samsung ps-50q91hd

[attainteddragon]

main voltages
sticker/have
va 63 62.7
vs 207 205.6
vsc -195 unsure of test point
ve 90 14.97

no screen glow at all
disconnected x main and no change to ve
disconnected y main and no change to ve

[capkid]

Re: samsung ps-50q91hd

VSC is the same as VSCAN, and that test point is at the bottom of the Y-main.

[attainteddragon]

Re: samsung ps-50q91hd

thanks capkid.

vsc jumps to -193.7 and after a few seconds, it rapidly fades out.

[capkid]

Re: samsung ps-50q91hd

When the VSC voltage fades, do your VS and VA remain steady?

Edit: Do you notice anything onscreen when the VSC is normal?

[attainteddragon]

Re: samsung ps-50q91hd

everything else is stable.
though ve is way out.
no glow at all.

[Glitcher]

Re: samsung ps-50q91hd

Is there any sound when playing a source input?

[capkid]

Re: samsung ps-50q91hd

ok, yes, I forgot about the VE being out of spec. Do you have sound?

Edit: Glitcher, get out of my head

[Glitcher]

Re: samsung ps-50q91hd

It looks like this set uses the similar ysus and buffer boards as the HPT models that have those common no picture but sound faults. However I'm not sure if it'll have an effect with Ve dropping.

[capkid]

Re: samsung ps-50q91hd

I was thinking the same thing, and I shied away from the typical Y-Sus-Y-buffer issue because of the VE.

[attainteddragon]

Re: samsung ps-50q91hd

while your in there glitch, steal all his knowledge and send me a copy!

after stumbling around blindly, i can announce that i have sound!

[Glitcher]

Re: samsung ps-50q91hd

It might just be the ysus and buffers then.

Try this test with the buffer boards.
http://www.youtube.com/watch?v=51SZsfH60EY

Then test the Mosfets on the Ysus, mainly the ones facing closes to the buffers on the heat sinks. The common one to go bad is the one on the right heatsink in the far left I think it should be a 88N30W, you might want to try that one first. Other common failing FETS would be the K2837.

I recently did my first buffer repair, after replacing the IC buffer and FETs on the Ysus it came back to life! =D

[attainteddragon]

Re: samsung ps-50q91hd

looks like my top buffer chip has failed internally!

how did you go at replacing it. any tricks for removing the silicone?

i have to duck out to pick up another set now, so ill check the data sheets when i get back.

any other additional tips would be great! i think i have another 4 samsungs floating around at the moment and i might keep on these and try to learn a few new things!

thanks!

[Glitcher]

Re: samsung ps-50q91hd

Since you found a bad buffer chip that probably means AT LEAST one of the mosfets on the ysus are bad also. The fets on the ysus usually goes bad first which takes out one of the buffers.

To remove the IC I just scratched off as much silicone as I could with my finger and I wrapped it all in aluminum foil with a cut out and used a heat gun to heat up and remove the chip.

[capkid]

Re: samsung ps-50q91hd

https://www.badcaps.net/forum/showth...ghlight=Buffer

https://www.badcaps.net/forum/showth...ghlight=Buffer

[attainteddragon]

Re: samsung ps-50q91hd

all of the 88n30w mosfets are cactus!

i havn't found anything else yet. is there anything in particular that i should focus on.

i think that ill have a go at the buffer chip. it will be a good learning experience and i know that i have at least one more with the same problem.

i thought that i would cut a lead template for when i try to remove it. should protect the neighboring components fairly well i think!

[tw2005]

Re: samsung ps-50q91hd

all of the 88n30w mosfets are cactus!

i havn't found anything else yet. is there anything in particular that i should focus on.

i think that ill have a go at the buffer chip. it will be a good learning experience and i know that i have at least one more with the same problem.

i thought that i would cut a lead template for when i try to remove it. should protect the neighboring components fairly well i think!

Were the FETs in cct or off the board? They may not all be bad but I know if 1 is short the rest will show short in cct. They're cheap enough from china. Done 3 of these ymains i think the least shorted I had was 2 FETs.

[attainteddragon]

Re: samsung ps-50q91hd

i havn't pulled them out yet, but i was a bit worried about how sensitive these samsungs are, so i was prepared to change them all out if needed!

ill order a few extras since i have a few of these to do!

not sure if i want to become a master at these type of repairs though!

[tw2005]

Re: samsung ps-50q91hd

i havn't pulled them out yet, but i was a bit worried about how sensitive these samsungs are, so i was prepared to change them all out if needed!

ill order a few extras since i have a few of these to do!

not sure if i want to become a master at these type of repairs though!

easiest repair as far as Ymains goes but as for the buffers, very hard and expensive to get the boards but anyone with hot air and skills to do so replacing the chips is a viable option, not me though.

[capkid]

Re: samsung ps-50q91hd

Did you go to the links I provided? Some of the gotchas are mentioned there.

[attainteddragon]

Re: samsung ps-50q91hd

i have my parts for the y main coming. that part of it will be easy, but the buffer chips will force my practical skills up rather quickly i think.
i have at least two of these sets with identical failures and im sure if i pull this off, i will find many more to do.
i have a scrap board to practice on, and you never know, i may end up with a spare if im lucky.
you know how hard it is to get most boards in aus (at an acceptable price), so im getting use to these intricate repairs.

cap, i looked through those links and im still a little worried about removing all of the silicone at the moment, but im sure ill sort it out somehow. i was thinking about using silicone removing gel to break down the trace particles, but im worried it may have an adverse affect on the board. fun, fun, fun!