Samsung SP-P4251 480P plasma VS fades out

[freakaftr8]

Hey all been really busy lately with family haven't had time to be on the forums.
well I have the Samsung plasma it old 2004 model. what happens is that after about anywhere between a half an hour to 3 hours of working flawlessly the vs starts to fade away dropping in voltage over a period of one minute to around 60v causing the image to get really dim. I have tried disconnecting the Z sustain and it will still do it. If I power down and power back up the pictures perfect again but the time duration for it to start dropping voltage again guess faster and faster until it will literally work for 5 minutes and I lose its picture again. When it's working there is no indication of any problems at all I'm assuming this is a problem with the power supply itself anyone had this issue and what should I look for?
All other voltages stay normal.

[freakaftr8]

Re: Samsung SP-P4251 480P plasma VS fades out

I can only assume without the schematic on the power supply that it may be the opto isolator or the control circuits for the VS rheostat.

[freakaftr8]

Re: Samsung SP-P4251 480P plasma VS fades out

When I say fades out it appears to pulsate and try to come back but gives up. The screen will actually go out altogether but try to come back at first. Then nothing. Audio only. Vs seems to hover low at this point. Around 60vdc

[tom66]

Re: Samsung SP-P4251 480P plasma VS fades out

Check if the PFC voltage is also dropping out at the same time.

[freakaftr8]

Re: Samsung SP-P4251 480P plasma VS fades out

Ok it appears it's only VS. VA and other voltages are consistent when this happens. No the PFC circuits are consistent as well when this happens. It may raise a volt or so.

[tom66]

Re: Samsung SP-P4251 480P plasma VS fades out

Picture of the power board?

[freakaftr8]

Re: Samsung SP-P4251 480P plasma VS fades out

Found it. 2 mylars .22k that crap out when cooled down. Heat them up and VS becomes stable again. They run off the VS mosfets.

[freakaftr8]

Re: Samsung SP-P4251 480P plasma VS fades out

well I went ahead and replaced the 2 Mylar capacitors that was not The problem it appears that 8 pin voltage regulator Ir2109 as I have lost VS and VA altogether now. oddly if I keep that area of the main relay starts clicking like crazy

[freakaftr8]

Re: Samsung SP-P4251 480P plasma VS fades out

I know this is an old post but I finally got around to working on that TV and I found the problem it was a 12 pin voltage regulator for the power filter correction circuit.