LG 50PC1 -where is 5v standby derived from?

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  • Cornboats
    Dave
    • Oct 2010
    • 232
    • United Kingdom
    #21
    Re: LG 50PC1 -where is 5v standby derived from?

    I did a meter check on all connectors going on P800 which goes to main board and had varied resistance with earth. I then refitted board to see what voltage was coming back on pin 2 RL-on. Starts with 5 v then drops rapidly to 0v. I'm scratching my head now because I have a psu board that works perfectly-so the main board must be ok. Maybe it's a connection issue. More testing required I think.

    Tom - if I disable opto should I introduce 5v into pin 1 and then short with pin 2 of P800? If this is ok maybe I could bench test the board by putting on a load on vs and va.
    Last edited by Cornboats; 02-16-2015, 07:48 AM.

      Comment

      • tom66
        EVs Rule
        • Apr 2011
        • 32560
        • UK
        #22
        Re: LG 50PC1 -where is 5v standby derived from?

        I just disabled the optos. Makes the audio pop when it turns off.
        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

          • Cornboats
            Dave
            • Oct 2010
            • 232
            • United Kingdom
            #23
            Re: LG 50PC1 -where is 5v standby derived from?

            Just thought I'd update anybody whose been following thread.
            I took resistance readings on all connector pin outs.(using VS ground) With the exception of the grounds all are 1K +. I did notice that the connector grounds vary from 0 to 12ohm.
            I was only getting 1.1v on pin 1 of P880-AC-det. I swopped micro chip U701 for known good one and set powered up with good picture. Ran for 15 mins then dropped out to standby. Refuses to power up again (relays click in and then off) but 5v in still on pin 1, pin3 S5V, pin7 M5 V0n, pin8 S5V.

              Comment

              • Alastair E
                Chief Womble
                • Mar 2013
                • 1963
                • U.K.
                #24
                Re: LG 50PC1 -where is 5v standby derived from?

                Check for shorts on Vs line Y-SUS board.
                TELEFIX

                How PLASMA SCREENS WORK, X-SUS and Y-SUS what they do--
                http://www.irf.com/technical-info/appnotes/an-1088.pdf
                PLEASE DO NOT EMAIL ME PRIVATELY FOR REPAIR ADVICE. QUESTIONS BELONG ON THE FORUM!

                  Comment

                  • Cornboats
                    Dave
                    • Oct 2010
                    • 232
                    • United Kingdom
                    #25
                    Re: LG 50PC1 -where is 5v standby derived from?

                    Thanks for your advice. I will look for shorts but as this is a known working tv and operates perfectly when fitted with a working smps I suspect the problem lies with the faulty smps board.
                    The board ran perfectly last night for 30 minutes and then shut down with a large pop coming throught the speakers. I monitored VS and VA through out this time. VS started at 195.4 and then slowly decreased to 194.5. VA started at 60.2 dropping to 60.
                    I did a hot spot finger test on all the components on shut down but there was nothing obviously hot.

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