Morning All!
I found two failed Fet's on the Y-Buffer boards, removed them and the display starts working normally.....HUH? How does that work? Details below.
Was just given my first plasma project TV. Not sure that's a good things with everything I've read so far about this particular model….
The unit would power on with a dark snowy background and audio. If I pressed the input button vertical blocks would present from top to bottom varying from 1/4" to 2" in width. Pressing the input button again would move and change this pattern to a different section of the screen. There was no visible OSD menu. I'm calling this corruption of the OSD since the faint background didn't change. Wish I would have taken pics, sorry about that.
Anyways….
After a lot of researching and studying I followed the advice posted on another thread to unplug the lower buffer board (YDRV BOT) and power on.
Sure enough, the upper half of the screen started working. I pulled both filter boards and identified two shorted mosfets on the lower board.
I then started to search for known causes of the fet's to short and started thinking. Since I am planning to replace all of the fets on both boreds I had an idea. Remove the two failed one's(the two that are back to back) remove two good ones from the upper board and install on the lower board for troubleshooting.
I re-installed both boards and hooked everything up as it normally should be. All mosfets on lower board now tested good and there are two missing mosfets on upper board.
I powered it on, and could have S&$# a bright white snowy pictured appeared with audio just like it should on the entire screen. I then tried changing inputs and the OSD displayed as normal. I attached my laptop to pc input and it displays on the entire screen. I wanted to remove power to the unit as quickly as possibly until I understand what's going on so I didn't check closely for picture quality.
So, I have a few questions on this project.
1) Why/how is it possible to have a picture on the entire screen with 2 missing mosfets?
2) I have the Toshiba service manual for this set; does anyone know where I can find a Toshiba Training Manual specifically for this chassis? OR does anyone know of an equivalent LG training/service manual that I can trust. Mostly looking for TP and Voltages at this time. After reviewing some of the other training manuals I feel I would learn a LOT more about Plasmas then I currently do.
3) I've read the horror stories about the IPM'S going out. I have a noticeable oscillating sound coming from one or both of mine. Is that normal or a sign that they are failing and possibly the cause of the blown fets?
4) I read on another post the recommendation of using FDB52N20 as a heavy duty replacement to the FQB46N15 that are currently installed. Any thoughts? At this point I am planning on ordering the heavy duty ones.
5) Are there any other parts I should consider replacing, in general and specifically related to the shorted fets, since I have to put an order in?
6) Was going to give this unit to my dad to replace his 30yo, non-HD, tube set. Am I asking for a lot of headaches and be better off selling it instead for something newer?
That's all my frozen brain can think of at the moment, have spent way to much time on this unit…..because I love every minute of the adventure of learning something new! Just love this stuff.
You guy's ROCK! Thank you for any and all thoughts/advice/input.
Randy
I found two failed Fet's on the Y-Buffer boards, removed them and the display starts working normally.....HUH? How does that work? Details below.
Was just given my first plasma project TV. Not sure that's a good things with everything I've read so far about this particular model….
The unit would power on with a dark snowy background and audio. If I pressed the input button vertical blocks would present from top to bottom varying from 1/4" to 2" in width. Pressing the input button again would move and change this pattern to a different section of the screen. There was no visible OSD menu. I'm calling this corruption of the OSD since the faint background didn't change. Wish I would have taken pics, sorry about that.
Anyways….
After a lot of researching and studying I followed the advice posted on another thread to unplug the lower buffer board (YDRV BOT) and power on.
Sure enough, the upper half of the screen started working. I pulled both filter boards and identified two shorted mosfets on the lower board.
I then started to search for known causes of the fet's to short and started thinking. Since I am planning to replace all of the fets on both boreds I had an idea. Remove the two failed one's(the two that are back to back) remove two good ones from the upper board and install on the lower board for troubleshooting.
I re-installed both boards and hooked everything up as it normally should be. All mosfets on lower board now tested good and there are two missing mosfets on upper board.
I powered it on, and could have S&$# a bright white snowy pictured appeared with audio just like it should on the entire screen. I then tried changing inputs and the OSD displayed as normal. I attached my laptop to pc input and it displays on the entire screen. I wanted to remove power to the unit as quickly as possibly until I understand what's going on so I didn't check closely for picture quality.
So, I have a few questions on this project.
1) Why/how is it possible to have a picture on the entire screen with 2 missing mosfets?
2) I have the Toshiba service manual for this set; does anyone know where I can find a Toshiba Training Manual specifically for this chassis? OR does anyone know of an equivalent LG training/service manual that I can trust. Mostly looking for TP and Voltages at this time. After reviewing some of the other training manuals I feel I would learn a LOT more about Plasmas then I currently do.
3) I've read the horror stories about the IPM'S going out. I have a noticeable oscillating sound coming from one or both of mine. Is that normal or a sign that they are failing and possibly the cause of the blown fets?
4) I read on another post the recommendation of using FDB52N20 as a heavy duty replacement to the FQB46N15 that are currently installed. Any thoughts? At this point I am planning on ordering the heavy duty ones.
5) Are there any other parts I should consider replacing, in general and specifically related to the shorted fets, since I have to put an order in?
6) Was going to give this unit to my dad to replace his 30yo, non-HD, tube set. Am I asking for a lot of headaches and be better off selling it instead for something newer?
That's all my frozen brain can think of at the moment, have spent way to much time on this unit…..because I love every minute of the adventure of learning something new! Just love this stuff.
You guy's ROCK! Thank you for any and all thoughts/advice/input.
Randy
That makes sense. 
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