Samsung PS-42S4H flashing pixelated screen

[wrx884]

Have been given this Samsung plasma PS-42S5H for free to have a little play with and see what I can do with it and mayb have it up and running as gaming test TV.



Problem is the screen flashes on and off continuously with a pixelated picture to a blank black screen like this when powered on:




So far from some doing research I have found the top and bottom Y buffer boards are the boards that need replacing so I did some investigating and found 1 of the IC's was blistered and sure enough when u power on the TV it glowed red and pulsed on and off with the flashing of the screen.

bottom Y buffer board:



Now ive found replacement IC's and have soldered on the new IC, now there are no shorts on any of the IC's on the buffer boards so Im sure these are good to go now. what do I check next? i am now un sure what else to check as I fear something else in the chain link has caused this issue so id rather not blow the new IC if I can (I do have another 3 spares just in case lol).

Ive never repaired a TV before so board names and some components are new to me (I have found a schematics pdf tho if it helps?) but I do have a general idea of looking for burnt components, blown fuses, bulging caps ect.... and so far I have found none. what tests can I do now before installing the buffer boards again so they don't blow? I have a DMM on hand so hopefully it will come in handy, also have a capacitance meter and ESR meter on the way too and all soldering gear needed.

cheers for any help.

[newtothis]

Re: Samsung PS-42S4H flashing pixelated screen

Quick question first as from your post it seems you are quite new to electronics in general.... How much soldering experience do you have?... If very little I am shocked you managed to remove and replace a package with such fine pitch! If you managed to get all leads to solder to the pads and no bridges etc I applaud you!

May I ask how you checked the boards for shorts?

You will want to check your Y-Sus for any bad fets.

[wrx884]

Re: Samsung PS-42S4H flashing pixelated screen

Quick question first as from your post it seems you are quite new to electronics in general.... How much soldering experience do you have?... If very little I am shocked you managed to remove and replace a package with such fine pitch! If you managed to get all leads to solder to the pads and no bridges etc I applaud you!

May I ask how you checked the boards for shorts?

You will want to check your Y-Sus for any bad fets.

cheers I do a lot of car electronics and audio installs which lead to repairing ps3's strangely enough and now just learnt how to downgrade them which consists of removing the NAND or NOR IC's at times so I treated this IC the same pretty much, so I guess my experience in the reworking side of things is quiet good. I have my own BGA rework station, hot air wand, solder and de-solder stations so I have all the gear pretty much to do this work which is why ive jumped another ship to learn about mayb repairing TV's on the side too, or mayb just this 1 haha. but I will say my knowledge for some board components im still learning a great deal (proper names and how to test them ect.....) which is why I need some guidance on what steps to take next.

since im also working from the schematics too can u tell me which is the Y-sus and how to tests bad fets? fets are mosfets yeah? im guessing its the Y drive board that ur talking about too? I did noticed names of different boards in TVs were used on this forum and are not the same as whats in the manual to some degree so just so we are on the same page can u just confirm I have the names correct?



testing the buffer board IC's basically I just tested for shorts to ground and shorts to the power using the DMM set on diode mode. put probe on the ground pins on the buffer board and then ran my other probe along all 6 ribbon connectors legs to see if there were any shorts and sure enough the only connector to show a short was the IC that had blistering on it. This saved me time doing it this way because they had their heat sinks on at 1st and I couldn't actually see the damaged IC but the test lead me straight to that IC at least and once the compound was taken off the top of the IC I could clearly see the blistering on the IC. now that I have replaced with the new IC I have no shorts and have inspected all legs have been soldered properly.

[newtothis]

Re: Samsung PS-42S4H flashing pixelated screen

Just got myself a rework station, It is actually down at the office after being delivered today, Got a BIRD AC 5000 (2000w bottom IR and 500w top IR) now just waiting for all my other accessories to be delivered (Reball Jigs, IPA, MEK etc etc) then I can get to burning lots of boards while I practice LOL

Nice to see someone do a little research before getting here!

Y-SUS is #3 (Y Drive Board)

From thread - https://www.badcaps.net/forum/showpo...4&postcount=19

"If you have a manual range multimeter, set it to 200 ohms (two hundred). This is for 3 pin ICs only. You can test a mosfet (Q, IC designation) "in circuit" by (power off and unplugged)

a) black on pin 1- red on pin 2 - record ohms
b) black on pin 1- red on pin 3 - record ohms
c) black on pin 2- red on pin 3 - record ohms

If any reading is less than 30 ohms you might have shorted mosfet. Remove from circuit and repeat the tests to verify.

Some mosfets are more than 3 pins. To test those, identify the part number and search for its datasheet. Once you find the datasheet, the pins will be designated source (S), gate (G), and drain (D). It will probably be documented as S1, S2, G1, G2, D1, D2.

Simply test

a) black on pin S1- red on pin G1 - record ohms
b) black on pin S1- red on pin D1 - record ohms
c) black on pin G1- red on pin D1 - record ohms

Repeat for the "2" pins. That is S2-G2, S2-D2, G2-D2."

There will be a bank of them on the heatsinks that need to be checked

[wrx884]

Re: Samsung PS-42S4H flashing pixelated screen

hope im not reading this wrong but I have removed the heat sinks from the mosfets labeled (Q****) but I can not get any reading with my multimeter set on 200ohms? I can however if its set on 2000ohms is that sufficient readings?

[Th3_uN1Qu3]

Re: Samsung PS-42S4H flashing pixelated screen

It is good that you get no reading, that means they aren't shorted. Try repeating the test using the diode function of your multimeter, you should get some readings there.

[wrx884]

Re: Samsung PS-42S4H flashing pixelated screen



(component marked in yellow I removed for testing purposes)

ok ive tested all mosfets in red using diode mode now and got these results:

(Set on diode setting)
• Q5002- a)1 b)985 c)614
• Q5004- a)1 b)976 c)611
• Q5006- a)1 b)1205 c)532
• Q5005- a)1 b)1213 c)542
• Q5007- a)1 b)1228 c)543
• Q5008- a)1 b)1227 c)541
• Q5009- a)1 b)1231 c)543
• Q5010- a)1 b)1230 c)530
• Q5011- a)1 b)1212 c)533
• Q5003- a)1 b)1030 c)585
• Q5013- a)1 b)1044 c)585

ive check other mosfets? there's 2 marked with D5027, D5028 in blue in pic above, are these the same as the Q**** type above? ive measured using my DMM set on 200ohms anyway and get these result.

a)1, 1
b)00.8, 00.8
c)1, 1

now using diode mode:

a)1, 1
b)002 with constant beep, same constant beep and reading.
c)442, 471

Theres another marked U5001 (is this the same also?) in blue far right in the pic above:

a)1
b)1
c)1

diode mode:

a)1
b)1
c)1

awaiting next set of instructions or advice cheers.

[Th3_uN1Qu3]

Re: Samsung PS-42S4H flashing pixelated screen

Your mosfet readings look good.

D5027, D5028 should be dual power diodes and the readings you are getting are normal. U5001 is some kind of integrated circuit. Not shorted is usually OK.

I don't see anything obviously wrong with your readings. You should wait for a 2nd opinion, but it looks all clear to me.

[newtothis]

Re: Samsung PS-42S4H flashing pixelated screen

Look good to me.

Not sure if there is anything else you should check before testing, Wait for Tom to chime in

[wrx884]

Re: Samsung PS-42S4H flashing pixelated screen

ok thanks for all ur help so far guys much appreciated, who is Tom tho? I may pm him if he doesn't end up spotting this thread.

[wrx884]

Re: Samsung PS-42S4H flashing pixelated screen

any other help that can be advised? cheers

[newtothis]

Re: Samsung PS-42S4H flashing pixelated screen

Tom is one of our Elite in electronics... Very informative and knowledgeable, Budm is another.

As far as I can tell you are good to test it, but I will ask one of the other guys to read over this when I spot them online

[newtothis]

Re: Samsung PS-42S4H flashing pixelated screen

Quote from Tom

"You should also check Vsch (not the same as Vsc) on Y-main, if this is low, high or negative it can kill the new buffers."

[wrx884]

Re: Samsung PS-42S4H flashing pixelated screen

Quote from Tom

"You should also check Vsch (not the same as Vsc) on Y-main, if this is low, high or negative it can kill the new buffers."

OK great tho do you care to elaborate more on how to do this and where I would find the vsch point ? I haven't got the board in front of me to check I'm guessing the boardwill be marked vsch?

[tom66]

Re: Samsung PS-42S4H flashing pixelated screen

Vsch is not always marked on Samsung sets. It is about 120-160V relative to the Vsc point.

Usually Vsch can be measured between the Y-buffer floating ground and VH. The floating ground usually has a lot of connection pins dedicated to it. The VH usually has a few, more than most, but less than floating ground.

[wrx884]

Re: Samsung PS-42S4H flashing pixelated screen

Vsch is not always marked on Samsung sets. It is about 120-160V relative to the Vsc point.

Usually Vsch can be measured between the Y-buffer floating ground and VH. The floating ground usually has a lot of connection pins dedicated to it. The VH usually has a few, more than most, but less than floating ground.

I think I know what u are talking about now if im correct I noticed this when testing the top and bottom buffer boards for shorts?

So in that case im guessing VSCH are the lighter green PCB trace (floating ground) and the VH is where the darker green traces are?

connector CN5002:

So lets say pins No. on top connector on y drive board VSCH is seen connecting all pins by the lighter green pcb trace? and VH is pin 1,2,3,4?







Connector CN5001

pins No. on bottom connector on y drive board VSCH is seen connecting all pins by the lighter green pcb trace? and VH is pins 35,36,37,38? pin 1 and 2 here looks like it links up to the other connector CN5002 is this also a VH point?





To check this voltage I would have to install the Y drive board back in and hook everything up except for the top and bottom buffer boards and power the TV on and measure its voltage that's mentioned is that correct?

[wrx884]

Re: Samsung PS-42S4H flashing pixelated screen

any more input here guys? cheers.

[wrx884]

Re: Samsung PS-42S4H flashing pixelated screen

can anyone else offer any help?

[tom66]

Re: Samsung PS-42S4H flashing pixelated screen

I can't see any pictures -- can you upload them here directly?

[newtothis]

Re: Samsung PS-42S4H flashing pixelated screen

Pics from previous post