50PB560B -LG common problems?

[jp_fizzer]

Re: 50PB560B -LG common problems?

Oh wow, I am really glad I did not bake the boards.

So I see now why the 55V is correct on pin#6 of P811. That pin corresponds to VA which is supposed to be 55V.

Attached are photos of P811 and P813 (which is just the other end of P600 so they are exactly the same) and also a photo showing what the VS and VA voltages are supposed to be.

So the fact that when the TV is working properly pin#6 on P811 is the correct 55V but when the TV is not working properly it is 0V, does this tell me anything useful?

[Unspun01]

Re: 50PB560B -LG common problems?

...did some more trouble shooting with the schematics in hand and found that the mosfet was not turning on or off . The mosfet supplies 5v from the 5v-stb which goes on to provide 3.3v 1.8v 1.15 volt.This is the mosfet I jumpered which seems to have restored most of the functionality.The mosfet is Q604 and is switched by Q603 an NPN transistor.Jumpering the Drain AND Source of Q604 is what gave the set functionality again..

Helikvar:

Thanks for posting this information.

I can confirm that your information is good.

I have also repaired a 60PB5600 plasma mainboard similar to 50PB560B in this same manner. For anyone who is interested, here is a summary of the symptoms with my TV and the fix:

Bad mainboard. Initial issue: Has power, will respond to power button and turn on, but no image or menu. Can't turn off once turned on.

Replaced broken HDMI port, replaced MMBT3906 PNP transistor (Q203?), replaced 10k smt resistor.

Was still dead - No power. Replaced -30V, -4.3A SOT23 P-channel FET AO3407A (Q604) (LG part EBK60752501), and now TV turns on.

I got the transistor from an old scrap 37LD450 mainboard (Q409).

Hope this helps someone.

[dick_barton]

Re: 50PB560B -LG common problems?

There was a huge spark when I plugged in the P811 connector but when I turned the TV back on this time it came back on.

In addition I would also check the pins on P801 plug and connector for any damage due to sparking.

[jp_fizzer]

Re: 50PB560B -LG common problems?

Attached are photos of the back of the TV and a closeup of the Logic Board.

I really only see two small next to R451 and R452 and below it is a pad labelled Auto.

I am actually not really sure how to release that ribbon connector that goes to the main board. I assume I lift a clasp and then the ribbon cable will pull out but I cannot figure out what I am supposed to lift. I tried both the black plastic part and the silver metal part and neither want to lift easily. I figured I better ask before I break something.

[Unspun01]

Re: 50PB560B -LG common problems?

So I unplugged all the boards again and plugged them back in. There was a huge spark when I plugged in the P811 connector but when I turned the TV back on this time it came back on. I have checked all the voltages with the TV on and they are all the same except that pin#6 on P811 is now at 55V where as it was 0V when the TV was plugged in but not working. Is this the key? Does anybody know what that might mean?

The huge spark is a result of plugging in the cable when capacitors were not completely discharged. Possibly the VA supply (approx 60V) or the VS supply (approx 210V). Try to avoid doing this as it can scare you and it is damaging to your TV. You can use a 1W-5W ceramic 1kohm resistor to safely discharge power supply voltages (VA-gnd or VS-gnd)

[Unspun01]

Re: 50PB560B -LG common problems?

I really only see two small next to R451 and R452 and below it is a pad labelled Auto.

I am actually not really sure how to release that ribbon connector that goes to the main board. I assume I lift a clasp and then the ribbon cable will pull out but I cannot figure out what I am supposed to lift. I tried both the black plastic part and the silver metal part and neither want to lift easily.

Yes the two pins labelled AUTO are the ones you need. Jumpering these pins with mainboard disconnected and plugging in the tv should let the tv turn on and display test patterns if panel and panel boards are working. It helps you isolate mainboard issues.

Gently lift the black plastic part with fingernail and gently remove ribbon cable by pulling to the right. Very little force is required. If you need force you are doing something wrong and should re-evaluate before breaking something.

[jp_fizzer]

Re: 50PB560B -LG common problems?

Ok, so I am trying to connect the two holes, basically I want to connect the copper rings around the holes to each other?

For the black connector, am I slipping my fingernail under the ribbon edge (right side) and lifting, or the circuit board (left) side?

[Unspun01]

Re: 50PB560B -LG common problems?

Yes, connecting the copper rings of the holes. Paperclip will apply gentle spring pressure to hold in place. Don't insert too deep - you don't want to accidentally contact other ground points.

Lift black plastic from circuit board side I thing. Look closely at it. You should see a hinge appearance and it should be obvious how it opens.

[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.

[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.

[dick_barton]

Re: 50PB560B -LG common problems?

Do you have VS & VA when you power up?

[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?

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?

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?

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?

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?

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?

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 do you have for +Vsc to chassis

[jp_fizzer]

Re: 50PB560B -LG common problems?

Ah found it. Vsc to gnd is -23.5V