the resistors back in place and now all the output voltages are correct.
                                  3.35V, 11.97V, 24.7V with no other boards connected

                                  Looks like I may now have a spare board.
                                  Last edited by dick_barton; 08-10-2016, 07:14 AM.
                                  Willing to help but I'm no expert.

                                  Comment

                                  • armoured_smiler
                                    Member
                                    • Sep 2008
                                    • 13
                                    • UK

                                    #18
                                    Re: Lowry GS32FHD in Standby

                                    Hi, Please can you tell me did the resistors still have 'odd' reading when back in place?

                                    "I removed R817, R818, R819 (all in series) due to having odd readings when in place. Off the board they measured correctly at 619K each. Cleaned up the pads on the board and resoldered the resistors back in place"

                                    Comment

                                    • dick_barton
                                      Badcaps Legend
                                      • Aug 2015
                                      • 6642
                                      • Wales

                                      #19
                                      Re: Lowry GS32FHD in Standby

                                      If I recall they do give odd readings when in circuit and it is best to check them out of circuit to confirm their correct values.
                                      Willing to help but I'm no expert.

                                      Comment

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