LG 60PH6608 YSUS repair

[maces]

Hello all,

I have a problem with my LG 60PH6608. The TV is only clicking and doesn't get started.
I checked the power supply and measured that the 200V is shorted at the YSUS board.
All IGBTs, the MOSFET K8A60DA and the diode D603 are shorten.
So I replaced the parts. I checked the further parts for shorts and I was pretty sure that there is no further problem on the board.
So I plugged it in. Directly, resistor R251 (2,2 Ohm) blowed out with a little spark. Immediately I disconnected the TV from supply.
I checked the replaced parts (IGBTs, MOSFET K8A60DA and the diode D603), but they all seem to be functional. I'm not sure if I should replace the resistor and try it again. I thing there is a high chance to fail again or to damage further parts. I have no schematic found to check the function of R251.
I would be happy about tipps how to go on.

-Maces

[nomoresonys]

Re: LG 60PH6608 YSUS repair

trace that resistor back to the most likely suspect.

[nomoresonys]

Re: LG 60PH6608 YSUS repair

need to be vigilant in testing, test the buffer boards for shorts, check youtube, theres some videos there.

[nomoresonys]

Re: LG 60PH6608 YSUS repair

example there, find the ground and test them, if they are ok thats good you can eliminate them and concentrate on the Y sus, the reason for testing them is if they are bad they can blow your Y sus and vise versa, thats just one of the reasons I hate plasmas, its SO easy for one bad board to take out a connected good board, happens in other types of tvs too of course but not nearly as often: https://www.youtube.com/watch?v=V6hxf9sARMY

[maces]

Re: LG 60PH6608 YSUS repair

Thank you for the quick and helpful answer. I checked the buffer board for shorts, like it is shown in the video. There is no short, so I assume that the buffer board is OK.
Then I replaced the resistor. I turned the TV on and measured the current trough. It is about 50mA. So I suspect that the resistor was already damaged before.
Now the TV turns on, but there is no picture, only the "backlight" turns on.
From the YSUS board comes a noise, a kind of buzzing. I cannot localize it to a concrete part.

[R_J]

Re: LG 60PH6608 YSUS repair

Note: Plasma TV's do not have a backlight, if the panel is lighting up but has no video, try this:
with the tv off, the control board has two test points labeled EXT_AUTO_GEN (near P222) short these two points and plug in the tv, see if you have test patters on screen, If not, unplug tv, disconnect P231 from main board, short the test points and plug in the tv
A buzzing noise from the y-sus board is normal

[maces]

Re: LG 60PH6608 YSUS repair

Thank you for the usful tip. The test image was good.
Then I found the error by looking at the mainboard. There was a bad connection between power supply board and mainboard - the connector was not plugged in correctly. Now the TV is running since two hours.

But now, I have the issue that the image is "noisy".
Theres a kind of red noise I can see when the screen is white. It is not evenly distributed on the image. I tried to make a short video:

https://www.dropbox.com/s/6fdn0a64u5...83337.mp4?dl=0

[R_J]

Re: LG 60PH6608 YSUS repair

Make sure the voltages for VS and VA are correct, Also check the VSC voltage on the Ysus board, it is measured across the two points marked -VSC+, the correct values for the voltage are on a sticker on the panel. If the voltages are correct, or very close, you can try increasing or decreasing the VS voltage ay a few volts to see if the image gets better, Then Mark the positions of the SETUP and SETDN controls and slightly adjust each one while watching the picture and adjust for the lest amount of specks in the white and black areas, it will likely never go away completely. It's best to do the adjustments after the panel as been on for a while.
Many of these LG plasmas usually required a software update to the control board to fix this issue, also this can happen as the panel ages.

You can also check and/or re-solder the connections on the large coils on the Y-sus and z-sus boards, then make sure that all the ground screws are in place and fairly tight.

[maces]

Re: LG 60PH6608 YSUS repair

VS and VA are correct.
VS is measured with 203V and VA with 55V, as noted on a sticker on the panel.
For VSC I cannot find a reference. The measured voltage across the two points is 149V. Is this a correct value for VSC?

[maces]

Re: LG 60PH6608 YSUS repair

I tried to increase the VS voltage up to 208V. This causes no positive effect, so I readjusted it to 203V.

The only positive effect I can see is if I turn the SETUP potentiometer complete to the left. Then the noise is nearly complete gone. The white gets a little "blue-gray" but it is better then the noise.
But I have doubts if I can leave the poti complete to the left in contineus operation.

[R_J]

Re: LG 60PH6608 YSUS repair

below the Vs and Va voltages on the label it usually lists the other voltages like VSC
Post a picture of the label. I believe the VSC voltage is the third one listed

It might read N.A./ -180 / 150/ N.A./ 105 in this case 150 is the VSC.

Normally the Setup and Setdn are adjusted using a scope and adjusting for a proper waveform

You won't get it perfect so adjust it for minimum speckle and be done