Hello all, this thread covers the repair and diagnoses of this this 50" Lg plasma model 50PS3000. This particular tv had an issue where the Vs & Va voltages that drive the sustain-boards was dropping out and come up at random, this issue is affected by the temperature of the tv and is intermittent which is normally alot harder to diagnose where as if its a solid fault like no power at all it is alot easier to diagnose.
Firstly I suspected the sustain boards as the most common issue with this particular set is faulty Zsus and Ysus however unplugging them made no difference to the sets behaviour it was still loosing the Vs & Va. So from this I knew that the Psu or Mainboard is at fault and that the sustain boards are ok.
Reading up I was able to find that the control board can cause the issue described and upon unplugging that the voltages never faulted out however it was not the control board. I replaced all the 100uf 25v caps on the control board plugged it in tv worked then faulted out again.
Now normally I would check the voltages that are listed on the little chart on the to the connector on the Psu I never did this. All the voltages are fine however the "Vs on" signal that the Mainboard generates which normally is 3.3v which tells the Psu to run the Vs & Va this power on command is coming and going at random also all the other voltages are perfect. So from this I was able to determine that the Psu is probably ok but is being told to run then turn off run then turn off the Vs & Va
From this I was able to determine that the Mainboard is actually faulty here. Now after heating the Mainboard with a hair drier it worked then letting it cool it failed. Also by tapping it lightly with my hand and flexing it failed then worked bring up the Vs on and loosing it depending on how I treated it.
I ended up replacing the Mainboard for £20 off ebay and the set now works. Now I noticed "Pb free soldering" aka lead free solder and that when the set worked the cpu heatsink got VERY hot, so this failure is probably due to heat and more crappy lead free solder failing and cracking, then when I flexed the Mainboard it re-bonded it and sorted it then when it cooled it cracked and caused the issue. Charged £110 for repair and another happy customer and another tv saved
Link to the video of the diagnoses and repair:
https://m.youtube.com/watch?v=66SeSEFVc-8
Firstly I suspected the sustain boards as the most common issue with this particular set is faulty Zsus and Ysus however unplugging them made no difference to the sets behaviour it was still loosing the Vs & Va. So from this I knew that the Psu or Mainboard is at fault and that the sustain boards are ok.
Reading up I was able to find that the control board can cause the issue described and upon unplugging that the voltages never faulted out however it was not the control board. I replaced all the 100uf 25v caps on the control board plugged it in tv worked then faulted out again.
Now normally I would check the voltages that are listed on the little chart on the to the connector on the Psu I never did this. All the voltages are fine however the "Vs on" signal that the Mainboard generates which normally is 3.3v which tells the Psu to run the Vs & Va this power on command is coming and going at random also all the other voltages are perfect. So from this I was able to determine that the Psu is probably ok but is being told to run then turn off run then turn off the Vs & Va
From this I was able to determine that the Mainboard is actually faulty here. Now after heating the Mainboard with a hair drier it worked then letting it cool it failed. Also by tapping it lightly with my hand and flexing it failed then worked bring up the Vs on and loosing it depending on how I treated it.
I ended up replacing the Mainboard for £20 off ebay and the set now works. Now I noticed "Pb free soldering" aka lead free solder and that when the set worked the cpu heatsink got VERY hot, so this failure is probably due to heat and more crappy lead free solder failing and cracking, then when I flexed the Mainboard it re-bonded it and sorted it then when it cooled it cracked and caused the issue. Charged £110 for repair and another happy customer and another tv saved
Link to the video of the diagnoses and repair:
https://m.youtube.com/watch?v=66SeSEFVc-8
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