samsung 50" plasma Yscan voltage low?

[datajoecool]

well after doing all the possible checks on Samsung hp-t5064 plasma. i am only getting -20 volts out of vscan. have good voltage everywhere else. This negative voltage stuff really confuses me. I imagine it is a FET but i am not sure. I will probably order a board but i like fixing things not just replacing things. thanks in advance. joe

[datajoecool]

Re: samsung 50" plasma Yscan voltage low?

wow that is weird! when i turn tv off the negative voltage jumps up to the correct voltage and then slowly drains down as i watch on the meter. I also want to check if there is only suppose to be 14 volts going through the little green fuse.

[datajoecool]

Re: samsung 50" plasma Yscan voltage low?

ok, bad lower y buffer took out Ysus board. Now which parts on sus board are bad. I see kits on ebay. Hmmm.

[ReeceyBurger123]

Re: samsung 50" plasma Yscan voltage low?

No no, these Ymains are prone to failing in that way. What happens is the Ymain normally kills the buffer. Did you check it for shorts ?

[datajoecool]

Re: samsung 50" plasma Yscan voltage low?

well well well. I just put a pair of of buffers and y board in i got on ebay. And I checked the buffers first. And! well. I turned on the tv and the screen sparkled and then the y board began to smoke. And to my pleasure everything is bad now.
Reecey I love your "never give up!" mato. I do not want to give up. So. I have ordered a bunch of components for my learning. And yes i checked for shorts on the buffers and they were good but not now. I have ordered ic's to practice my surface mount skills and try to bring these back to life. My problem now is i for the life of me find the problem parts on the y board. i pulled the mosfets off the board and they all check good with my esr meter. and the tester circuit i made from the internet. But, when i try to do that ohm meter test it does not work. You know triggering the gate with the leads. None of them do. Mosfets check, caps check. what went up in smoke?
One question i have is it possible for the display to be shorted?
Thanks. banggin my head on table.

[Alastair E]

Re: samsung 50" plasma Yscan voltage low?

If its the Y-SUS I think it is--Difficult to say without a pic--

Then the smoking will prolly be from a TO220 SMD MOSFET mounted near the bottom heatsink...

The other IGBTS/MOSFETS also mounted on that bottom heatsink--All 5 of 'em will prolly be short too....
--Common fault. Sometimes Buffers kill these Y-SUS, sometimes other way round....

[ReeceyBurger123]

Re: samsung 50" plasma Yscan voltage low?

Right, watch this video will help you alot:

https://m.youtube.com/watch?v=25HTy6esBHs

[ReeceyBurger123]

Re: samsung 50" plasma Yscan voltage low?

When soldering the Ic on be VERY careful you can damage the traces very easy. What you will need to do is:

Scrape glue off around Ic.
Heat Ic with hot air until solder is molten.
Lift Ic with a sucker or tweezers.
Clean all pads with solder braid, add flux as it helps original solder get sucked up easier.
Clean with ipa.
Scrape excess glue off.
Add fresh solder to middle pad only a small amount needed.
Apply flux to centre pad.
Begin heating with hot air until centre pad is becoming molten.
Drop new ic on top.
Continue heating until Ic flows in to place.
If done correctly the ic will be flowed into place properly and all pins aligned ready to be soldered.
Check alignment of all pins make sure they are in place properly.
Flux all pins.
Tim you iron end, drag out across pins solder should take to them.
If not use fulx and solder braid to wick up old solder.
After all pins soldered clean with ipa.
Check solder joints.
Apply layer of hotglue to stop dust causing any interference.

This is hard to do but when you do one you can normally do others with ease, use good flux, a hot soldering iron (above 360c) also take your time.

[ReeceyBurger123]

Re: samsung 50" plasma Yscan voltage low?

Also best to use a DMM in diode mode to test them fets.

[datajoecool]

Re: samsung 50" plasma Yscan voltage low?

Ok. I had my question answered from the guy i bought the boards. He replied. He said these boards were taken from a functioning tv and if they blew that indeed the display is shorted. Fantastic.
I watched the video. good one.
Now my problem is fix all these things and do what? I have found no way to test the display for shorts.
reecey. those ic's will be fun. I have watched several videos on installing new ones. And those mosfet tests. Like i said with the dmm they do not check good. none of them. but with the other testers they check good. the esr meter shows all numbers close to the same and the little breadboard circuit for testing tell me they are good also.
Alastair, i am going to check that fet now. And i can not see a speck of damage anywhere. not a burn, not a bulge.
Oh boy, i now have two blown boards and four bad buffers to play with. yayyyyy
thanks guys

[ReeceyBurger123]

Re: samsung 50" plasma Yscan voltage low?

These Tv's are a nightmare, the plasma panel being shorted is VERY unlikely, his boards were probably fine your Ysus would have killed them.

[Alastair E]

Re: samsung 50" plasma Yscan voltage low?

TBH--Not had a genuine shorted plasma panel yet....

Had many that have had cracks or COF chips bad, but none shorted.

These sets are a bit of a ball-ache I usually install the Y without buffers, run it to check all is well for a while, no overheats, normal 'buzz' and test the buffers extremely well before refitting 'em....

[ReeceyBurger123]

Re: samsung 50" plasma Yscan voltage low?

Believe it or not even if the Ymain is shorted it buzzes like normal lol the one heatsink just doesn't get hot. Stupidly the protection circuit doesn't kick in until the buffer is incinerated.

[datajoecool]

Re: samsung 50" plasma Yscan voltage low?

Ok. I am sitting here watching doctor who waiting for parts. Keep you posted when they arrive. Now i have time do do some more studying. Wish i had a sonic screwdriver.
thanks

[datajoecool]

Re: samsung 50" plasma Yscan voltage low?

Ok again. well who would have thought 3 different components from three different venders in china would all arrive here the same day. and the nice Chinese vender gave me a extra ic buffer chip.
And i just found something interesting. I just happened to glance a google note that said your dmm must put out a sufficient voltage for mosfet tests to work. And of course my new dmm does not. so i pulled out my dmm from school in 1978. and now my mosfet tests register. learn something new everyday. Now we need time to gather our brains. Electronics has always been gods little tease to me.
Until the next post.

[freakaftr8]

Re: samsung 50" plasma Yscan voltage low?

It is common for this Y board to blow v MOSFETs on the output rails to the buffer boards. The two nd MOSFETs are Toshiba MOSFET and the ones in the centre are a different vendor. These are known to fail along with a couple MOSFETs that are soldered directly to the y board. These are st series. This is a tricky board. Even if the MOSFETs don't test shorted they can still be bad thus destroying buffer boards

[ReeceyBurger123]

Re: samsung 50" plasma Yscan voltage low?

The Toshiba fets dont ever normally fail, the 88N30W think SK always seem to quit on these, I think its because over time they fatigue and cant withstand the sustain set up pulse and dont switch fast enough and go S/C which then sends that to the buffer killing it. They fatigue like at because of how hot they run, mounting 5 power fets on that crappy heatsink and with how hot these get anyway just causes them to wear out. They always fail on start up as well so it is something todo with them not switching fast enough during the set up period and taking too much current. Crappy Ymains in general.

[datajoecool]

Re: samsung 50" plasma Yscan voltage low?

ok. I am waiting on two other mosfets. I did notice on the toshiba when i tested with the dmm it would jump negitive once the gate was excited. I do not think it is suppose to do that! And the new ones do not. I have my 3027's and 2837's waiting for 88n30w's and surface mount fets. and I have the buffer ic's. Now just need to organize a work space to do these. Are the panasonics and texas inst,s interchangable if it is like only one?
Because one set of buffers are pan,s and the others texas. I am going to try to video this if possible.
May i ask also, My friend who gave me this set told me today. He would see some sparkle on the screen when no image was being displayed. in other words blackness. Is sparkling of the screen a sign of bad display or a sign of slow component failure?
and from you guys knowledge i guess replace everything. Fresh is better than stressed!!!