LG L1718S no power

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  • llphat
    Member
    • Dec 2010
    • 20
    #1

    LG L1718S no power

    Hello All,

    I have a LG L1718S LCD which does not appear to power up. After taking the monitor apart and inspecting the power supply board, I could not see any bad caps or other bad components.

    I have found the service manual and followed some of the troubleshooting routes for no power on page 15.

    1. Primary rectifier voltage is present, approx 300V at the bridge
    2. Pin3 of IC802 approx 1V present, pin2 abt 2V and pin1 abt 6V all taken against ground of C805 capacitor.

    Service manual doesn't go on from there.

    There is no Vcc5V going out from the power supply board into the controller board.

    Any help would be appreciated. Thanks in advance.
    Tags: None
    • retiredcaps
      Badcaps Legend
      • Apr 2010
      • 9271
      #2
      Re: LG L1718S no power

      Originally posted by llphat
      I have found the service manual and followed some of the troubleshooting routes for no power on page 15.

      1. Primary rectifier voltage is present, approx 300V at the bridge
      2. Pin3 of IC802 approx 1V present, pin2 abt 2V and pin1 abt 6V all taken against ground of C805 capacitor.
      Same comment about pictures. See your other thread.

      If you found the service manual, provide a link so it saves us from searching for it. In addition, manufacturers sometimes use completely different boards, but with the same model number. Thus, we could be looking at completely different service manuals.

      1) What part of the world do you live in?
      2) If you measure the voltage across the main filter capacitor (the biggest one), what is the DC voltage? Careful, with measuring this HIGH VOLTAGE.
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        Comment

        • llphat
          Member
          • Dec 2010
          • 20
          #3
          Re: LG L1718S no power

          Many thanks for your prompt reply.

          I have found the service manuals at below, both look similar:



          As for myself, I'm residing in the U.K.

          I have previously measured the voltage across the main filter capacitor to ensure the primary rectifier is working, the voltage is around 300V. I only have a very cheap multimeter so can't get precise values.

          I have enclosed an image of the power supply board.
          Attached Files

            Comment

            • retiredcaps
              Badcaps Legend
              • Apr 2010
              • 9271
              #4
              Re: LG L1718S no power

              Originally posted by llphat
              As for myself, I'm residing in the U.K.
              1) 300V DC / 1.414 implies 212V AC. That seems correct for the U.K.

              2) Can we also get a picture of the back of the power board?

              3) Assuming IC802 is the PWM, what is the part number for it?
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              We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

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                Comment

                • llphat
                  Member
                  • Dec 2010
                  • 20
                  #5
                  Re: LG L1718S no power

                  Image of the back of the power supply board attached.

                  IC802 is TOP245YN.

                  Thanks for your kind assistance.
                  Attached Files

                    Comment

                    • Rtech
                      Badcaps Legend
                      • Jul 2010
                      • 1095
                      #6
                      Re: LG L1718S no power

                      AC mains in the Uk is 240v, so 300v seems a little low,as the main smoothing cap is across the Bridge,and would expect 330v at least,but as you state the meter you are using is not the greatest, then its possible you can end up running around in circles!!

                        Comment

                        • retiredcaps
                          Badcaps Legend
                          • Apr 2010
                          • 9271
                          #7
                          Re: LG L1718S no power

                          Originally posted by Rtech
                          AC mains in the Uk is 240v, so 300v seems a little low,as the main smoothing cap is across the Bridge,and would expect 330v at least,but as you state the meter you are using is not the greatest, then its possible you can end up running around in circles!!
                          Thanks for the correction. I wasn't 100% sure about voltage there.

                          We have had a number of posters in the last week with weak batteries in the multimeter giving incorrect/inconsistent readings. The OP might want to put in fresh batteries and retest.
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                            • retiredcaps
                              Badcaps Legend
                              • Apr 2010
                              • 9271
                              #8
                              Re: LG L1718S no power

                              There are 2 small caps next to the SPW-047 transformer. Measure and report the voltage across those 2 caps.
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                                Comment

                                • llphat
                                  Member
                                  • Dec 2010
                                  • 20
                                  #9
                                  Re: LG L1718S no power

                                  Thanks for the replies.

                                  When I measure the AC input on my cheap analog meter, I only get around 200V AC. Switch it over to 500V DC range to measure the voltage across the primary filter capacitor I get around 300V.

                                  For the two capacitors near the transformer, one reads around 4V across it and another about 4.5V across it.

                                    Comment

                                    • retiredcaps
                                      Badcaps Legend
                                      • Apr 2010
                                      • 9271
                                      #10
                                      Re: LG L1718S no power

                                      Originally posted by llphat
                                      When I measure the AC input on my cheap analog meter, I only get around 200V AC. Switch it over to 500V DC range to measure the voltage across the primary filter capacitor I get around 300V.
                                      There have been a handful of people lately with bad/weak batteries in their multimeter. Try a fresh new battery in your multimeter and remeasure your AC input and DC voltage across the main filter capacitor.

                                      If you still don't get close to 240V AC, then see if there is calibrate function on your analog multimeter.
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                                      We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

                                      Please do not post inline and offsite as they slow down the loading of pages.

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