LG Plasma TV Model 50PN4500-TA

[angelos]

Hi Guys, I desperately need your advice on this set.
When pressing standby to "ON" then the Panel has a pre charge flash and further no image. The audio works 100%. I have the TV plugged into HDMI input.
I measured all the main board voltages and they are all correct according to service manual. I then went to the logic board and put a wire on the "Auto" to generate
its own test patterns. This works, telling me that the plasma panels are ok. After removing the jumper we go to having a black image.
I cleaned the ribbon from the main to the logic board, it made no difference.
I have used a scope to observe the signals going to the logic board and they are there. They are weak little voltages of less than a volt. But I cannot say if they are correct because the service manual; has no oscillogram images showing what to expect.
On the logic board there is 3.3V and 1.2V present, the logic chip get warm but not hot to burn you.
If the logic chip can self generate an image using the "auto jumper" can there still be an issue with it?
Or is my main board faulty.

Awaiting humbly your response
Angelos

[angelos]

Anybody there have experience or can advise me to what to look for?

[lotas]

The voltage on the motherboard is 3.3v and 1.2v, which is not enough; there should be more on each converter with its own voltage...

[lotas]

And also, the TV has been in a damp room or in the rain, the tuner on your motherboard has rusted, and the resistors on the logic have rotted, you don't know what's going on under the chip.

[angelos]

The voltage on the motherboard is 3.3v and 1.2v, which is not enough; there should be more on each converter with its own voltage...

Hi Lotas, thanks for your reply. I have added board voltages for you to check but according to the service manual they are all 100%
I think you are right, moisture has probably corroded the BGA solder under the logic board. Unless you have something else to add I think i am stuck. No logic board available.
Thanks for your help.
Angelos

[lotas]

Wash the Logic board in a soapy solution and carefully, without fanaticism, clean the places where there was moisture with a toothbrush, then rinse thoroughly with running water, dry the board with a hairdryer and inspect the board under a magnifying glass for suspicious places, measure the resistance of the resistors - they should all be the same in resistance.
If you have an ultrasonic bath, that will be good.