Troubleshooting my LG plasma TV - no picture display

[brainbaby]

Hi friends,

Let me brief, long story short..
I am working on an LG plasma TV model 42PQ30R.
The fault is no display.
The tv is turning on, the blue led is working, however there is no standby (red light), tv automatically going in run mode (i.e blue led)
Note: sometimes gets off automatically but it happened only once or twice.

I began my troubleshooting with the power supply, all fuse ok.
power supply ok, getting the required panel voltages (Vs and Va) at power supply outputs.

My next step was to check the Ysus board.
Ysus P201 to SMPS P812 connector is OK.
Ysus P209 to left X drive --ok
checked the MOSFETs, IGBTs, all ok except a few, IRGP 4086, IRFP 4332, K3667 (2), but cannot confirm as they were tested onboard, not standalone.
Ysus P206 to Z sus ---doubtful, reason -fluctuating voltage received at Er com and VS pins which should be as per panel label i.e 94.9 and 193 V respectively.
Not checked the floating voltages at P207 (Ysus to Y drive), as I haven't ascertained pins where and how to measure floating voltages, I don't have any isolation transformer.

My question is what seems to be the fault , am I going in the right direction, what should be my next step?

additional info- the fault started with the TV displaying coloured snow in picture and then by the time it went pitch black .
I am taking help from the LG training manual (please refer attachment )

Regards!

 

[Tom.G]

Also check if the Setup function is available and try the HDMI input. If those work, then proceed as below.

Colored snow is circuit and/or atmospheric noise. Many (all?) digital TVs automatically blank the screen with no incoming signal. Try checking for a video signal present. Then trace back towards the antenna until you find a signal.

Good Luck!
Tom

 

[brainbaby]

Setup function is available

no step up function is available since there is no menu display, unable to do so.. It seems like the panel display is not starting, how ever all panel boards are powered up.

Colored snow is circuit and/or atmospheric noise.

exactly, snow happens due to interference among the tv channels, and the fault corresponds to the RF section in old CRT tvs but here since now there is no display, it seems to be the defect of the Ysus board. I have read somewhere that the Y sus gives the drive signal needed to project the display on to the screen.

TVs automatically blank the screen with no incoming signal.

my tv doesn't do this rather with no incoming signal it just resembles to the CRT tvs.

 

[davenn]

snow happens due to interference among the tv channels

no, read again what TomG said

Even if there was a single channel transmitter there would still be snow / hiss on unused channels
snow on a TV/hiss on a radio is essentially random noise

 

[Integral]

I am assuming that you have inspected for bulged caps and replaced any you found.

 

[brainbaby]

I am assuming that you have inspected for bulged caps and replaced any you found.

did that, all seems good at least physically.

 

[brainbaby]

no, read again what TomG said

I agree with you.., but now the problem isn't snow. Presently, the display panel is not powering up..which is somewhat related to the Y sustain board (but not necessary). If in future if the display does power up, and still the snow persist then probably I will look in RF control board.