Monday, October 25, 2010

LJ92-01200A / LJ41-02759A - the truth according to me (feat. LJ92-01203A / LJ41-02761A and LJ92-01202A / LJ41-02760A with 6 ICs)

(December 2012 update: a set of replacement Y-Main and two brand new, OEM buffers is now available at our store for an exchange service. Still, please read the article before proceeding there!

(February 2013 update: 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!)
I've been planning to post this for a long time, but various things have been stopping me until today.

This article summarizes some of my experience with the infamous Samsung 42'' plasma trio of boards:
1) The Y Main sustain LJ92-01200A / LJ41-02759A
2) The upper and lower buffer boards  LJ92-01203A / LJ41-02761A and LJ92-01202A / LJ41-02760A

(Note: this article is about the A1, A2, A3, A4 and A5 revisions manufactured in 2006/2007. In 2010 Samsung has released new versions of those boards with four instead of six buffer ICs. It is far too early to know if they have the same flaws as the old ones. They have, for example, apparently different design and implementation and newer ICs may be better than the older SN755867 and SN755870.)

We at Coppell TV Repair often receive questions about those.

Do we repair buffer boards?
How much would it cost to have all 3 replaced?
Do we mind sharing what goes bad on the Y-Main? (this is usually from other technicians)
Are the new buffers better?
Should the customer invest in repair or junk the whole TV?

Some of those questions do not have simple straightforward answers.

I really wish it was that easy. But it isn't, not unless you want to take the king's approach to it and replace everything. Which, as reality shows, tends to be rather expensive exercise.

I truly believe that one of the humanity's major flaws is that it often tries to fix something without understanding what actually had been broken in the first place. Stepping more on the gas instead of releasing the hand brake , treating kids for ADD instead of spending more time with them or taking pills for depression instead of stopping to listen and watch to the media reporting rapes, kills, recession and end of the world in general....just a few from the top of my head.

Sorry, got carried away.

I want to tell you what happens and how it happens.

Don't forget, it is all according to me and although I have a graduate in electronics I am much better in software than hardware.
Some of my guesses may be wrong...if you catch one I'd appreciate bringing it to my attention.

Let's start with


There are two possible problems here: when a buffer fails without shorting and when a buffer fails completely.

When a buffer fails without shorting it typically results in horizontal pink/purple lines. They can appear at isolated portions of the screen or on the whole screen.

Such horizontal lines of pink / red sparkles is clearly a buffer on its way out. To see it full screen just click on an image. (screen shots submitted by customer Jason Stubbs , a man with a good taste :-)):

This problem can NOT be  detected with a meter or at least I do not know how, but as I said above if you see those lines you your buffers need to be replaced.

What if only the upper/lower half of the screen has those? Well, read on as to why it happens and you'll understand.

The SECOND, ultimate and actually more popular buffer failure is shortage.

While the pink lines described above is only a partial failure which damages the control logic in the buffer ICs, but still doesn't completely kill them this one does.

A full failure is caused by a more massive meltdown in the IC during shortage and usually results in a an electrical shortage between the power lines of the buffer.

(If you want to check if your buffer is shorted use the technique described in an earlier post.)

A burned buffer usually takes the sustain down and since both buffers are on the same power track without separation one failed buffer usually damages the other one as well.

But why does it all happen in the first place?

Because electronics wears out.


I have two theories on what exactly is wearing out more: one is the semiconductor  junctions inside the buffer board ICs are wearing out because of the temperature differences between state at rest and state at work: when they work they get hot, the matter expands and changes structure, even by a tiny little bit, then when it cools off it shrinks and the little change remains. Over time, a micro-space develops as a defect in the semiconductor junction which one day leads to a shortage.

The other theory is that the insulation material they use for covering the IC pins changes properties over time, allowing for a high-voltage spark to jump from one pin to another, i.e. from a high-voltage output to a low-voltage power supply or control pin.

Over time I started leaning more towards the first theory as the same thing tends to happen in other components that do not have silicon insulation over their pins.

Each theory might be wrong, of course, but both are too good to explain what happens to ignore :-)

So the IC burns, melts and shorts.

That causes a momentarily overload to the Y sustain board which also burns one or more output components.

Finally, since the two buffers share common data and power line without separation any high-voltage jumping to the shared low-voltage power or data tracks tends to damage whatever it finds there that is not designed to handle it. Imagine placing 120V on a 5V data line....what do you expect?!

Which means that whenever a buffer shorts, usually all three boards end up being damaged!

The second buffer is not always shorted. Sometimes - in fact most of the times - it looks like normal, but will burn upon its first run in real condition.

Conclusion 1? When a failure is caused by a burned buffer LJ92-01202A or LJ92-01203A it is best to replace BOTH buffers.

Doesn't sound convincing? Well lets then empower the real heavy artillery, something very simple we almost said it plain, but you missed it:

Buffers wear out! Literally.

If our explanation is right and the silicone insulation on the buffers wears out due to the high temperature....until one of the buffers doesn't hold any much longer do you think the other buffer will be able to carry on?

Think of it this way: if say the front two tires on your car wear out to a point where one of them tears out while driving...will you replace only that tire? And why?

Knowing that the failure of one buffer carries high risks of taking down the other...and knowing the buffer prices (which are anything but low) it's a no-brainer!

REINFORCED CONCLUSION 1: When a failure is caused by a burned LJ92-01202A or LJ92-01203A buffer it is BEST to replace BOTH buffers.
 Note: Sometimes the buffer defects in a way that does not immediately result in a complete short, but rather in a visual defect represented by pink / red sparkles in horizontal lines on the screen that vary from 1/6 of the display to the full display. When it is on the full display this can also be confused with another popular problem which has nothing to do with the buffers, but rather the Y sustain board.

Note 2: Buffer boards can be repaired sometimes, however most of the time it doesn't make practical sense for the very same reason for which it is best to replace both buffers when one dies: all ICs on the buffer board have been wearing out together and replacing one or two of them at a time, while fixing the problem temporarily, does nothing to prevent the soon-expected failure from another IC.
And replacing all 6 usually costs more than buying a new buffer.

While there is still what to be said about those buffers, we'll wrap it up for now and will switch our attention to


The same truth that holds for the buffers also holds for the sustain board  LJ92-01200A  (and in fact for all electronics) - heat wears them out.

But before we get to that we'll start with the one problem that's not caused by the Y sustain itself:

When Y Main sustain LJ92-01200A is damaged by a burned buffer
As we said earlier when a buffer shorts it usually takes down the sustain along with it.
Once damaged, the sustain may be damaged in a way such that, if you install new buffers, it will kill them on the first run.
When we say may we mean it happens. Not too often but still often enough.


Note: This is the only Y sustain failure that I know of as of the time of this writing that presents a danger to the buffer boards!

I hope I will be forgiven for not telling you how exactly to repair this failure. I'll only say there are several common scenarios and information for some if not all of them is likely available around the Net.
As I've mentioned before we know there are other technicians who monitor this blog and start competing with our services on Internet based on what they get the point.

(Frankly, no offense meant, but from my contacts in the past months with various such technicians around the country I think they don't even know most of what's in this article...but that's another story; and still those are better than the ones reading what others say and then stating it on their listings and not giving credit to their sources!)

Pay attention, though, that the sustain does not fail 100% of the times when a buffer fails. In the tens if not hundreds of boards that we've serviced I can recall two cases where we had both buffers burn, but the sustain still working.

Just a reminder that nothing that we say is set in stone :-)

Now, off to the other Y main sustain problems:


While it is bound to happen sooner or later for the same reason for which most of the plasma sustain boards designed and produced at this point in time.
People - both home DIY self-repairmen and professional technicians - often think the IC has failed when in fact it has not (it's only been a buffer failure, hehe!).

Fact: when main IC on Y SUSTAIN MAIN LJ92-01200A fails, it usually results in a blown fuse F5004.

This is the largest fuse on board located right next to the IC and above the power connector.

Another indication for the IC failure is a short between two groups of legs as shown below:


When it comes to problems this is one of the most versatile boards I've seen.
* Nearly all electrolytic capacitors bar the largest two can be seen swallowed and/or defected.
* Power stabilizers may fail, taking down other components along with them
* Output current amplifier FETs may fail (the ones under the smallest of all 3 heat sinks) possibly taking down other components along with them

Chances are I am missing some.

It's getting very late here and I think I'll stop now. I may write a follow-up or edit this article to present general conclusions.

But, in short, it helps to understand why we are asking for all three boards to move together, why most of the time we advise people to replace both buffer boards and why in the rare cases when at least one of them is working we spend a lot of time trying to educate them about the risks they're taking with replacing just one of the buffers.

Hope you understand.

And, if you're service technician, hope you link to this article!


Rick52768 said...

Our TV never had the lines, red dots or scrambled picture. It was working one minute,no picture or sound the next. Same D12V error and I can get sound if I unplug the Y main board. The question I have is it possible it is only the Y main board and can I check by unplugging the buffer boards. As with just the Y main board, with no buffer boards the unit still has the error light, no pic, no sound. Former bench tech on consumer goods but before plasma and lcd came out. I Work for the local government in Kentucky and repair budget is tight. Have a good but cheap source for all three boards if that is what it takes or to be safe. Thanks

Bobby Kolev said...

You do not have to have had red dots in order for a buffer to fail , nor for the sustain.

It is completely possible that only the Y has failed - it is rare, but it still happens.

Test both buffers with the test I've described earlier in the blog and if both fail then it is completely possible for the Y to be shorted on its own.

See if you have the short that this article talks about.

There are several other less common failures on the Y as well....but if TV refuses to power with Y on and without the buffers you can be pretty certain it's the Y you are looking at.

And still I recommend if you send it for repair to send it along with the buffers. It is in your best interest.

Unknown said...

DELL W4201C 42IN Plasma TV
Sympton: Top half of screen blacks out once the TV has been on for a while. Tapping the screen will make it go away, but only for it to return again. Do you know if i need to just replace the Y Sustain board or do to replace the buffers too?

Unknown 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!...

Bobby Kolev said...

The answer to this question is in the article itself.

Unknown said...

i have a vizio p50hdm ,and right now i dont have sound or video.

y-sus 6870qyc004c
z-sus 6870qzc004b

i did few tests based on the info found here.

what i did was:
1.z-sus power cable out,powers on and stays green
2.with all power cables connected (y and z board)
,power on,and stays on
3. with y-sus power cable out ,powers and stays on.

now i did few tests with unplug controller board(the wide video plug-the one from y-sus to controller board)

4.y-sus power cable out-power stays on
5.all boards y and s boards connected-power stays on
6.z-sus power cable out-power stays on.

so now i am lost,i can figure out what board is bad.
anyone have a clue?
thank you.

Unknown said...
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Unknown said...
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Unknown said...

Hi,I have Fuji PDS5004E-S and pictures so pour.Anybody can help,where can I find the fault(Ic,resisitor,fet ..ecetra....)and how can I fix it repair?
Thank the

Unknown said...

I have a Magnavox 42MF230a/237 with the same y-sus and buffers mentioned in this and earlier article.
My buffers tested bad. I cannot read the -190 vdc VScan (it jumps around wildly) on the power board while cable connected to the y-sus board. With the cable disconnected it reads fine. No apparent bad caps on any board.

My Y-sus board has a good IC by indication of your test reference. I have 2 very hot resistors (R5098 & R5099). I assume the bad buffers are causing this but am unsure if maybe I have other bad components under the closest heatsink causing this.

Without disclosing too much competitive information, could you tell me whether the Y-sus is definately toasted or if I will toast it by powering it on without the buffers connected. Thanks for the excellent info you have already given me! More Thanks for any more you could provide!

Bobby Kolev said...

You can run any plasma TV without YSUS buffers. There'll be no picture, of course, but there is no risk to the YSUS.

In this particular case, if you have a shorted buffer you most likely also have a shorted YSUS so trying to run it will likely cause the TV to shut itself off.

Tye said...
This comment has been removed by the author.
Tye said...

I have these buffers in my tv.upper confirmed bad. After removing them I still had no voltage on vscan. The voltage no longer fluctuates just stays 0. Also similar symptoms to log with the hot resistors. After removing the connector to the logic board, vsync returns at -180 v and the resistors loose their heat. Does this indicate the logic board is bad? Any response/ hint would be helpful.

Unknown said...

if i remove the buffers my tv set stay on (green led), no blown fuses or apparent damage to parts in YSUS, it mean my YSUS board is good?

any help will be apreciated.

best regards.

Jay said...

With my ph-42t7 it has been working great for almost 4 years and all of a sudden starting this week periodically the bottom half of the screen had no display when turned on but after a minute or so it comes on.

any help is much appreciated.

Unknown said...

Thank you for this great information, it's been a tremendous help.

Have you any experience putting different buffer boards in the 3-board systems? The upper/lower buffer boards are running about $160 total, but this single-board is only $50!

It looks like the connectors are the same, but they're slightly offset... I could likely rig something with point-to-point soldering, assuming the signals are the same... (I'll verify the pinout when I order it...)

Another question: Have you ever seen a plasma with an undulating red blob in the center of the screen? It undulates outward almost filling the full screen. There're a few random blue and green pixels. It's almost like it's not receiving enough power for the whole display... but there's nothing recognizable in the blob, either. Could that be a failure in the Z-sus? Voltages seem correct, and I don't see any blown capacitors... but I couldn't get a whole lot of testing in before my Y-buffers shorted and took out yet another of the 7 parallel FETs in the Y-sus board.

Also, a note about your site: When you comment-as a Google account, it refreshes the screen with one of those text images ("Captcha"?)... but the form is cut-off by the adds at the bottom of the screen!

Robert Zenon said...

Just so you know I did have the red soreckles and the horizontal lines. I really knew that the Plasma was going bad, just did not know what was causing it. I Once it was down I open it it and checked for the problem and I soon found it was the lower buffer had failed one of the ICs had shorted. I started looking for replacements on the net and came across your Repair shop and Blog. Very intersting, it isn't rocket science. My set was a 42" Plasma I brought from Dell, I like the styling of the set and would like to restore it back to working order, so I will be ordering from you guys soon.

Unknown said...

Hi, i need your help.
please can you tell me that the UF and Volt of the next capacitors?

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