Panasonic TH-42PV8AZ with no STB_5V

[Neelix]

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?

[tom66]

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?

[Neelix]

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

[tom66]

Re: Panasonic TH-42PV8AZ with no STB_5V

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

[Neelix]

Re: Panasonic TH-42PV8AZ with no STB_5V

Attach is service manual I downloaded from ElektroTanya

[Neelix]

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

[Neelix]

Re: Panasonic TH-42PV8AZ with no STB_5V

The reset capacitor was the culprit. TV working now

[tom66]

Re: Panasonic TH-42PV8AZ with no STB_5V

Which capacitor was that? Reference number?

[Neelix]

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

[tom66]

Re: Panasonic TH-42PV8AZ with no STB_5V

Useful info, thanks!