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LG 1918s No power

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    #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
    #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

      #3
      Re: LG 1918s No power

      Originally posted by ethernet View Post
      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

        #4
        Re: LG 1918s No power

        How did you test the bridge rectifier ?

        And have you checked the thermistor ?

        Comment

          #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

            #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

              #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

                #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

                  #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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