Troubleshooting my LG plasma TV - no picture display

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Discussion Overview

The discussion revolves around troubleshooting an LG plasma TV model 42PQ30R that is experiencing a no display issue. Participants explore potential causes and solutions, focusing on the power supply, Ysus board, and related components. The conversation includes technical details about voltage readings and circuit behavior, as well as the implications of previous symptoms like colored snow on the screen.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Exploratory

Main Points Raised

  • One participant describes the initial troubleshooting steps taken, including checking the power supply and Ysus board, and notes fluctuating voltages at certain pins.
  • Another participant suggests checking the Setup function and HDMI input, indicating that colored snow may be due to circuit noise and that the TV could be blanking the screen due to a lack of signal.
  • A participant clarifies that the Setup function is unavailable due to the absence of a menu display, suggesting that the panel display is not starting despite power to the panel boards.
  • Discussion includes the interpretation of colored snow as interference, with some participants debating its relevance to the current issue of no display.
  • There is a mention of inspecting for bulged capacitors, with one participant confirming that they have done so and found no issues physically.
  • Another participant emphasizes that the current problem is not related to snow but rather the display panel not powering up, linking it to potential issues with the Y sustain board.

Areas of Agreement / Disagreement

Participants express differing views on the cause of the no display issue, with some focusing on the Ysus board while others discuss the implications of colored snow and signal interference. There is no consensus on the exact fault or next steps.

Contextual Notes

Participants mention specific voltage readings and components but do not resolve the uncertainties regarding the measurements or the implications of the observed symptoms. The discussion reflects a range of hypotheses without definitive conclusions.

brainbaby
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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


Regards!
 

Attachments

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