TV LG 50PA4500 Plasma : bad image noisy

[Delired73]

Hello everyone,

I have an issue and didn't find any solution by myself or on every forum about my LG plasma TV 50PA4500.

Originaly the TV stopped to work and didn't want to turn ON again.

After visual inspection, few transistors were broken, I tried to change them but some burned again, so I ordered on full new board. So, I changed the Yboard which was burned by a new one

It now turns ON and the image and sound are present. But the image is very noisy and only visible when the room is in the dark.

I check Vs and Va voltages which are perfects.

I join 2 pictures, one took with the room at ambiant light (the image is almost invisible) and one with the room put in the dark (The image can be well see but the colors are very bad).

[R_J]

Re: TV LG 50PA4500 Plasma : bad image noisy

Check and adjust Vy You may need to adjust the Ramp_up & Ramp_dn slightly, mark the controls with a felt marker before adjusting so the can be returned to there original positions if needed. Adjust these two controls while observing the screen, you should not need to move them very far to see a change.

[Delired73]

Re: TV LG 50PA4500 Plasma : bad image noisy

Hello R_J,

Thank you for your answer. Ramp_up & Ramp_dn signals were at their best value but indeed Vy value was wrong. Unfortunately even by moving it at his maximum, the image is going better but never good enough, far from that.

I will resend the Yboard just reconditioned to have a new one and will keep you in tuch.

Thank you again !

[Delired73]

Re: TV LG 50PA4500 Plasma : bad image noisy

Hello,

Finally after reflexion, I found how to measure Vy and Vsc and Vzb, everything seems ok. So I don't have any idea of what check now to find the origin of these very dark colors.

[Biruslapio]

Re: TV LG 50PA4500 Plasma : bad image noisy

I've repaired Y and Z boards for this TV, there might be some resistors that are open on Y-SUS or Z-SUS, Usually 2.2 OHMs 2W and/or 2R2 SMD resistors next to 155E optocouplers, 10 or 15 OHMs at transistors gate pins.

This model also has Y-buffer failures, check if all the horizontal pixel lines on TV are properly working, but it would shut down if that was the problem.