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-   -   Short circuit on Y Buffer board, or bad panel ? (https://www.badcaps.net/forum/showthread.php?t=69707)

guix 05-18-2018 11:50 AM

Short circuit on Y Buffer board, or bad panel ?
 
4 Attachment(s)
Hello,

Someone gave me a plasma TV Samsung PS50C530, which didn't turn on. It's the first plasma TV that I open and try to repair. I have repaired some LED TV but it was mostly simple things like replacing backlight or capacitors.

I found shorted components, and an exploded disk capacitor, on the Y Main board, so I bought an Y Main board on ebay, but when I installed it in the TV and tried to turn it on, it blew up instantly. All I saw was a few random white pixels on the display, then I heard "pak" from an unknown place (can't see any damaged component on any board) and now the "new" Y Main board shows the same problem as the old one, with shorts on multiple components. I also checked Va and Vs (with Y Main board disconnected so the SMPS could start) and those two voltages are good. I know the TV sound is working because I connected a HDMI cable, turned the TV on (still without Y Main) and could blindly select the HDMI input withthe remote, and heard the sound from it. Also the LED on the Logic Board flash at 1Hz.

So I think the problem might be, either a bad panel, or a bad Y Buffer board. I did the Y buffer test as shown in youtube videos:
https://www.badcaps.net/forum/attach...1&d=1526663103
But couldn't find any shorts (I tried with all other pins on the white connectors too).


However I think I've found that all "big" diodes and resistors are shorted:
https://www.badcaps.net/forum/attach...1&d=1526663211
My multimeter beep when I touch the two side of diodes like the one in this picture. This is bad and shouldn't happen, right !?? I tried to remove the diodes but the shorts are still here after removal. When I measure resistance across these resistors I always get around 2 ohms. As you may see I've removed the hot glue from a chip but not sure what to test here because I don't find the datasheet for that chip (Panasonic AN16489A).

Do you think that this Y Buffer board is bad and caused both Y Main boards failures ? And may it have originated from a bad panel ? I don't see any damage on the panel itself, however the TV bezel is damaged like if it felt on concrete or gravel:
https://www.badcaps.net/forum/attach...1&d=1526664867

I'm wondering about buying a new Y Buffer, and again a new Y Main (and also X Main maybe, however I can't find any shorts on that board, but does that mean that it's good?). But before I do so, is there anyway to check if the panel itself is good and won't blow up the new components instantly?

Here is a picture of the whole Y buffer board:
https://www.badcaps.net/forum/attach...1&d=1526663211


What do you think about it? Thanks!

moateez 05-18-2018 04:38 PM

Re: Short circuit on Y Buffer board, or bad panel ?
 
The short in diodes is normaly because the didodes is conect etwen resestor 220ohm

Give me picture for the backbsid of carte y you wil find transistor. Igbt in short you replace theme

guix 05-18-2018 06:57 PM

Re: Short circuit on Y Buffer board, or bad panel ?
 
5 Attachment(s)
Hello,

So you are saying it is normal to have shorts here, and so this Y Buffer board looks fine ? As I'm still new to electronic, can you explain the purpose of this diode and those 22 ohm resistors, which looks totally useless to me since they are basically shorted and electrons won't bother to go through them ?

And what could have caused the two Y Main boards to fail then, if the Y buffer is ok and Va and Vs are fine too..? Could it be a problem with X Main board, on which I have not find any shorts or exploded components ?

I have removed all components that were shorted on the original Y Main board, so there is no short anymore on that board, but do I just replace these components and the capacitor that exploded, and the board should work again ?
https://www.badcaps.net/forum/attach...1&d=1526690654
All components removed in the picture above need to be replaced, except the four big capacitors (I needed to remove them to remove the screws on the heatsink), and the big diode which tested fine as shown in this picture:
https://www.badcaps.net/forum/attach...1&d=1526690683

And sorry that I forgot to put the TV model in title, but I can't edit it...

moateez 05-19-2018 02:16 AM

Re: Short circuit on Y Buffer board, or bad panel ?
 
But you nedd to replace IGBt transistor with Original Part and it will go ok

tom66 05-19-2018 03:50 AM

Re: Short circuit on Y Buffer board, or bad panel ?
 
If a Y-buffer board fails it will short between VSCH and VFG/VSC on the Y-board.
The VFG is the large "ground plane" on the board BUT it is not the same as ground, it is a floating ground.
VSCH is 150V above VFG.
It is rare though not impossible for a Y-buffer board to damage the Y-main. It is far more likely for the reverse to occur.


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