Hmm, I picked up this LG 50PA650T full HD 1080p 50" plasma. £50 bargain, so from never touching a single modern design LG plasma in a week, I've got two!
Turning on, got Vs/Va, but -Vy and Vsc all over the place, no image on panel. Uses a PDP50R4 panel, which is a fairly significant change from PDP50R3 (the panel Vsc/-Vy is offset by some third, unknown voltage, which is very odd; will have to investigate this later. Had thought practically all R&D had stopped at LG PDP.)
Remove top buffer, got picture on bottom half... good Vsc/-Vy too. Image is a little fuzzy but this is probably due to poor ERC (half panel connected = half capacitance so panel not properly sustained.)
Top most buffer chip is shorted. Now I remember this thread from freakaftr8.
https://www.badcaps.net/forum/showth...light=50pa5500
He had a bad top buffer and a ribbon rubbing against the panel shorting the new buffer out.
Here, I'm a little worried, because I can see a dimple in my top ribbon, not present in any other ribbons. However, I cannot find ANY shorts between Z-sus out and this ribbon or between this ribbon on chassis. Not even high ohm. All >66 Megohm on my meter.
So, what could have happened?
1. Maybe it's a random buffer board failure, this is a fairly new TV though, so it is a little unexpected. There are no heatsinks on the buffer ICs like in older LG panels.
2. Maybe the ribbon is rubbing against the frame like in freak's case, but only when the panel warms up or if the TV is flexed slightly (side plastic is a little scratched and two screw mounts are damaged.) There are no cracks in the panel at all and bottom half will sustain image OK. AND, here's the important bit, when I check the buffer chip (top buffer IC) with my meter, the part which is shorted seems to correspond to this area of the panel. However, I don't believe that not addressing each line will blow a buffer as freak states. Case in point, unplug a ribbon, and it'll work for hours with it out. I did it accidentally for 10 minutes with this TV and no harm to the bottom board. So it must be a short that kills it.
3. Maybe we have a panel failure like in PZ70 Panasonic though I can't see any blown pixels or shorts in ribbons apparently this only shows up after the panel gets warm.
Potential fix:
If it's (1) just replace the buffer and enjoy; (2) replace buffer and isolate the ribbon with some insulator - as Freak said it might be shorting? or (3) scrap the TV for parts - hopefully not as this is quite a nice TV!
Turning on, got Vs/Va, but -Vy and Vsc all over the place, no image on panel. Uses a PDP50R4 panel, which is a fairly significant change from PDP50R3 (the panel Vsc/-Vy is offset by some third, unknown voltage, which is very odd; will have to investigate this later. Had thought practically all R&D had stopped at LG PDP.)
Remove top buffer, got picture on bottom half... good Vsc/-Vy too. Image is a little fuzzy but this is probably due to poor ERC (half panel connected = half capacitance so panel not properly sustained.)
Top most buffer chip is shorted. Now I remember this thread from freakaftr8.
https://www.badcaps.net/forum/showth...light=50pa5500
He had a bad top buffer and a ribbon rubbing against the panel shorting the new buffer out.
Here, I'm a little worried, because I can see a dimple in my top ribbon, not present in any other ribbons. However, I cannot find ANY shorts between Z-sus out and this ribbon or between this ribbon on chassis. Not even high ohm. All >66 Megohm on my meter.
So, what could have happened?
1. Maybe it's a random buffer board failure, this is a fairly new TV though, so it is a little unexpected. There are no heatsinks on the buffer ICs like in older LG panels.
2. Maybe the ribbon is rubbing against the frame like in freak's case, but only when the panel warms up or if the TV is flexed slightly (side plastic is a little scratched and two screw mounts are damaged.) There are no cracks in the panel at all and bottom half will sustain image OK. AND, here's the important bit, when I check the buffer chip (top buffer IC) with my meter, the part which is shorted seems to correspond to this area of the panel. However, I don't believe that not addressing each line will blow a buffer as freak states. Case in point, unplug a ribbon, and it'll work for hours with it out. I did it accidentally for 10 minutes with this TV and no harm to the bottom board. So it must be a short that kills it.
3. Maybe we have a panel failure like in PZ70 Panasonic though I can't see any blown pixels or shorts in ribbons apparently this only shows up after the panel gets warm.
Potential fix:
If it's (1) just replace the buffer and enjoy; (2) replace buffer and isolate the ribbon with some insulator - as Freak said it might be shorting? or (3) scrap the TV for parts - hopefully not as this is quite a nice TV!
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