Panasonic Viera TX-P50U20B startup problems

[shimmyshimmy]

Hi,

I recently bought this TV on ebay fairly cheap hoping to be able to repair and use it. The problem is that when the TV is turned on with the main switch I just have a green light and a clicking relay, it clicks 4 times over and over for around a minute then stops. There are no flashing red lights and when I press buttons on the remote the green light flashes as if it is responding to the input. I have tried connecting a source to check for sound but I can hear nothing.

I found a cheap power supply online so decided to try this hoping it would solve the problem, however I have exactly the same symptoms with the replacement supply. I would really appreciate ideas as to my next step, possibly I should test the X sustain and z sustain? Both boards have an LED which is lit does this mean they are working ok? I have some experience testing things with a multimeter so would be fairly confident having a go at troubleshooting this.

Thanks

[tw2005]

Re: Panasonic Viera TX-P50U20B startup problems

Probably need clarification on the startup. So for your model is the normal sequence this.

Power available /standby- solid red LED

Startup - rapid flashing green LED

On - solid green LED

So are you saying it tries to startup, green LED just continuously rapidly blinks and the relays just keep cycling, quits after a minute?

What then, solid green LED, no display or goes back to solid red , standby or does it blink out the red LED a fault code?

Sounding like A-board at this stage.

[shimmyshimmy]

Re: Panasonic Viera TX-P50U20B startup problems

There is no red LED on standby just a green light on startup which flashes rapidly for a few seconds then turns to solid green. As I bought the TV in this state I'm not sure if I should have the red LED on standby or not.

When the relay clicking stops the green LED stays solid, and it only flashes when I press buttons on the remote. Is there a way I can test the A board?

[tw2005]

Re: Panasonic Viera TX-P50U20B startup problems

Yeah, I'm a little lost with noe red standby led but I don't know the UK market. so goes solid green, blinks with the remote, and at this stage are both sustain boards status LEDs lit?, so the panel should be energised.?

Can you see if the panel has a faint glow?, may need a dark room to really notice.

If the TV has been used before, if you hook up the antenna and select Tv and flick though the channels, any audio?

[shimmyshimmy]

Re: Panasonic Viera TX-P50U20B startup problems

I was expecting to see a red light on standby but there is nothing until it is switched on. I can see 2 green LEDs presumably the sustains either side of the tv but this is looking with the back cover still on...I will check with the back off ASAP.

There is definitely no glow from the screen even in a dark room.

I have hooked up my xbox to check for sound but wasn't 100% if I was flicking through the sources with the remote or not. I will connect an aerial to check the built in tuner.

This isn't turning out to be as easy as I'd hoped!

[tw2005]

Re: Panasonic Viera TX-P50U20B startup problems

I have 2 thoughts, bad A-board or cracked panel. I have another idea for the A-board.

I thought if the panel was cracked it would shutdown with sos7 or something but maybe they don't always and might depend on whether the panel is shorted.

Never had this situation before to know, maybe someone else can clarify.

usually there's a video out signal on the a-board. you could hook that up to another TV on av in, select TV on the broken TV, leave the antenna out and the display would normally show a banner regarding no signal.

This should then show up on the other TV through whatever AV in you used. I've done this on an old 2006 panasonic plasma with nil display but appeared to turn on and it output that display.

That was a bad LVDS cable which your Tv won't have but proved the mainboard was working at least. worth a go I guess.

[tom66]

Re: Panasonic Viera TX-P50U20B startup problems

A cracked panel would normally lead to the MID voltage falling due to changes in panel resonance. This would cause LEDs to go out.

[tw2005]

Re: Panasonic Viera TX-P50U20B startup problems

A cracked panel would normally lead to the MID voltage falling due to changes in panel resonance. This would cause LEDs to go out.

it's a strange one, have you struck anything like this? Would you expect with both sustains on, surely some signs of the panel being on. Weird?

[tom66]

Re: Panasonic Viera TX-P50U20B startup problems

The 2011 series Panasonic have very deep black levels. It's also possible the A board goes into dynamic/vivid mode with no input, which can sustain the panel but cut black down to <0.001cd/m^2 (pretty much invisible) on scenes where there is only black or dim pixels, MID voltage will still be there, it only sustains the 1SF (LSB of image.)