Sylvania LC420SS8 Power Supply Troubleshooting

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  • gravitronic
    New Member
    • Aug 2013
    • 3
    • Canada
    #1

    Sylvania LC420SS8 Power Supply Troubleshooting

    Hi Badcappers!

    I've got this LCD TV in my garage from a friend. It stopped working and has no signs of life. I found this forum via a google search for the service manual for this model, which is in this thread:

    https://www.badcaps.net/forum/showthread.php?t=24445

    I can fix digital electronics relatively easily but this is the first power supply I've tackled, so I'm looking for help.

    The TV shows no signs of life, but no capacitors appear bad from visual inspection.

    Some voltages during standby:
    'ALL 3.3v/5v' at J107: 3.29
    KEY1: 3.26
    KEY2: 0
    'for 5v' at J142: 6.57
    PROTECT2: 0.9
    PROTECT1: 0.09

    None of those voltages change when I press the 'power' button.

    Can anyone help? Thanks!
    Last edited by gravitronic; 08-13-2013, 05:53 PM.
    Tags: None
    • gravitronic
      New Member
      • Aug 2013
      • 3
      • Canada
      #2
      Re: Sylvania LC420SS8 Power Supply Troubleshooting

      Just read enough of the service manual to realize all my debugging of the power board while disconnected from the digital board is totally invalid. Will reconnect those tomorrow and debug from scratch

        Comment

        • aasnowskate
          Senior Member
          • Jan 2013
          • 118
          • usa
          #3
          Re: Sylvania LC420SS8 Power Supply Troubleshooting

          I have the same model TV with the same problem. Please post your findings.
          Thanks in advance.

            Comment

            • brnrubbr
              Member
              • Jun 2013
              • 37
              • United States
              #4
              Re: Sylvania LC420SS8 Power Supply Troubleshooting

              Have you guys had any luck? I just got a no-power LC420SS8. I have got the Backlights working, but the TV eventually shuts off.

              Status: Backlights on, "Digital Television" text, regular flashing green ON light, then a very quick flashing green light and TV turns off.

              I suspect power supply and will troubleshoot tomorrow.

                Comment

                • brnrubbr
                  Member
                  • Jun 2013
                  • 37
                  • United States
                  #5
                  Re: Sylvania LC420SS8 Power Supply Troubleshooting

                  Main board was the cause for my TV. Not too expensive, but I could not find exact circuit cause.

                    Comment

                    • zvaniel4o
                      Member
                      • Feb 2014
                      • 12
                      • US
                      #6
                      Re: Sylvania LC420SS8 Power Supply Troubleshooting

                      Originally posted by gravitronic
                      Just read enough of the service manual to realize all my debugging of the power board while disconnected from the digital board is totally invalid. Will reconnect those tomorrow and debug from scratch
                      Was there any success after you did that?

                        Comment

                        • zvaniel4o
                          Member
                          • Feb 2014
                          • 12
                          • US
                          #7
                          Re: Sylvania LC420SS8 Power Supply Troubleshooting

                          It was not the main board with mine... it was faulty smt and tht diodes... replaced - works like charm!

                            Comment

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