Friday, March 26, 2010

How to identify burned buffer boards LJ92-01203A LJ41-02761A LJ92-01202A LJ41-02760A

(UPDATE 25 Oct 2010  - I have added another article with additional details on the subject. Find it here.)
(UPDATE Dec 2012 - now the Y-Main and a set of brand new, Samsung OEM buffers is available at our store.)
(UPDATE Feb 2013 - our store now has listings for both the upper buffer LJ92-01202A and lower buffer LJ92-01203A - used, but tested and functional, offerred as-is; make sure you read this article and offer description before buying!)

Here's a very simple and easy method of identifying burned buffer boards LJ92-01203A / LJ41-02761A  and LJ92-01202A / LJ41-02760A.
Those are the buffers for Y-sustain LJ92-01200A.

The trio is used in a great number of 42'' plasma TVs using Samsung plasma display technology (the display itself and the sustain/buffer boards).

It is also famous for its common failure. The most common scenario involves burning the Y sustain which subsequently burns one or both buffers.

Now, to the point: The most common defect in those buffers manifests itself in burning and shorting the power lines and some output lines.

The easiest way to detect if a board was burned is to measure the resistance between its power input and ground.

Normally it should be in the range of hundreds of kOhms and when burned it is usually a matter of Ohms.

In fact, you can use the diode/audio test mode to determine if a board is burned or not.

Still , in the below examples, I am using a multimeter in a standard resistance meter mode.


On the TOP buffer board, the power lines are the top two lines of the black connector and ground are the most of the remaining connectors.

On a good board the resistance between the two may be too big in the proper direction and about 500kOhm in reverse direction.

The board on this picture is good.






On the bottom board the power lines are the bottom two lines on the black board and ground is above them.

In the example picture on the right the resistance there is only 4.4 Ohm clearly identifying this board as a burnout.

The resistance would typically be the same in both directions.

This board would prevent the TV from powering on and may also burn the Y-sustain board.

In a future post I'll also show how to identify the particular ICs on the burned board.



19 comments:

Kevin said...

Thanks for your articles, keep em coming!

rdc02271 said...

Hello.
One quick question?
Does anyone know who manufactures the lj92-01200a board?
Yes, I know Samsung sells them, but they don't provide schematics for the board!! Not even to companies like ours that are official workshops (i.e. we have a contract with Samsung to give technical assistance to their customers).
Hence my question.
What company actually develops these boards?
The same thing happens, for instance, with Grundig.
It's a ridiculus situation. Most times we are able to fix the board, but the problem is complex having a schematic would really help.
Especially when the alternative is to buy a new board - the customers often say:
How much?! 150 dollars. Are you crazy?! Thanks, but no thanks.

So to wrap up, has anyone found shematics for these boards?
Thanks.
Jorge C.

David said...

I am fairly sure that both of my y buffers are burnt (based only on the appearance of horizontal bands of discoloration on the panel - I haven't yet verified with the method described above). How do I know if they were burned by the y sustain? You seemed to suggest that the root cause of the common problem with the buffers is the Y sustain. I'm sure the best course of action would be to replace all three, but I am on a pretty tight budget so I'm hoping to avoid this.

Thanks
David N.

Coppell TV Repair said...

It's usually the buffers that burn the sustain, not the other way around.

Granted, it may happen for the sustain to go first, but in the vast majority of cases that I see the buffers go bad and kill the sustain.

In this particular trio there's no much room for consideration...a buffer is either good or no good and the only COMPLETE way to tell is to test it.

Unfortunately, if the buffer is bad, it may kill the sustain...which is the sole reason why it should be tested by experienced technician. First, we know when to pull the power cable and second and most important, we know how to service the Y sustain if we need to - alas, happen more often than it should.

Meestermole said...

I have a Samsung HP-R4262, the symptoms are a snowy looking picture (even on menu) with horizontal lines.

Ive checked and set the following values thus far:

Va Vsc Vs Ve Vsel
70 -185 206 84 195

I'm trying to isolate what is my faulty board, however following this post, I come up with the following resistances for my buffer boards:

Upper board = 17.55 MOhms
Lower board = 14.43 MOhms

are they good? could it be the sustain (Y-main?)

Derek said...

So I take it that the IC's go bad in the buffer boards? looks like you would have to be awefull good at soldering to replace one of those baby's. Do you ever find any of the other surface mount components bad? My situation is that; once the lower buffer is removed, the TV will turn on and i get the top half of the picture. I also have replaced a bad cap: c5040 on the sustain board and the two c5059 and 5060 caps on the power supply. Do you guys repair the buffer boards? Also, please post common problems to check for on the sustain board. thanks! keep up the good work!

Derek S said...

Ok, Ive had a bit of soldering practice and and ready to find and replace the bad IC's. I have verified that the lower buffer board is shorted 5.5 ohms. Looking at the bottom of the board, it looks like it may be possible to probe the different pins on the IC's, but my questions is, which pad leads to which leg? and which leg on these IC's is the power supply?

Travis said...

What is the diode/audio test method? I am trying to test my boards to see if I need to send you all or just one in order to have them repaired and sadly my multimeter skills are lacking. I wasnt able to get understandable results off the pin resistance tests.

Bobby Kolev said...

@Derek S - I think in another post, before leaving for vacation in Summer 2010 I described how to find which IC is shorted.
You don't care about which particular pin of it shorts - any short on the output connector indicates bad IC and all pins there go to one of the two ICs that are next to the connector. It's easy to figure which of the two since at least one of the connector's lines can be visually traced to an IC; the lines on the opposite side of the connector go to the next IC.

Which pad is power supply - well there are many. I may publish the pinout of the IC one of these days.

@Travis - turn the multimeter in "diode test" mode indicated by a diode. if you touch the two probes the multimeter produces a beep thus indicating a short. Well next connect one of the two to the ground input (multiple connected lines in the middle of the black connector) and start probing as shown on the picture.

Brandy said...

I have a norcent 4291hd that has the same parts as these. Unit powers on and seems to power off and clicks 3 times there after, maybe relays? One of the transformers on the lj92-01200a board is hissing. Two heatsinks on the other lj92-01202a board are extremely hot. I am assuming that its toast. I bought the entire Tv for $10 hoping to fix it. When we turn it on in the back there is an red LED flashing. Anyone know what may have caused these problems? We already took the boards off and re-soldered anything that may need soldered, cleaned the board, and did not see any evidence of caps being bad. Is there anyway to fix it without spending a fortune? The boards to replace them are pretty high and i don't see spending $300 on boards when I can buy a new TV for that basically.

Bobby Kolev said...

First read the entire posting, then pay attention at the link at the end. You'll find the answer to your questions.

serwis said...

Hello,
thank you for your great posts. Your "resistance method" helped me a lot. I have measured resistance in the top buffer board and my results are: infinity in the proper direction and 4,2 MOhm (MegaOhm) in the reverse direction. If I understand you properly that means the board is faulty?

Chris said...

I am reading 4.7 MOhm in the opposite direction on both my upper and lower boards. Would this indicate that my boards are bad or not? I also have red lines going horizontally across my whole screen... thanks, i am hoping to get this fixed asap... i also have a single bulging cap on the Y-Sus board (C5041) Thanks in advance for any help you all can give me!...

Pat said...

How to test a LJ41-03432A buffer board? I have find 3 RJH3077 on my y sustain board are bad. I have order these part( after a month of research) And I dont want to burn it again...
Thank you!
Pat

yamahadude said...

so if i put my meter on the setting with the audio tone and i get a tone when probing the power and ground as described then the board is bad correct ? thanks

gpatel said...

I've got the same boards on a tv I'm trying to fix. I've done the test to check the IC's and I'm getting 11 out of 12 IC's bad. I was wondering how and why would so many blow? The posts I've seen people only get 1 blown and I've got nearly all of them. Any info would be great as it's my first tv fix and I'd like to know why things blow on the board rather than just fix it. The large IC on the Y board is bad too. I used the check in your blog, thank you! :)

B Atkins said...

I was wondering if you'd noticed a trend regarding which ICs on the LJ92-01202A and LJ92-01203A buffers typically fail. The few boards I've seen usually have one or both of the ICs farthest from the connectors fail.

2941a8ee-dc51-11e2-b53b-000bcdcb8a73 said...

great site, thanks for all the useful info.

I have a samsung hp-t5064 that has sound but no picture. also has a burning smell. I pulled the back off the set and found what looks like a burnt chip. the board that it's on is this part...

Samsung BN9606520A (LJ92-01491A) Upper Y Buffer Board

its the second chip from the top.

can i just replace the board or is there some other thing that is causing that chip to burn? thanks,

MarqueeLongbow said...

I have a LJ41-02319A set of buffer boards from a 50 " philips Plasma. I repaired both the Y and X SUS board and some voltages that were not present on the PS. All was good on first power up. I shut off the TV and checked how it power on via the power button since the TV turns on as soon as it is plugged in. So it was on for about 20 seconds then the YSUS fuse blew, both IPM's were fried. Short GND to SU. Before i fired it up I did a test of the Buffer boards but did itby holding the one probe on the GND and ran the other probe along the output pins from each board on both sides of the connector. no shorts. But is that a good way to test this version Buffer? what are the pins I should check on this board?

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