Panasonic LCD tv goes into standby and won;t display a picture

[Acerman]

This Tv is a Panasonic tx42a400. It will not display a picture or sound. The tv powers on but the green power LED quickly turns to a red flashing LED and the tv stays on standby. There are some signs of life on the screen initially soon after powering on. You can clearly see backlight activity , but this soon goes off and then the tv shuts down to standby. I have changed the power board as I thought that this was the cause of the problem. Also used different cables etc. I now suspect the main av board and wanted to know if anyone can suggest some voltage testing to check the av board before I buy a replacement av board.

[dick_barton]

Re: Panasonic LCD tv goes into standby and won;t display a picture

If you could post some photo's of your boards and how they are interconnected would be a good starting point.

[Alastair E]

Re: Panasonic LCD tv goes into standby and won;t display a picture

How many blinks?

[ReeceyBurger123]

Re: Panasonic LCD tv goes into standby and won;t display a picture

Check my thread out likely led failed:

https://www.badcaps.net/forum/showthread.php?t=54714

Also do some research yourself on how to test voltages the forum is full of advise in previous threads.

[Andrew F. Ali]

Re: Panasonic LCD tv goes into standby and won;t display a picture

check my thread out likely led failed:

https://www.badcaps.net/forum/showthread.php?t=54714

also do some research yourself on how to test voltages the forum is full of advise in previous threads.

+1

[Acerman]

Re: Panasonic LCD tv goes into standby and won;t display a picture

Alistair e. The tv just seems to blink repeatedly without a pause.

[Acerman]

Re: Panasonic LCD tv goes into standby and won;t display a picture

dick barton, I will get some photos on here asap if I can.

[Acerman]

Re: Panasonic LCD tv goes into standby and won;t display a picture

I get the basic principle. Use the metal back chasis of the lcd panel as ground and then use the red probe to test the voltage.

[Acerman]

Re: Panasonic LCD tv goes into standby and won;t display a picture

Thanks reecyburger. Very useful link. SO you think, maybe a faulty led strip or individual led. You may be right as I have now repaced both the main board and the psu board and the fault persists.

[dick_barton]

Re: Panasonic LCD tv goes into standby and won;t display a picture

What's the part number printed on the power supply. It's too out of focus to see anything clearly.

[Acerman]

Re: Panasonic LCD tv goes into standby and won;t display a picture

Part number for the psu is TNPA5916

[dick_barton]

Re: Panasonic LCD tv goes into standby and won;t display a picture

Assuming that your power supply is OK, do the backlights come on and remain on if you power up with the mainboard disconnected.

[dick_barton]

Re: Panasonic LCD tv goes into standby and won;t display a picture

Does this set also have a led driver board??

[Acerman]

Re: Panasonic LCD tv goes into standby and won;t display a picture

Yes, it does have an led driver board. Have tried changing it as I have a spare, but made no difference.

[Acerman]

Re: Panasonic LCD tv goes into standby and won;t display a picture

Assuming that your power supply is OK, do the backlights come on and remain on if you power up with the mainboard disconnected.

No. The led goes red and it goes to standby, but the backlights definately don't come on. This was with the lvds cable disconnected from the main board.

[dick_barton]

Re: Panasonic LCD tv goes into standby and won;t display a picture

To check the backlights then disconnect the mainboard from the power supply and connect PS_ON (Power On) to Standby Voltage using a 1K resistor, and also BL_On(backlight on) again to Standby Voltage using 1K resistor.

[Acerman]

Re: Panasonic LCD tv goes into standby and won;t display a picture

Have reconnected the lvds to the mainboard, but now have no backlight activity atall. At first, when this problem started the backlight came on for about 1 second shortly after powering on. Now there is nothing and the tv is on standby with the 1 repeating led flash.

[dick_barton]

Re: Panasonic LCD tv goes into standby and won;t display a picture

What results did you have regarding my earlier post #16

[Acerman]

Re: Panasonic LCD tv goes into standby and won;t display a picture

Haven't done this from 16. I don't have the 1k resistor. Have just reconnected everything.

[Acerman]

Re: Panasonic LCD tv goes into standby and won;t display a picture

To check the backlights then disconnect the mainboard from the power supply and connect PS_ON (Power On) to Standby Voltage using a 1K resistor, and also BL_On(backlight on) again to Standby Voltage using 1K resistor.

Thanks for the help but I am not sure I need to test further. The link from reecyburger shows exactly the same symptoms in another tv from the same series. Also, mine blinks once red followed by a pause. One blink means backlight issue according to Panasonic. I need to decide whether to strip down the panel or not. I am wary of doing that , as I may damage the lcd beyond repair by dismantling everything. It may be worth doing though.