LG 50PQ6000 unstable 5v standby

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  • tom66
    EVs Rule
    • Apr 2011
    • 32560
    • UK

    #201
    Re: LG 50PQ6000 unstable 5v standby

    They would work. Put one across the 4.45V output. Does it stay at 4.45V?
    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

    • Baileybum1234
      Badcaps Veteran
      • Sep 2012
      • 245
      • UK

      #202
      Re: LG 50PQ6000 unstable 5v standby

      Originally posted by tom66
      They would work. Put one across the 4.45V output. Does it stay at 4.45V?
      Drops to 3.9v with the 10 ohm load on the standby 5v line.
      Repaired: LG50PQ6000

      Comment

      • tom66
        EVs Rule
        • Apr 2011
        • 32560
        • UK

        #203
        Re: LG 50PQ6000 unstable 5v standby

        How do two in series (20 ohm) make it drop by?
        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

        • Baileybum1234
          Badcaps Veteran
          • Sep 2012
          • 245
          • UK

          #204
          Re: LG 50PQ6000 unstable 5v standby

          Back up to 4.45V
          Repaired: LG50PQ6000

          Comment

          • tom66
            EVs Rule
            • Apr 2011
            • 32560
            • UK

            #205
            Re: LG 50PQ6000 unstable 5v standby

            Hmm, so maybe that is normal, it might not be designed to support 445mA load. It's probably not bad caps, if it does that. So I really don't know any more. I am out of ideas. I am of course assuming your DMM is correct. Have you checked it against a known good voltage source?
            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

            • Baileybum1234
              Badcaps Veteran
              • Sep 2012
              • 245
              • UK

              #206
              Re: LG 50PQ6000 unstable 5v standby

              DVM is fine. I have 2.

              I have tried using an old computer power supply and injecting 5v to see if anything got hot and that voltage dropped too and made me wounder.

              Looking in the training manual everything says 5v not 4.45v hummmmm

              I hear the relays click and parts of the TV fire for a second then off. Something is up in there somewhere.
              Repaired: LG50PQ6000

              Comment

              • tom66
                EVs Rule
                • Apr 2011
                • 32560
                • UK

                #207
                Re: LG 50PQ6000 unstable 5v standby

                Wait, so when you fed 5V from computer PSU into output of plasma PSU, it dropped??
                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

                • Baileybum1234
                  Badcaps Veteran
                  • Sep 2012
                  • 245
                  • UK

                  #208
                  Re: LG 50PQ6000 unstable 5v standby

                  yes. Made me think some thing was deadish.
                  Repaired: LG50PQ6000

                  Comment

                  • Baileybum1234
                    Badcaps Veteran
                    • Sep 2012
                    • 245
                    • UK

                    #209
                    Re: LG 50PQ6000 unstable 5v standby

                    something is creating an ubnormal load?
                    Repaired: LG50PQ6000

                    Comment

                    • tom66
                      EVs Rule
                      • Apr 2011
                      • 32560
                      • UK

                      #210
                      Re: LG 50PQ6000 unstable 5v standby

                      But I do not understand how a computer PSU which is completely different would drop down to the same voltage.
                      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

                      • Baileybum1234
                        Badcaps Veteran
                        • Sep 2012
                        • 245
                        • UK

                        #211
                        Re: LG 50PQ6000 unstable 5v standby

                        Im not even sure if it was a propper test in all honesty.

                        I was still working on the theory that my 5v standby was low. If I have a good 5v standby voltage to start with I would be prepared to move on with different tests and look elsewhere.

                        I thought I would use one of the 5VDC lines on the computer PSU and just attach it to the standby 5v line to see if it brought the voltage up or maybe caused some heat somewhere for a clue. If I had a test bench power supply I would of tried that. The computer PSU was dragged down I need to retest for the exact results. Maybe there is some mileage in it.
                        Repaired: LG50PQ6000

                        Comment

                        • tom66
                          EVs Rule
                          • Apr 2011
                          • 32560
                          • UK

                          #212
                          Re: LG 50PQ6000 unstable 5v standby

                          I would consider that idea, but the fact that you've got 4.45V under no load tells me something else is wrong with the PSU.
                          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

                          • Baileybum1234
                            Badcaps Veteran
                            • Sep 2012
                            • 245
                            • UK

                            #213
                            Re: LG 50PQ6000 unstable 5v standby

                            Yeah agreed.

                            So I need to trace the 4.45V back and find out where its developed from.
                            Repaired: LG50PQ6000

                            Comment

                            • Baileybum1234
                              Badcaps Veteran
                              • Sep 2012
                              • 245
                              • UK

                              #214
                              Re: LG 50PQ6000 unstable 5v standby

                              Ok IC301 could be something to do with it. Its a str w6252 9531p ssome kind of protection device if it was playing up it would effect the standby 5v.

                              Also need to work out what tappings on the coil I need to look at and the 3 components strapped to the heat sink what they should measure.

                              Its hard to see how exactly the 5v standby is made by following the tracks. Does any one have a simular circuit diagram or have they done it before?

                              Circled in blue.

                              Attached Files
                              Repaired: LG50PQ6000

                              Comment

                              • Baileybum1234
                                Badcaps Veteran
                                • Sep 2012
                                • 245
                                • UK

                                #215
                                Re: LG 50PQ6000 unstable 5v standby

                                Not given up on this im just building up the insperation for another session.
                                Repaired: LG50PQ6000

                                Comment

                                • Baileybum1234
                                  Badcaps Veteran
                                  • Sep 2012
                                  • 245
                                  • UK

                                  #216
                                  Re: LG 50PQ6000 unstable 5v standby

                                  Does any one know of a link that talks through the path and demonstrates how the standby 5v is made?

                                  I have tried to follow the tracks back but they just dissapear.

                                  I feel if I could wok out how the sb5v is produced I could start looking at the components inline and testing them.

                                  Hopefully then working out why I have a low 5vSB might hold a clue. Also maybe I could follow the path and lift a leg on a component to see if the voltage goes upto 5v again indecating a short?
                                  Repaired: LG50PQ6000

                                  Comment

                                  • tom66
                                    EVs Rule
                                    • Apr 2011
                                    • 32560
                                    • UK

                                    #217
                                    Re: LG 50PQ6000 unstable 5v standby

                                    It just comes from the transformer, goes through a diode, into a capacitor.
                                    There's a feedback loop to regulate it too.
                                    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

                                    • Baileybum1234
                                      Badcaps Veteran
                                      • Sep 2012
                                      • 245
                                      • UK

                                      #218
                                      Re: LG 50PQ6000 unstable 5v standby

                                      AC Voltage is supplied to the SMPS Board at Connector SC101 from the AC Input assembly. Standby 5V is developed from 160V source supply (which during run measures 380V measured fromthe primary fuse F302).

                                      This supply is also used to generate all other voltages on the SMPS. The STBY5V (standby) is B+ for the Controller (IC701) on the SMPS and output at P813 pins 11 and 23 then sent to the Main board for Microprocessor (IC1) operation.

                                      So it looks like a good place to start. I should measure 160V across F302 in standby and 380v in run.

                                      Please could I just confirm im measuring across the fuse and not to ground and is it DC or AC at this point. Im in two minds about the second point so would like a second opintion.



                                      Thanks

                                      Jarrett
                                      Attached Files
                                      Repaired: LG50PQ6000

                                      Comment

                                      • tom66
                                        EVs Rule
                                        • Apr 2011
                                        • 32560
                                        • UK

                                        #219
                                        Re: LG 50PQ6000 unstable 5v standby

                                        Your ground ref on the primary is the negative lead of the large caps. Measuring a substantial voltage across a fuse is never good. It indicates the fuse is blown.
                                        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

                                        • Baileybum1234
                                          Badcaps Veteran
                                          • Sep 2012
                                          • 245
                                          • UK

                                          #220
                                          Re: LG 50PQ6000 unstable 5v standby

                                          Originally posted by tom66
                                          Your ground ref on the primary is the negative lead of the large caps. Measuring a substantial voltage across a fuse is never good. It indicates the fuse is blown.
                                          Got you! Cheers.
                                          Repaired: LG50PQ6000

                                          Comment

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