Troubleshooting my LG plasma TV - no picture display

In summary, the LG 42PQ30R plasma TV has no display. The power supply is ok, and the Ysus board is also ok. However, there is a doubtful MOSFET on the Ysus board and the floating voltage at P207 is not checked. The next step is to check the video signal, if that is ok, and then trace back towards the antenna until you find a signal.
  • #1
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 )

Screen Shot 2020-09-08 at 8.58.47 PM.png



  • 42pq30r manual.pdf
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  • #2
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!
  • #3
Tom.G said:
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.

Tom.G said:
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.

Tom.G said:
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.
  • #4
brainbaby said:
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 :smile:
snow on a TV/hiss on a radio is essentially random noise
  • #5
I am assuming that you have inspected for bulged caps and replaced any you found.
  • #6
Integral said:
I am assuming that you have inspected for bulged caps and replaced any you found.
did that, all seems good at least physically.
  • #7
davenn said:
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.

1. Why is my LG plasma TV not displaying any picture?

There could be several reasons for this issue. It could be a problem with the TV's power supply, a faulty cable connection, or a malfunctioning display panel. It is best to troubleshoot each of these possibilities to determine the exact cause.

2. How do I troubleshoot the power supply of my LG plasma TV?

First, check if the TV is properly plugged into a working power outlet. If it is, try unplugging it and plugging it back in after a few minutes. If the TV still does not turn on, there could be an issue with the power supply board, which may need to be replaced by a professional.

3. What should I do if the cable connection seems to be the issue?

Make sure all cables are properly connected and not damaged. If using an HDMI cable, try using a different one. If using a cable box, try connecting it directly to the TV to see if the issue is with the box. If none of these solutions work, the issue may be with the TV's input ports, which may need to be repaired or replaced.

4. Can I fix a malfunctioning display panel on my own?

It is not recommended to attempt to fix a display panel on your own. It is a complex and delicate component that requires professional expertise. Attempting to fix it yourself may cause further damage to the TV.

5. What should I do if none of the above solutions work?

If troubleshooting the power supply, cable connection, and display panel do not resolve the issue, it is best to contact LG customer support or a professional TV repair service. They will be able to diagnose the problem and provide the necessary repairs.