50PB560B -LG common problems?

[jp_fizzer]

Re: 50PB560B -LG common problems?

Is there any known way to test the logic board? It looks like I could buy one for around $50 with shipping but it would be kind of nice to confirm that it was the problem before spending this.

[dick_barton]

Re: 50PB560B -LG common problems?

If the set powers up and all the voltages appear to be correct and if we ignore Vsc for a moment, what you do know is that the set will not go into self-test mode, then perhaps there's a problem with the Logic board.

[jp_fizzer]

Re: 50PB560B -LG common problems?

Here is where I am measuring Vsc on the Y buffer board. You can see from the picture that I get -23VDC when the TV is powered up but not working and I get 113VAC when the TV is working. Now the 113VAC does not seem to be related to the line voltage because I have tried it plugged into both 110V mains and 220V mains and this Vsc voltage reads the same.

Does this Vsc voltage provide any clues about what could be the problem?

Any suggestion what to test next? I have left the TV on in case there are any tests while it is on. As soon as I turn it off it will take many tries to get it to come back on again.

[dick_barton]

Re: 50PB560B -LG common problems?

All your voltages appear to be good other than Vsc whcih I'm unsure how or where you measure it. Hopefully someone else can provide an answer.
The other person did get the test pattern to run so I'm suspicious of your logic board.
At this point I am out of any further ideas but hope you get some more help from other forum users.

[jp_fizzer]

Re: 50PB560B -LG common problems?

Here is the white label

[jp_fizzer]

Re: 50PB560B -LG common problems?

Just seen this in another post relating to this model. To run the self test successfully

Ok, I tried what the other poster did. I unplugged both the ribbon cable between control board and main board as well as the cable between power supply board and main board, inserted the jumper and plugged in TV. Nothing happened.

Then I connected everything back up again and the TV turned on. Since it was powered up I retested the voltages on the Y buffer board. The Vy is still 190V but the Vsc is very strange. When I put red probe on Vsc and black on chassis the meter just bounces on DC setting so I tried switching to AC and it is pretty steady around 120VAC, which is the line voltage I am plugged into. I switched back to DC and reversed the probes so black on Vsc and red on chassis, it is bouncing around 6-8 VDC.

Edit: I re-tested Vsc, this time using my Fluke T5 which has voltage autoselection and it is giving me 113VAC, so definitely it is thinking it is AC basically line voltage. This is while the TV is working.

[dick_barton]

Re: 50PB560B -LG common problems?

Just seen this in another post relating to this model. To run the self test successfully

Originally Posted by tvtimmy View Post
Unplug the ldvs cable(flat one) that runs from the Main board to the control board and put a piece of wire in the holes on control board marked r451 and r452. If you have test patterns and colored screens your main board is bad.

Hi, did what you suggested, and still wouldnt turn on, so unplugged the cable from PSU to main board, and it turned on, then did what you said and got test patterns

[dick_barton]

Re: 50PB560B -LG common problems?

That seems awful low but I'm unfamiliar with the layout of this buffer. Normally it is measured across a resistor.
Perhaps someone else could offer advice here.

The only other thing is to try and get the set two switch on again and then measure +Vsc once again.

The white label on the back of the panel can you post a picture of it because it does give information.

[jp_fizzer]

Re: 50PB560B -LG common problems?

Ah found it. Vsc to gnd is -23.5V

[dick_barton]

Re: 50PB560B -LG common problems?

What do you have for +Vsc to chassis

[jp_fizzer]

Re: 50PB560B -LG common problems?

I could not find the Vsc and Ve voltages. The Vy is 190V. Attached are pics of the Y buffer board.

[dick_barton]

Re: 50PB560B -LG common problems?

What voltage do you have across the two pins marked -Vy+ on the Ybuffer board. Place your meter black lead to - and red to +

[jp_fizzer]

Re: 50PB560B -LG common problems?

All of the voltages are the same when it does power up as when it does not power up

[dick_barton]

Re: 50PB560B -LG common problems?

You need to check that all the voltages are correct or if any are missing when the set fails to power up.

[jp_fizzer]

Re: 50PB560B -LG common problems?

After I plugged the ribbon cable in then I was able to get the TV to turn on. However, as soon as I cycle the power it no longer works.

It used to be that if I cycled the power several times eventually it would work. However that method stopped working a week ago so I decided to take the back off and see if I could figure out the problem. There was no obvious damage. I disconnected and reconnected all of the connectors from the power board and main board and then it worked again, once. As soon as I turned it off it would not turn back on again. Then I removed the ribbon cable and have reconnected it and again the TV turned on again once. But as soon as I turn it off it will no longer turn on.

[dick_barton]

Re: 50PB560B -LG common problems?

Then I would look very carefully at the ribbon cable you disconnected and confirm it has been correctly inserted. That's the only thing that you have removed to carry out the test above.

[jp_fizzer]

Re: 50PB560B -LG common problems?

Yes, I just checked and I have VS on both pins 1 and 2 and I have VA on pin 6

[dick_barton]

Re: 50PB560B -LG common problems?

Do you have VS & VA when you power up?

[jp_fizzer]

Re: 50PB560B -LG common problems?

Now I have plugged the ribbon cable back in and turned on the TV and it worked fine. I turned it off and now it won't turn on again, although the standby light will switch.

[jp_fizzer]

Re: 50PB560B -LG common problems?

Ok, I unplugged TV, removed ribbon (you are correct, black tab lifts from left), inserted paperclip between two holes, plugged in TV.

The standby light came on but that was all. I tried turning the TV on and off several times but all that did was toggle the standby light, the screen never came on.