LG 50PG6000 No Picture with sound, and boards seem OK

[ilkatek]

Hello there.
I have the LG plasma mentioned in the title and the problem is that
the tv display will not show any image not even the menu. Thought it could be the Ysus board or buffer board or power board or Zsus board. Started from power board, changed a suspect cap. all others seemed ok. Went on to the Ysus board and also changed a blown cap 3300microF/10V with same value but 16 V. Made a general check to see if the boards (Ysus, Zsus, power board, buffer boards) were shorted by testing (ohm) between ground and input/output pins and tested each FET for shorted legs not only in OHM – beep mode but also in diode mode to see values, all readouts from DMM were around 350 or over so all seem to be OK.
Mounted everything back but still had sound but no picture. I then checked all voltages and they all correspond to the values printed just beside the connectors and the sticker (Va 195, Vs 65, and voltages such as 5, 12, 24) all normal. I also measured the voltage on the pins of the connectors that feed the display from the buffer with the 4 twin ribbon cables and found 58V on all pins that are supposed to have tension. I am not sure if such value (58V) is correct since I could not find any clue to that not even on the service manual (BTW the service manual is useless the philosophy in it is of the type “if the lamp does not turn ON check to see if the plug is attached to the socket” ...LOL).
So figuring that it may be the plasma display it self that is broken or the processor needs to be reprogrammed?. So I tried by holding for approx 5-10sec a button that seemed to be something like a reset button placed on the peripheral inlet board and also by holding it during switching ON the TV. In both cases the TV just resets by turning Off and back On again but nothing changed. The black screen is still there.
Any ideas ????

[Ltank]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

If all the voltages are good. Try this. Normally on a Plasma Control board there are a jumpers to make the set display a series of test patterns. If this works, I highly suspect the main boad.

[ilkatek]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

Hello Ltank
Thanks for taking the time to answer me. I cannot find such jumpers on the ctrl board unless you mean the two small white connection points with 4pins each (shown on the photo) but they seem to be some kind of dedicated (serial?) connections for specialized service. Nevertheless I will build a null-modem to connect to the serial db9 connector on the back of the set and try to update or even reload the firmware. Do you think there could be some chance on fixing the problem that way?

(Facing some issues on trying to attach images, maybe I am not entitled to do so)

[Hamie]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

There are more voltages than vs and va.


You need to check vsc and -vy located on the y-sus.
And also check z-bias on the z-sus.

They should match the panel sticker like this.

[Hamie]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

[ilkatek]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

Hello Hamie thanks for replying,
As I initially posted, all voltages seemed to be OK, in fact they were, but when I red your message I just wanted to go back and check them again. ...this time, (besides the Zbias which is OK (100v) and of course the Va and Vs), the Vy and Vsc were 0V across the relative test resistance and around 52 compared to ground. Since I was sure that previously I had found them correct I just detached the 2 buffer boards and in fact now the voltages are again correct across the test resistances -190 Vy and 135 Vsc.
Finally I am at a point. This would mean that the buffer boards need to be changed but since its my 1st time trying to fix a plasma TV my question is: Will it be sufficient to change the buffer boards or maybe the display has gone dead? Is there any way to test it beforehand?

[ammarben]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

the buffer boards need to be checked first

[ilkatek]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

What do you mean ammarben? I see that there is not so much to check on the buffer boards, the ic´s are covered with the heatsink which is glued on the board. When I place them back and connect them to the Ysus board with or without the ribbon cables going to the display, the Vyand Vsc go again to 0V.

[ammarben]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

see in youtube https://www.youtube.com/watch?v=51SZsfH60EY

[ilkatek]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

Thank you all for your precious help.
Solved! ...well at least I know exactly where the problem is.
I have seen the link you gave me ammarben and after a check on my 2 Ybuffers I found one Cip of the lower buffer being shorted. I then mounted back only the good buffer and as expected only half video was displayed. But that was a success since I now know also that the display is functioning. Since it seems quite odd to try and change the single Cip as the pins are too close to one another) I will search to buy the lower buffer .
But I have a doubt on which of the following marks are relevant for searching on Internet. There are 3 marks that I think could be relevant but which one should I be looking for? Since I have noticed that finding a mark the other two or even one of them may not comply.
50G1_YDB
EAX-39636901
EBR-38374803

[mmservice]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

I've the same problem on a 50PA4500 Tv. As you have described I've checked the Va and Vs, and the other voltages on the power supply an they seem ok. But on the Ysus board the Vsc and Vy aren't regular. I've tested for short all the outputs of the two y-buffer, but no fault was found. So I think the faulty board should be the ysus. Can I test the ysus without the y-buffers boards connected to view if the Vsc and Vy go on their regular values or not? Are there other tests that I can make?

[Hamie]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

I've the same problem on a 50PA4500 Tv. As you have described I've checked the Va and Vs, and the other voltages on the power supply an they seem ok. But on the Ysus board the Vsc and Vy aren't regular. I've tested for short all the outputs of the two y-buffer, but no fault was found. So I think the faulty board should be the ysus. Can I test the ysus without the y-buffers boards connected to view if the Vsc and Vy go on their regular values or not? Are there other tests that I can make?

Yes disconnect the buffers

[mmservice]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

ok pulled out the two buffer boards, the Vsc and Vy go to the nominal values. I've found the bottom y-buffer board have some output pins shorted with the positive rail, in the first test I've checked them only in respect the gnd. And this was my error. I think that the problem is solved, but I'm waiting to have the new board for the final tests

[ilkatek]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

Hello mmservice, did you solve the problem? I have solved by detaching the bad cip and I placed back the buffer. Now the TV will not show the lower strip of the monitor image but it doesn't matter since all the films I watch with this set (I use this set only for registered films) has the upper and lower strip blanked anyway from the film format. So I will keep it as it is until some other cip fails and then I will go with the repair (unless the upper cip brakes )

[Alastair E]

Re: LG 50PG6000 No Picture with sound, and boards seem OK

If -Vy and VSC return to normal without the buffers connected, then there's a dead buffer chip, Easy to locate which one by resistance tests.

Instead of trying to find a complete buffer board, Why not just change the faulty chips...?