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B109-901 Tv Power supply no standby voltage - TCL 40C35F

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    #1

    B109-901 Tv Power supply no standby voltage - TCL 40C35F

    Hi, I've got a B109-901 power supply that is absolutely dead, it has no standby voltage and the main bridge rectifier (highlighted in red) has no ac input voltage, after prodding around for a bit I found a relay that is responsible for delivering mains voltage to the rectifier (highlighted in blue) which for some reason isn't closing when I power the board on, I tested the relay and confirmed that it is good however it seems to have no voltage on it's coil. I followed the traces on the PCB and one of the pins of the relay's coil seems to connect to the rectifiers DC - output while the other goes onto a very complicated array of surface mount components, any ideas on what purpose a relay like this serves? why would you want to disconnect the rectifier from mains?
    Attached Files
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    #2
    Re: B109-901 Tv Power supply no standby voltage

    Whats the TV brand ,and model number .
    All donations to badcaps are welcome, click on this link to donate. Thanks to all supporters

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      #3
      Re: B109-901 Tv Power supply no standby voltage

      It's a TCL tv model number 40C35F

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        #4
        Re: B109-901 Tv Power supply no standby voltage

        The standby ic is likely the 8 pin ic (U401) near the smaller transformer, I suspect there is a low value resistor that feeds it that is open. The picture is too small to make out the model number of the board but it looks like a dafron 4h.B1090.701
        post the number on the ic and we can look up the datasheet for the pinout.
        I suspect D204 & D205 & CE203 are the dc supply source for the standby ic, so check the voltage across CE203.
        Last edited by R_J; 08-05-2021, 09:32 PM.

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          #5
          Re: B109-901 Tv Power supply no standby voltage

          I really appreciate the reply, I've attached some more detailed photos below of the board model number and the IC. The IC is a 7 pin ST VIPER17L, one of the pins is missing however this is intended as there is no hole on the PCB for it. I've measured the voltage across cap CE203 and there is a steady 100v DC. There are 4 more IC's on the bottom of the PCB (images below) 2 on the cold side and 2 more on the hot side. I've also attached the datasheet for the PSU below, it's not for the exact model that I have but the component names seem to match, here are the IC names relative to the images below:

          these might be wrong as it is really hard to read them!

          1 (U701). 324
          ST p777951

          2 (U600). 0Z9972GN
          A93YRL.1G
          0924AT

          3 (U301). EA1530A
          SD9C103
          Hn69452

          4 (U201). L6562A << this one was very hard to read, 2A might be wrong
          ST EZ -- (unreadable)
          Attached Files
          Last edited by Gjackson; 08-06-2021, 07:16 AM.

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            #6
            Re: B109-901 Tv Power supply no standby voltage

            Oops forgot to add photos
            Attached Files

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              #7
              Re: B109-901 Tv Power supply no standby voltage - TCL 40C35F

              Update:

              I searched around a bunch of resistors both smd and through hole
              I found 2 resistors (R425 and R307) that have values that are off,

              R425 should be 180kohm and is 122kohm
              R307 should be 100kohm and is 87kohm

              can this cause issues?

              Thanks.
              Attached Files

              Comment

                #8
                Re: B109-901 Tv Power supply no standby voltage - TCL 40C35F

                The smd ic's on the back (pimary side) are for pfc and the main power supply driver, you need the standby voltage first. Using the negative of the bridge rectifier, check the voltage on pin2 of U401 (VDD) Voltage across CE405, If this cap is bad the ic may not start.

                The schematic is different and does not use the viper17l ic.
                Post a picture of the trace side of U401 so I can trace the circuit.
                Last edited by R_J; 08-06-2021, 11:08 AM.

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                  #9
                  Re: B109-901 Tv Power supply no standby voltage - TCL 40C35F

                  Ok so I measured 6v DC on VDD of U401 and 6v DC across cap CE405, If you want I can take the cap out and see if it has the correct capacitance value.

                  Thanks.
                  Attached Files
                  Last edited by Gjackson; 08-06-2021, 12:14 PM. Reason: Rotated images

                  Comment

                    #10
                    Originally posted by Gjackson View Post
                    Re: B109-901 Tv Power supply no standby voltage - TCL 40C35F

                    Ok so I measured 6v DC on VDD of U401 and 6v DC across cap CE405, If you want I can take the cap out and see if it has the correct capacitance value.

                    Thanks.
                    Conseguiu resolver o problema dessa placa , estou com o mesmo sintoma

                    Comment

                      #11
                      Originally posted by Gjackson View Post
                      Re: B109-901 Tv Power supply no standby voltage - TCL 40C35F

                      Ok so I measured 6v DC on VDD of U401 and 6v DC across cap CE405, If you want I can take the cap out and see if it has the correct capacitance value.

                      Thanks.
                      Conseguiu resolver o problema colega ??

                      Comment

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