TV Sharp LC 37D42U (DPS 178AP)

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  • jdnation
    Member
    • May 2020
    • 10
    • Venezuela

    #1

    TV Sharp LC 37D42U (DPS 178AP)

    Hi every one! i have a tv Sharp Model: LC 37D42U, witch have a DELTA power supply DPS 178AP

    At first i had a bad power supply and the tv didn't have standby power (BUS 5Vdc) checking the board i realized that the two main MOSFET P16NS25 were shorted.

    So i buy another one, it wasn't brand new so i trust the guy who sell it to me that it was good. Now i just connect the new board and i have stand by power (Bus 5Vdc), but now i have the power and opc led flashing one time and then only the power led flashing on time.

    I've been investigating and the service manual tells me that flashing patron means that i have a UR13V problem.

    So i measure UR13 pin and i have nothing and the 24V for the inverter board i have nothing too.

    I also did the pressing the vol up y ch down button thing too. And the only thing it does is that the power led stays on nothing else. With this scenario i measure all the voltages again and have the same result.

    Can anyone give me some advice? what can i check? Maybe if this board is bad i can fix it with components of the old one?
    Jairo Morales
  • nomoresonys
    Badcaps Legend
    • Jan 2013
    • 12137
    • U.S.

    #2
    Re: TV Sharp LC 37D42U (DPS 178AP)

    Maybe try UNHOOK the PD 6 pin connector from powerboard to mainboard, use about a 1k resistor to jump PS-ON to BU5V, plug power cord into powerboard, see if you have the 12 v and other voltages that are missing.

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    • jdnation
      Member
      • May 2020
      • 10
      • Venezuela

      #3
      Re: TV Sharp LC 37D42U (DPS 178AP)

      Originally posted by nomoresonys
      Maybe try UNHOOK the PD 6 pin connector from powerboard to mainboard, use about a 1k resistor to jump PS-ON to BU5V, plug power cord into powerboard, see if you have the 12 v and other voltages that are missing.
      I did that, and the voltage appears but only for a second, then ti goes down to zero
      Jairo Morales

      Comment

      • jdnation
        Member
        • May 2020
        • 10
        • Venezuela

        #4
        Re: TV Sharp LC 37D42U (DPS 178AP)

        Update:

        Searching the internet i found the squematic diagram (Page 25 of the attachemnt) of the PSU. i've been studying it but can figure out what going on
        Attached Files
        Jairo Morales

        Comment

        • R_J
          Badcaps Legend
          • Jun 2012
          • 9535
          • Canada

          #5
          Re: TV Sharp LC 37D42U (DPS 178AP)

          Since you have standby BU5V, also check if you have voltage on Q7900 collector (18~25vdc) Then with the power supply turned ON, check if you have VCC & VCC_ON
          If Q7602 & Q7603 were shorted, check the gate diodes and resistors, I suspect if the fets shorted drain to gate, the ic7603 is also defective
          Last edited by R_J; 05-28-2020, 06:32 PM.

          Comment

          • jdnation
            Member
            • May 2020
            • 10
            • Venezuela

            #6
            Re: TV Sharp LC 37D42U (DPS 178AP)

            Originally posted by R_J
            Since you have standby BU5V, also check if you have voltage on Q7900 collector (18~25vdc) Then with the power supply turned ON, check if you have VCC & VCC_ON
            If Q7602 & Q7603 were shorted, check the gate diodes and resistors, I suspect if the fets shorted drain to gate, the ic7603 is also defective
            About Q7602 and Q7603 those were shorted in the old board, i get another one. This one seems find and the mosfet in this one are okey but i think this one have some other problem

            Sorry i couldn't find that transistor (Q7900), i found Q7901 and Q7902

            Q7901:
            Ve= 0.535Vdc (VCC-ON)
            Vb= 0.535Vdc
            Vc= 0.00 Vdc

            Q7902:
            Ve= 0.535Vdc (VCC)
            Vb= 0.835Vdc
            Vc= 22.7 Vdc

            Thanks for the help!
            Last edited by jdnation; 05-28-2020, 06:53 PM.
            Jairo Morales

            Comment

            • R_J
              Badcaps Legend
              • Jun 2012
              • 9535
              • Canada

              #7
              Re: TV Sharp LC 37D42U (DPS 178AP)

              I was looking at the poor schematic, so it would be Q7902. Q7902 has 23v on the collector which is ok, to get the 15 volts on the emitter, the base needs to be turned on by the optocoupler IC7902, You need to have the power supply board turned ON to get the vcc voltage, so if the board is out of the tv, you can connect BU5V to PS_ON tu turn on the board. This should turn on Q7301 and Q7302 which turns on the (led) in the optocoupler of ic7902.
              Last edited by R_J; 05-28-2020, 07:08 PM.

              Comment

              • jdnation
                Member
                • May 2020
                • 10
                • Venezuela

                #8
                Re: TV Sharp LC 37D42U (DPS 178AP)

                Originally posted by R_J
                I was looking at the poor schematic, so it would be Q7902. Q7902 has 23v on the collector which is ok, to get the 15 volts on the emitter, the base needs to be turned on by the optocoupler IC7902
                Yes that's right!

                but the optocoupler have 0.615V on the anode, i measure D7301 and its voltages are = C: 0.615Vdc, A:0.777Vdc

                Then i measure R7306 and its voltages are 4.92Vdc and 0.777Vdc.

                I think the problem is in the circuit that controls the gate of Q7304. But i really don't understand that circuit.
                Attached Files
                Last edited by jdnation; 05-28-2020, 07:17 PM.
                Jairo Morales

                Comment

                • R_J
                  Badcaps Legend
                  • Jun 2012
                  • 9535
                  • Canada

                  #9
                  Re: TV Sharp LC 37D42U (DPS 178AP)

                  That looks like an over voltage/over current protection circuit, if any of the voltages are too high such as UR6V, then D7315 conducts and turns on the Q7304 SCR. The SCR turns ON shorting out ic7902 turning off the supply. Now this might happen if you are testing the board out of the tv without a load on the supplies. You did say the voltage appears for a second then drops
                  The over current part is ic7302, it monitors the current (UR6V is monitored across R7401) the "D" "D" So you could have a high load on one of the supplies IE INV24 (bad inverter board?)
                  Last edited by R_J; 05-28-2020, 07:40 PM.

                  Comment

                  • jdnation
                    Member
                    • May 2020
                    • 10
                    • Venezuela

                    #10
                    Re: TV Sharp LC 37D42U (DPS 178AP)

                    Originally posted by R_J
                    That looks like an over voltage/over current protection circuit, if any of the voltages are too high such as UR6V, then D7315 conducts and turns on the Q7304 SCR. The SCR turns ON shorting out ic7902 turning off the supply. Now this might happen if you are testing the board out of the tv without a load on the supplies. You did say the voltage appears for a second then drops
                    The over current part is ic7302, it monitors the current (UR6V is monitored across R7401) the "D" "D" So you could have a high load on one of the supplies IE INV24 (bad inverter board?)
                    Ok ok i understand that, so what should i do?, how can i test the inverter board?
                    Jairo Morales

                    Comment

                    • R_J
                      Badcaps Legend
                      • Jun 2012
                      • 9535
                      • Canada

                      #11
                      Re: TV Sharp LC 37D42U (DPS 178AP)

                      That was just an example, you could have a high load on one of the other supplies, You could try unpluging the inverter board and see if the tv turns on without backlight.

                      Comment

                      • jdnation
                        Member
                        • May 2020
                        • 10
                        • Venezuela

                        #12
                        Re: TV Sharp LC 37D42U (DPS 178AP)

                        Originally posted by R_J
                        That was just an example, you could have a high load on one of the other supplies, You could try unpluging the inverter board and see if the tv turns on without backlight.
                        I just made the test and nop, the tv still doing the led flashing thing
                        Jairo Morales

                        Comment

                        • dick_barton
                          Badcaps Legend
                          • Aug 2015
                          • 6642
                          • Wales

                          #13
                          Re: TV Sharp LC 37D42U (DPS 178AP)

                          What voltage do you have on PD pin 2 (AC_DET). It should be between 2.9V to 3.3V according to the schematic given above.
                          Willing to help but I'm no expert.

                          Comment

                          • jdnation
                            Member
                            • May 2020
                            • 10
                            • Venezuela

                            #14
                            Re: TV Sharp LC 37D42U (DPS 178AP)

                            Originally posted by dick_barton
                            What voltage do you have on PD pin 2 (AC_DET). It should be between 2.9V to 3.3V according to the schematic given above.
                            Here are the measure of the PD socket

                            1.- Measurements doing the VolUP-CHdown thing
                            GND = 0 Vdc
                            BU5V = 5.09 Vdc
                            PNL POW = 1.1 mVdc
                            GND = 0 Vdc
                            AC_DET = 3.09 Vdc
                            PS-ON = 3.02 Vdc

                            2.-Measurement when the TV is doing LED flashing thing
                            GND = 0 Vdc
                            BU5V = 5.09 Vdc
                            PNL POW = 0 Vdc
                            GND = 0 Vdc
                            AC_DET = 3.09 Vdc
                            PS-ON = 0 Vdc
                            Jairo Morales

                            Comment

                            • dick_barton
                              Badcaps Legend
                              • Aug 2015
                              • 6642
                              • Wales

                              #15
                              Re: TV Sharp LC 37D42U (DPS 178AP)

                              I know that you have been asked to do this already but can you repeat the test.

                              Disconnect the main board from the power supply and connect BU5V using a 1K resistor to PS_ON and a second 1K resistor from BU5V to PNL_POW

                              Check you have 24V and what voltages you have at connector PE

                              What dc voltage do you have with the meter measuring across the two legs of C7001

                              The resistors must be kept in place while you run these tests.
                              Last edited by dick_barton; 05-29-2020, 03:41 PM.
                              Willing to help but I'm no expert.

                              Comment

                              • jdnation
                                Member
                                • May 2020
                                • 10
                                • Venezuela

                                #16
                                Re: TV Sharp LC 37D42U (DPS 178AP)

                                UPDATE!

                                I found the problem! it seems like the board got bend during shipping!. checking a circuit (i was checking values and continuity of all components) i found that i was getting a problem with IC76002, so i found out it didn't have continuity between its anode and the resistor R7629

                                I check real close the board and finally see that it was a little (minimal) bend, so keep checking and found were the conductive track were broken, now i just made a little soldering and test again the board! and BUMM it finally worked!! then i connected to main board and inverter and it works!!



                                Thanks everyone for the help!
                                Attached Files
                                Jairo Morales

                                Comment

                                • dick_barton
                                  Badcaps Legend
                                  • Aug 2015
                                  • 6642
                                  • Wales

                                  #17
                                  Re: TV Sharp LC 37D42U (DPS 178AP)

                                  Glad you got there in the end.
                                  Willing to help but I'm no expert.

                                  Comment

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