LG 1918s No power

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  • ethernet
    Member
    • May 2009
    • 11
    #1

    LG 1918s No power

    Hello,

    Sympoms are:

    No power on
    Transformer clicking

    Diagnosys and Tests:

    No 5V VSB
    No voltage on large cap 100uf 450V
    Bridge rectifier OK
    Mains fuse OK
    0.47uf capacitor OK
    ALL caps look OK but not replaced

    My main concern is why is there NO voltage on large cap?? Can somebody please shed some more light on this case?

    Thank you
    Tags: None
    • sam_sam_sam
      Badcaps Legend
      • Jul 2011
      • 6024
      • USA
      #2
      Re: LG 1918s No power

      Can you post some photo of you control and power board
      and see if can find what up withe monitor

        Comment

        • PlainBill
          Badcaps Legend
          • Feb 2009
          • 7034
          • USA
          #3
          Re: LG 1918s No power

          Originally posted by ethernet
          Hello,

          Sympoms are:

          No power on
          Transformer clicking

          Diagnosys and Tests:

          No 5V VSB
          No voltage on large cap 100uf 450V
          Bridge rectifier OK
          Mains fuse OK
          0.47uf capacitor OK
          ALL caps look OK but not replaced

          My main concern is why is there NO voltage on large cap?? Can somebody please shed some more light on this case?

          Thank you
          That would sound like a tester error. Agree with 3sam, pictures would be a major help.

          PlainBill
          For a number of reasons, both health and personal, I will no longer be active on this board. Any PMs asking for assistance will be ignored.

          Never be afraid to try something new. Remember, amateurs built the ark. Professionals built the Titanic.

            Comment

            • sabre504
              Badcaps Veteran
              • May 2010
              • 449
              • United Kingdom
              #4
              Re: LG 1918s No power

              How did you test the bridge rectifier ?

              And have you checked the thermistor ?

                Comment

                • jetadm123
                  Badcaps Legend
                  • Feb 2010
                  • 2169
                  #5
                  Re: LG 1918s No power

                  If you have zero volts across the main capacitor, then how can you have a "clicking sound"? Suggest you remeasure the voltage across the main cap. Black probe on negative cap lead and red probe on positive cap lead. Be careful as this is high voltage, approx 165 VDC if you're in the USA.

                    Comment

                    • ethernet
                      Member
                      • May 2009
                      • 11
                      #6
                      Re: LG 1918s No power

                      Thank you for the replies,

                      We have 230AC here so i set the dmm to 750V AC and messured the leads on the large capacitor. No volts.

                      I thought it was the transformer clicking but i could be wrong, sound is coming from that area. I will post pictures tomorrow when i am able to access the monitor.

                      Diode checked the bridge rectifier - no shorts and no reverse current flow

                      Thermistor looks ok but i forgot to test it. That would explain the problem i think.

                      Thank you for the answers, i will reply back tomorrow

                        Comment

                        • jetadm123
                          Badcaps Legend
                          • Feb 2010
                          • 2169
                          #7
                          Re: LG 1918s No power

                          The voltage across the main cap is DC, not AC. You should see approx. 230x1.4 = 322 VDC

                            Comment

                            • sabre504
                              Badcaps Veteran
                              • May 2010
                              • 449
                              • United Kingdom
                              #8
                              Re: LG 1918s No power

                              If your large cap is showing voltage and there is clicking coming from the board then the thermistor should be ok .
                              Pictures as stated will help others maybe spot something else that needs testing and can better guide you

                                Comment

                                • ethernet
                                  Member
                                  • May 2009
                                  • 11
                                  #9
                                  Re: LG 1918s No power

                                  Oops i was measuring AC on the large cap.

                                  Large cap has DC Voltage 345V, ALL caps have been replaced except those two small starter caps. Yes i am aware of the irony that the monitor won't start and i have not replaced the starter caps. They are not currently on stock and will replace them when they are available.

                                  Here are the pictures:
                                  Attached Files

                                    Comment

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