Samsung PS-50C91H 50'' Plasma tv

[joshnz]

Samsung PS50C91HX/RAD

Came to to me original fault watching it screen went blank sound working.

I got it here opened it up found 4 bad caps not changed them yet due to still in stage of working out what it needs/cost.

Powered it up sounded like it was running I moved it to look at screen and then the power supply went into protection, I turned it off then turned it on same deal traced issue to y sustain board took y sustain out found two shorted MOSFETS one looks to control the power to the bank of four MOSFETS where one was shorted.

My question is it safe to replace the two failed MOSFETS And see if that gets it running.

My concern is the y buffer, any idea to check for shorts.

[ReeceyBurger123]

Re: Samsung PS-50C91H 50'' Plasma tv

Here is a link to a video by Tom66 about checking Y buffer for S/C keep us updated if you find anything.

[ReeceyBurger123]

Re: Samsung PS-50C91H 50'' Plasma tv

These Ysus boards are junk what parts were shorted if its one of the five devices mounted on that little heatsink on the Ysus the buffer will surely be dead.

[joshnz]

Re: Samsung PS-50C91H 50'' Plasma tv

Ok link did not link

[joshnz]

Re: Samsung PS-50C91H 50'' Plasma tv

These Ysus boards are junk what parts were shorted if its one of the five devices mounted on that little heatsink on the Ysus the buffer will surely be dead.

OK buffer is in two parts upper and lower

[ReeceyBurger123]

Re: Samsung PS-50C91H 50'' Plasma tv

Sorry here you go: https://m.youtube.com/watch?v=51SZsfH60EY

[Alastair E]

Re: Samsung PS-50C91H 50'' Plasma tv

Almost guarantee there's a dead buffer-chip there--Usually the very Top one....

Buffers Kill the Y-SUS on these sets. You'll need to replace ALL the MOSFETS on that lower heatsink, And the one thats surface-mounted in front of that heatsink too, as well as all three 680uF caps on that Y-SUS board. Maybe you'll get lucky and there's no other issues Caused by the Buffer-chip failure.

DO NOT run that set with the original buffers fitted, without first CONFIRMING they are all OK or repairing. Doing so will kill the Y-SUS again, in an instant.

Regardless of previous info, these sets don't use 'junk parts' or boards. They are now getting Very very Old! Semiconductors, MOSFETS, Chips etc actually DO Wear Out now--partly due to the removal of Lead from their construction.....

--They would NOT have lasted for the 8-9 years before failing that they have, if they were junk!

[joshnz]

Re: Samsung PS-50C91H 50'' Plasma tv

Almost guarantee there's a dead buffer-chip there--Usually the very Top one....

Buffers Kill the Y-SUS on these sets. You'll need to replace ALL the MOSFETS on that lower heatsink, And the one thats surface-mounted in front of that heatsink too, as well as all three 680uF caps on that Y-SUS board. Maybe you'll get lucky and there's no other issues Caused by the Buffer-chip failure.

DO NOT run that set with the original buffers fitted, without first CONFIRMING they are all OK or repairing. Doing so will kill the Y-SUS again, in an instant.

Regardless of previous info, these sets don't use 'junk parts' or boards. They are now getting Very very Old!

--They would NOT have lasted for the 8-9 years before failing they have if they were junk!

I was impressed on how old this is seen lots of use to.
Will check buffer board now.

[Alastair E]

Re: Samsung PS-50C91H 50'' Plasma tv

Exactly! 5 years is Old for a TV set these days, 8+ is positively Ancient!

But--Better than the tosh they serve up in shops now, All gimmicks and plastic crap --which wont last till next Tuesday!
--Bit of an exaggeration --But not by much!

[joshnz]

Re: Samsung PS-50C91H 50'' Plasma tv

Gate drive mosfet on ymain is shorted.
upper buffer board has holes on second chip and 100mv on diode test.
model 50*HD W2A GVE YB(UP)
PCB LJ41-05121A

so so far it needs 5 odd caps probably more
6 MOSFETS $50
Y buffer board. $152

so will be about $200 to fix and that is without the caps

[Alastair E]

Re: Samsung PS-50C91H 50'' Plasma tv

Buffer chips are fairly cheap, but buffer-boards are pretty expensive,--and hard to come by--as its a known fairly common fault IF you get a S/H one--Test, Test and Test it again before fitting--Most vendors Do Not Test them.....

--I would replace both the dead buffer chip--and the very top one on that board with careful testing of the chips that remain, rather than trying to find a good board

[joshnz]

Re: Samsung PS-50C91H 50'' Plasma tv

Buffer chips are fairly cheap, but buffer-boards are pretty expensive.

--I would replace both the dead buffer chip--and the very top one on that board with careful testing of the chips that remain.

I don't believe I will be able to do the chip replacement I lack tools And can't justify buying them for one job well maybe more in future due to only one repair store here now.

I'll ask my customer but price getting up there.

I'll think about a hot air station Have needed one a few times but not often as i do repairs in my free time.

the buffer chips are only $10 each not too bad

[Alastair E]

Re: Samsung PS-50C91H 50'' Plasma tv

Got a hot air paint-stripper....?

Its what I use! Ally foil to protect surrounding board, and hot-air paint-stripper, Takes about 10 minutes to get 'em off, its not hard, just need patience.
--Issue is, The die in centre of the chip is also soldered to the board so you got to get the whole thing hot.

[joshnz]

Re: Samsung PS-50C91H 50'' Plasma tv

Got a hot air paint-stripper....?

Its what I use! Ally foil to protect surrounding board, and hot-air paint-stripper, Takes about 10 minutes to get 'em off, its not hard, just need patience.
--Issue is, The die in centre of the chip is also soldered to the board so you got to get the whole thing hot.

I seen the vias on the back of the board.
No but they cost almost nothing here I probably could borrow the tv owners one.

Anything in particular I should test on x board?

[Alastair E]

Re: Samsung PS-50C91H 50'' Plasma tv

X is usually OK, just check the 680uF caps on it and re-tighten the mosfet mounting screws--they always work loose, prolly heatsink washer shrinkage...

[joshnz]

Re: Samsung PS-50C91H 50'' Plasma tv

X is usually OK, just check the 680uF caps on it and re-tighten the mosfet mounting screws--they always work loose, prolly heatsink washer shrinkage...

check caps for swelling or esr?

[Alastair E]

Re: Samsung PS-50C91H 50'' Plasma tv

Just replace 'em.

[ReeceyBurger123]

Re: Samsung PS-50C91H 50'' Plasma tv

A bad buffer will not kill the Ysus on these its the Ysus that kills the buffer Tom66 has a video explaining what happens. Here is the link: https://m.youtube.com/watch?v=25HTy6esBHs
What happens is the Fets short and the sustaining period overloads which pops the buffer.
I recommend that you watch the video very informative.

[joshnz]

Re: Samsung PS-50C91H 50'' Plasma tv

A bad buffer will not kill the Ysus on these its the Ysus that kills the buffer Tom66 has a video explaining what happens. Here is the link: https://m.youtube.com/watch?v=25HTy6esBHs
What happens is the Fets short and the sustaining period overloads which pops the buffer.
I recommend that you watch the video very informative.

either way round i have a buffer ans a y main to repair as well as replace caps on psu.

I have watched video as soon as you fixed link.

[joshnz]

Re: Samsung PS-50C91H 50'' Plasma tv

hmmm should i...
http://www.ebay.com/itm/SAMSUNG-50-P...4AAOSwKOJYGZmc