LG 60PM6700 no picture no sound

[Mikeyjohnson]

Hey guys im working on a LG plasma and i tested the vs and va on both the Ysus and Zsus boards. I have correct voltages. But when i power on the tv the tv clicks like normal stand by light goes off and the panel lights up then darkens down a little bit. Did some research on line on a website and it stated to disconnect the Ysus board and see if the tv turns on. Which it does, but no power to the screen. They states if the tv still turns on still with no picture that would be the problem. Any suggestions?

I can post pictures if needed.

[tvtimmy]

Re: LG 60PM6700 no picture no sound

Go to the logic control board in the middle of the set. Flip up the brown latch on P231 and remove the flat ribbon. Put a paper clip in the 2 holes marked EXT_AUTO_GEN. Power on the tv and check if the test screens come on. If they do, the mainboard is bad.

[Mikeyjohnson]

Re: LG 60PM6700 no picture no sound

Do i put 2 different paper clips or do i loop it?

[tvtimmy]

Re: LG 60PM6700 no picture no sound

Loop it.

[Mikeyjohnson]

Re: LG 60PM6700 no picture no sound

Perfect! Thank you. Just did it and the test pattern came on. Learn something new everyday. Does that trick only work with LG and this model or all plasma's?

[tvtimmy]

Re: LG 60PM6700 no picture no sound

If you get a screen glow, test the tv this way. It works on all LG plasmas. It also works on Samsung plasmas, just have to short pins 3 & 4.

[Mikeyjohnson]

Re: LG 60PM6700 no picture no sound

Got it. And those are the pins thats on the main?

[Mikeyjohnson]

Re: LG 60PM6700 no picture no sound

Sorry for all the questions learning aint a bad thing. Thanks again.

[tvtimmy]

Re: LG 60PM6700 no picture no sound

No. You are disconnecting the mainboard from sending info to the control board. This tests the logic/control board. Samsung plasmas have the 4 pins on the logic/control boards. You use a jumper from an old dvd rom or hardrive(master,slave selector) and put it on pins 3 and 4.

[Mikeyjohnson]

Re: LG 60PM6700 no picture no sound

Got it. Thank you so much for the info.

[Hamie]

Re: LG 60PM6700 no picture no sound

Probably caused by bad solder joints under the xd engine.
Give it a reflow and see if it comes back to life.

[tvtimmy]

Re: LG 60PM6700 no picture no sound

Yep. You got nothing to loose. I use a Wagner heat gun on LOW for about 45 seconds.
Fixed many LG tvs this way.

[tnbugman]

Re: LG 60PM6700 no picture no sound

An old but related thread, I've got an LG 60PM6700UB that is driving me crazy. Picture and sound are great, but TV turns off after about 20 minutes. If you turn it back on too quickly, there is sound but no picture. If you wait a while, picture and sound are fine, but it turns itself off again after 20 minutes.
I have already replaced EVERY BOARD except the small logic board without affecting this turning off problem.
Q557 and Q556 on the short black metal heat sink of the Y-SUSTAIN board get very hot, and I think this is why the logic board turns off the TV. I have replaced both the upper and lower Y buffer boards as well, but no luck.
The green led on the logic board starts out with a "long-short long-short" flash, but then it changes to a "long-short long-long" flash just before the TV turns itself off.

Has anybody got any ideas for anything else I could try? I'm at my wits end on this one ...

Thanks in advance for any advice!

[Unspun01]

Re: LG 60PM6700 no picture no sound

I have already replaced EVERY BOARD except the small logic board without affecting this turning off problem.
Q557 and Q556 on the short black metal heat sink of the Y-SUSTAIN board get very hot, and I think this is why the logic board turns off the TV.

I think you found your issue - the logic board.

I was just involved in another thread for an LG 60PS60 where the logic board had bad electrolytic capacitors and caused the IGBTs on the YSUS board to conduct longer, and therefore run hot and fail. The fix on the LG 60PS60 was to replace the bad surface mount electrolytic capacitors (or the logic board)...

https://www.badcaps.net/forum/showth...t=72695&page=2

However, on your TV logic board, there are no electrolytic capacitors on the logic board so it could be bad BGA solder connections or something else.

You may try replacing the logic board...

Fortunately, your YSUS is not damaged. Unfortunately, replacing the logic board is the last board instead of the first board in your repair.

[tnbugman]

Re: LG 60PM6700 no picture no sound

Thanks very much for this quick and knowledgeable reply.

I will replace with a new logic board ASAP, and will report back again.

Stay tuned!

[tnbugman]

Re: LG 60PM6700 no picture no sound

well, I just replaced the small logic board, with no change in the symptom. The set still switches itself off after 20 minutes, after the short black metal heat sink gets so hot that I cannot touch it. The green led on the logic board switches from blinking "long-short long-short" to "long-short long-long" flashes right before it switches off.
I've now replaced every board in this set, including upper and lower y buffers (not z buffers though). Can the display panel itself be bad somehow? Picture and sound look perfect. Any further suggestions? I am stumped and at an impasse ... Thanks.

[tvtimmy]

Re: LG 60PM6700 no picture no sound

I would look at the bottom of the power supply and redo all the solder joints on everything mounted to a heatsink. Also redo all the transformer solder joints. Maybe check the poly capacitor at C802.

[tnbugman]

Re: LG 60PM6700 no picture no sound

Thanks for the advice. I have replaced the entire power supply board already though, no change. To be clear, one of the black metal heat sinks on the ysus board is getting very hot. After 20 min of good picture and sound, the TV turns itself off.
I have also replaced the ysus board (first), and also the upper and lower y buffer boards (second). No change in the symptom.
Starting to wonder if the old y buffer boards blew out my new ysus board.

Any advice greatly appreciated ... Bill H.

[maki]

Re: LG 60PM6700 no picture no sound

Thanks for the advice. I have replaced the entire power supply board already though, no change. To be clear, one of the black metal heat sinks on the ysus board is getting very hot. After 20 min of good picture and sound, the TV turns itself off.
I have also replaced the ysus board (first), and also the upper and lower y buffer boards (second). No change in the symptom.
Starting to wonder if the old y buffer boards blew out my new ysus board.

Any advice greatly appreciated ... Bill H.

This sounds like a power supply issue.
These TVs are known foe their PS faults.
Is it possible that the replaced PS board has also a fault?
I assume you got it as used, right?

[Unspun01]

Re: LG 60PM6700 no picture no sound

Thanks for the advice. I have replaced the entire power supply board already though, no change.

When you replaced the power supply, did you test the Va and Vs voltages to see if their output matches the voltages necessary as printed on the panel sticker?

There are two adjustment potentiometers located near connector P811

Va is adjustable via potentiometer VR502
Vs is adjustable via potentiometer VR901

If your Va or Vs are too high, or too low, you could be affecting drive voltages on sustain boards which run hot and lead to shut down.

What are the required Va and Vs voltages as printed on the panel sticker and what are you actually measuring from the power supply test points for Va and Vs?

The test points are identified as VA TP and VS TP on the PCB (and can be measured by probing the adjacent jumper with reference to ground).