Lg 50pm6700 no picture but sound

[Rickthegreen]

Hi guys ! long time lurker here

So it is an LG 50pm6700, chassis pdp50r40000

No picture at all but sound on hdmi source by going blind at selecting an input

Vs = 206v
va = 55v

5v is good also the 17 volts

Heat sink on boths driver boards are warm
fuse on the 16 volts on one driver board is ok
the other one on the 55v supply is ok also

vzb = 150 v

vsc and vy are all over the place can't get a stable reading on the resistor test points ??

Where to go from here ? can't find a schematic even on tom66 site

Thanks,
Rick

[tom66]

Re: Lg 50pm6700 no picture but sound

Check the -Vy, Vsc and Vzbias voltages on the sustain boards. They should be clearly marked.

[Rickthegreen]

Re: Lg 50pm6700 no picture but sound

Hi tom66, thanks for reply

Like i said vsc and vy are all over the place, should they be stable DC voltage ?

I measured them where across some 1 watt resistors where they were marked.

the voltages were varying like crazy, i was not able to get a clear reading, both of them.

[Hamie]

Re: Lg 50pm6700 no picture but sound

Probably bad buffer boards.
Unplug the buffers and check the -vy, vsc voltages again.
If they now match the panel then suspect bad buffers, and check for shorts.

[Rickthegreen]

Re: Lg 50pm6700 no picture but sound

Hi gain !

There is 1 chip blown on the buffer board, i didn't see it at first glance, i smelled it that's what caught my attention .
My question is IF i can find the board, is there a chance that the plasma itself has a problem that will blew-up the board again ?

Thanks,
Rick

[ivpavel]

Re: Lg 50pm6700 no picture but sound

I have the same tv and same problem except the buffer chips look fine. Any other thoughts on what might be wrong with it? If not I guess I will be ordering some chips to see if I can replace them because the board would cost as much as I would sell the tv for.

[ReeceyBurger123]

Re: Lg 50pm6700 no picture but sound

Test buffer before guessing, all im saying.

[ivpavel]

Re: Lg 50pm6700 no picture but sound

How do I test the buffer?

[qweasdzxc]

Re: Lg 50pm6700 no picture but sound

How do I test the buffer?

You can test the buffer board using a multimeter. Take out the cables that connect the buffer board to the panel. Then, put your multimeter to the diode test mode (it should buzz when the positive and negative ends touch). You should then put the negative end on a screw and move the positive endalong the connectors on the buffer board. If you get a buzzing noise, one of the chips on the buffer board is short circuited. If you aren't getting a buzzing noise, it is most likely working fine.

[ivpavel]

Re: Lg 50pm6700 no picture but sound

Thanks I will try that

[qweasdzxc]

Re: Lg 50pm6700 no picture but sound

You can test the buffer board using a multimeter. Take out the cables that connect the buffer board to the panel. Then, put your multimeter to the diode test mode (it should buzz when the positive and negative ends touch). You should then put the negative end on a screw and move the positive endalong the connectors on the buffer board. If you get a buzzing noise, one of the chips on the buffer board is short circuited. If you aren't getting a buzzing noise, it is most likely working fine.

It doesn't matter which end you put in which place.

[ivpavel]

Re: Lg 50pm6700 no picture but sound

Got that sucker it was one of the ICs on the lower part of the buffer board