Panasonic TH-42PV8AZ with no STB_5V

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  • Neelix
    Senior Member
    • Oct 2013
    • 145
    • South Africa
    #1

    Panasonic TH-42PV8AZ with no STB_5V

    I got a Panasonic TH-42PV8AZ plasma here that does not power on at all. Power switch is on, but there is no standby light and I measure on output of the power board and there is no STB_5V which would explain why there is no standby light. I measure on the pins of microcomputer IC501 for the power board and get the next voltages:

    pin 01(VDD) - 5Vdc
    pin 02(VSS) - 0Vdc
    pin 03(XIN) - waveform look good on scope
    pin 04(XOUT) - waveform look good on scope
    pin 06(RST) - 5Vdc
    pin 07(STB_PS_ON_H) - 5Vdc
    pin 09(STB_5V_ON_L) - 2.9Vdc
    pin 20(STB_5V_OFF_L) - 5Vdc
    pin 21(AC_FAIL_H) - 0.6Vdc
    pin 23(AC_DET/F_STB_H) - 0Vdc

    I don't see any other pins on IC501 that could influence the STB_5V. At pin 9 there should be 0V(as indicated by the L in the pin description) to switch on Q521 and Q537 to get STB_5V at the output of the power board, but instead there is 2.9V. Any ideas or somebody come across this before?
    Last edited by Neelix; 10-09-2014, 06:46 AM.
    Tags: None
    • tom66
      EVs Rule
      • Apr 2011
      • 32560
      • UK
      #2
      Re: Panasonic TH-42PV8AZ with no STB_5V

      Do you get a 50/60/100/120Hz square wave on the AC_DET line?
      If not, use a bit of freeze spray on the module that generates that signal (it's the board with two optocouplers) - spray the primary side. Does TV power on?
      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

        • Neelix
          Senior Member
          • Oct 2013
          • 145
          • South Africa
          #3
          Re: Panasonic TH-42PV8AZ with no STB_5V

          Hello Tom. I don't get any square wave at AC_DETECT pin. Attach is photo of the power board from the top. The board don't have modules like I have seen with other Panasonic power boards
          Attached Files

            Comment

            • tom66
              EVs Rule
              • Apr 2011
              • 32560
              • UK
              #4
              Re: Panasonic TH-42PV8AZ with no STB_5V

              Do you have a schematic for this board...?
              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

                • Neelix
                  Senior Member
                  • Oct 2013
                  • 145
                  • South Africa
                  #5
                  Re: Panasonic TH-42PV8AZ with no STB_5V

                  Attach is service manual I downloaded from ElektroTanya
                  Attached Files

                    Comment

                    • Neelix
                      Senior Member
                      • Oct 2013
                      • 145
                      • South Africa
                      #6
                      Re: Panasonic TH-42PV8AZ with no STB_5V

                      I replaced microcomputer IC501, but still no STB_5V. Luckily I now have another TV here with same power board and can compare voltages. Makes life easier when you have a another board to compare with

                        Comment

                        • Neelix
                          Senior Member
                          • Oct 2013
                          • 145
                          • South Africa
                          #7
                          Re: Panasonic TH-42PV8AZ with no STB_5V

                          The reset capacitor was the culprit. TV working now

                            Comment

                            • tom66
                              EVs Rule
                              • Apr 2011
                              • 32560
                              • UK
                              #8
                              Re: Panasonic TH-42PV8AZ with no STB_5V

                              Which capacitor was that? Reference number?
                              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

                                • Neelix
                                  Senior Member
                                  • Oct 2013
                                  • 145
                                  • South Africa
                                  #9
                                  Re: Panasonic TH-42PV8AZ with no STB_5V

                                  The capacitor is in the reset circuit for IC501, the micro of the power board. The reference number is C519

                                    Comment

                                    • tom66
                                      EVs Rule
                                      • Apr 2011
                                      • 32560
                                      • UK
                                      #10
                                      Re: Panasonic TH-42PV8AZ with no STB_5V

                                      Useful info, thanks!
                                      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

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