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715G3812-P02-H20-003D Philips TV power supply

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    715G3812-P02-H20-003D Philips TV power supply

    Dear everyone,
    I am asking for help to repair this board, as I were not able to solve it on my own.
    Symptom: it has 5V standby, but if I connect the PS-ON pin to high level, the PFC tries to start for a brief moment, but the highest it goes is around 360VDC. If I put it back into the TV and start it with the mainboard, this brief moment extends to about 0.7 second. But it makes the same issue. In the past, the tv was working, altough the voltage on the main filter cap seemed low (around 380V, datasheet suggests 395V)
    So far I have done this:
    Check all diodes
    Check all resistors
    Recap the whole board with quality caps
    Changed the 3 smps ICs: IC901, IC902, IC905
    IC905 makes the 5V standby, as I said, it worked before, but I decided to change it also.
    Changed Q902 PFC FET to a new one
    Nothing helped from the above list. What I noticed, the VDD-S line is 5.8VDC in standby, and it goes higher to about 12-13VDC when I try to start the board, but only for a fraction of a second, then it falls back to 5.8V. I was only able to see it via scope. This 5.8V on the hot side is produced by PIN2 of IC905. From here on, I am clueless. Please see the attached SM, it is on page 44 (power 42" & 47"). There are components marked _NC, they are for the 47" version, are left out on my board.

    Thank you
    Attached Files
    Cheers, Janos

    #2
    Re: 715G3812-P02-H20-003D Philips TV power supply

    The VDD-S voltage comes from T902 via D904, in standby B+ is lower so when pfc starts it might jump up but I don't think it should rise too much
    Do you ever get any +12 volts or +24volts?

    Comment


      #3
      Re: 715G3812-P02-H20-003D Philips TV power supply

      Originally posted by R_J View Post
      The VDD-S voltage comes from T902 via D904, in standby B+ is lower so when pfc starts it might jump up but I don't think it should rise too much
      Do you ever get any +12 volts or +24volts?
      Thank you very much for coming in.
      I have 12V & 24V on the cold side for a brief second, when the board is in the TV. When it is on the workbench, it gives nothing out, even for a milisecond. VDD-S should be around 12-13V, because the 3 SMPS chips have an under-voltage lockout for their power supply line. Under 12V they do not start. I even checked the optocouplers, maybe they are defective, but no. They are also fine.
      Edit: T902 is the zero voltage detector transformer.
      Last edited by yohnsee; 10-14-2018, 10:33 PM.
      Cheers, Janos

      Comment


        #4
        Re: 715G3812-P02-H20-003D Philips TV power supply

        Hello everyone,
        I am back again with this TV.
        I could not figure out the problem with the power supply, so I ordered replacement. I could get my hands on 2 psu's, one is exactly the same as mine, the other one differs a little, but the voltages, ampers, form factor is the same.
        Both new psu acts the same as the old one in the TV, so I am confident to say, all my power supplies are fine. I ordered a new mainboard, because I was not able to troubleshoot that either.
        Only one thing perplexes me. How can I start the power supplies on the bench, out of the TV? I connected the 5V standby trough a resistor back to the STBY pin, it didn't move. Then I added an other resistor from 5V standby to ENA pin, still nothing. So far this is the first power card, that I can't start on its own with resistors. Could anyone help me out? I am very curious.
        Thanks
        Cheers, Janos

        Comment


          #5
          Re: 715G3812-P02-H20-003D Philips TV power supply

          Originally posted by yohnsee View Post
          Hello everyone,
          I am back again with this TV.
          I could not figure out the problem with the power supply, so I ordered replacement. I could get my hands on 2 psu's, one is exactly the same as mine, the other one differs a little, but the voltages, ampers, form factor is the same.
          Both new psu acts the same as the old one in the TV, so I am confident to say, all my power supplies are fine. I ordered a new mainboard, because I was not able to troubleshoot that either.
          Only one thing perplexes me. How can I start the power supplies on the bench, out of the TV? I connected the 5V standby trough a resistor back to the STBY pin, it didn't move. Then I added an other resistor from 5V standby to ENA pin, still nothing. So far this is the first power card, that I can't start on its own with resistors. Could anyone help me out? I am very curious.
          Thanks
          So when you connect the S/B pin to 5VSTBY pin with resistor to test the power supply board by itself, what is the Value of the resistor? 1K Ohms, if it is then what DCV do you get between the two legs of the main filter cap?
          Never stop learning
          Basic LCD TV and Monitor troubleshooting guides.
          http://www.badcaps.net/forum/showthr...956#post305956

          Voltage Regulator (LDO) testing:
          http://www.badcaps.net/forum/showthr...999#post300999

          Inverter testing using old CFL:
          http://www.badcaps.net/forum/showthr...er+testing+cfl

          Tear down pictures : Hit the ">" Show Albums and stories" on the left side
          http://s807.photobucket.com/user/budm/library/

          TV Factory reset codes listing:
          http://www.badcaps.net/forum/showthread.php?t=24809

          Comment


            #6
            Re: 715G3812-P02-H20-003D Philips TV power supply

            Originally posted by budm View Post
            So when you connect the S/B pin to 5VSTBY pin with resistor to test the power supply board by itself, what is the Value of the resistor? 1K Ohms, if it is then what DCV do you get between the two legs of the main filter cap?
            Hello, the resistor is 1k.
            The main filter cap stays at 320V, no matter what I do.
            Cheers, Janos

            Comment


              #7
              Re: 715G3812-P02-H20-003D Philips TV power supply

              Hello again,
              to anyone, who is also stuck with Philips TVs, here are my experiences so far, summarised:
              -you can't start this PSU alone by connecting the stanby voltage back to the start and enable pin. It needs other conditions, which I was not able to figure out, due to lack of time.
              -if it behaves like mine, namely it starts for a brief second with the mainboard, then it is most likely a mainboard problem. I was able to narrow it down to the TCON area, because this board has TCON integrated onto the mainboard.
              This start can easily be seen, as this type of PSU has a dedicated LED on the bottom side of the PCB for the 12V rail.
              Side note: if your mainboard tries to start, but you hear a very faint clicking noise from somewhere around the T-con chip, your first suspect should be U7050, it makes H_VDD from 12V in. Measure the voltage on PIN2, if it is stable 12V but on PIN3 you read anything but 8V, this chip is dead. Be careful when changing, it is connected to a thermal pad beneath, needs a little more heat than usual.
              That's all folks (for now)
              Cheers, Janos

              Comment


                #8
                Re: 715G3812-P02-H20-003D Philips TV power supply

                For future lurckers: to start PSU on the bench, you also need to load the 5V output

                Connect a 1K resistor between 5V and S/B, and a 20R 1W resistor between 5V and GND
                Vdd-S will jump from 5V to 13V
                Last edited by kas49; 07-28-2021, 10:04 AM.

                Comment


                  #9
                  Re: 715G3812-P02-H20-003D Philips TV power supply

                  Hi yohnsee

                  Did you get your tv sorted?
                  Ive got a problem with a damaged PSU board for the same tv
                  I have a blown IC905

                  Can you advise on what IC905 you used to replace?
                  When I search TNY277PN-TL that I found in the service manual I see other codes as well that I don't understand on the ICs

                  Also, because of the Damage to their IC I'm thinking more components are damaged that I haven't found yet

                  Where did you get the replacement PSU board, I cannot find any available anywhere at all

                  Thanks in advance

                  Comment


                    #10
                    Re: 715G3812-P02-H20-003D Philips TV power supply

                    Originally posted by Bobmelapp View Post
                    Hi yohnsee

                    Did you get your tv sorted?
                    Ive got a problem with a damaged PSU board for the same tv
                    I have a blown IC905

                    Can you advise on what IC905 you used to replace?
                    When I search TNY277PN-TL that I found in the service manual I see other codes as well that I don't understand on the ICs

                    Also, because of the Damage to their IC I'm thinking more components are damaged that I haven't found yet

                    Where did you get the replacement PSU board, I cannot find any available anywhere at all

                    Thanks in advance
                    Dear friend,
                    I think I was able to make the TV work, mine had mainboard problem. The PSU was fine, I didn't have the experience back then, and searched the problem where it didn't exist.
                    Back to your panel. TNY277PN is easy to order, I don't know what other codes you have, but the only thing to look out for is the package. I mean, I don't remember if it is an SO-8 SMD package or DIP-8. If these two factors are met, the other codes are not important on the chip, as they mark things like "green product" or "Pb-free", etc.
                    You are most likely right, in such case, when the chip itself blows, other components are affected too. I was lucky back then, I could find a local guy, who also repairs TVs, and he sold PSUs and mainboards second-hand. But if you can't find a replacement anywhere, well, your options are limited to repairing the PSU. Remove IC905, test the other components as well as pcb traces around. You can test the other parts working by disabling the standby circuit on the main side and feeding 5V from a lab bench power supply to the cold side 5VSB with current limit.
                    Cheers, Janos

                    Comment

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