Tuesday, October 7, 2014

LJ92-01490A repair question again

Question: 
 Dear Coppell TV Repair,

Just a question.
I have one of these sustain boards LJ92-01490A which was shorted.when I got the tv.
Both buffers were also shorted.
I bought a y sustain kit which consisted of all the transistors and diodes and three mosfets.
The tv would now turn on and stay on with no buffers attached.
Had all the right voltages.
I bought a used buffer on eBay and turned on the set and it immediately blew on of the buffer chips.
I have ordered two buffers and I guess my question is will the sustain if its on and working blow a buffer board or did I just get a ready to blow buffer.
My intentions are to send you all three boards to check but of course I would rather save the money.
I really am relying on your trustworthiness to tell me if a working sustain can blow a buffer board.
Thanks Gary

Answer:
OK, if you rely on our trustworthiness then read this carefully a few times because it may be somewhat confusing, but that's unfortunately how it is...it is complex.

1) A perfectly working YSUS board LJ92-01490A *can* and is known to sometimes damage perfectly working buffers.
In order for that to happen it will have to be fed improper signals by the plasma display controller.
A perfectly good YSUS, when fed proper signals, won't damage buffers, of course.

And of course the same is more or less valid for other plasma TV sets, but we've seen it happen with this one a bit more often than with others.


2) An improperly repaired YSUS LJ92-01490A *can* kill perfectly good buffers, even when fed proper signals from the plasma controller.

Knowing this particular board very well and knowing the SJ repair kit contents I am keen on making a statistically educated guess that some 20% to 30% of their customers for the kit would have an issue similar to yours. 




They just lack components in that kit that do tend to fail and when they do and don't get replaced they do cause exactly what you describe.

Of course there's no way for me to tell whether this is your case or if you have a bad plasma display controller or if you have yet another problem.

But I'll get to the question of what those components are a little further down.


3) I do not have an easy check for you on how you can test the plasma controller; it fails relatively rarely, but when it does it can very quickly turn a repair job into a financial cliff. I know that first hand.
So whenever I have the slightest doubt that it may be behind failures I tell customers - and would have told you if you've send us such boards - to have it replaced.
I have doubts based on the condition of the YSUS board when I first see it and the failures on it; in your case I can't do that, but if indeed BOTH buffer boards have failed I'd rather go for it.

4) While you can send all 3 boards you must be aware that we will not take them under our eBay listing as the YSUS has been worked on.


We'd only take it directly and we'd still offer no warranty. Only a video of it working in a set.


5) In the hundreds - yes, hundreds! - of LJ92-01490A boards we've serviced we've established that often times the problem is NOT on the board itself, but in how it was serviced before us.
There are several common mistakes people do when attempting to service that board and while I won't list here all of them for reasons I'll discuss in a minute I'll mention that one common problem is that people often tear the copper connection linking the top and bottom tracks on the board when they pull out the Vg filter capacitor (680 uF/25V or 35V -forgot which one) located near the power connector.

That leads to a board producing no image, which is not your problem, but illustrates my point.

In conclusion I'd like to say a few things.

First, no offense to SJ, but it is my opinion that a lot of their kits are simply sucked out of their fingers or, more likely, copied from other places. They are NOT based on first hand experience.
Of course that also allows them to have much more kits than companies like us who actually only release repair kits based on first hand experience.
Business-wise they are the smart people and we are the stupid ones.

Second, the above is also the explanation on why we do not want to disclose everything we know about repairing boards.

I personally stay late at night to reverse engineer, experiment, kill, repair and kill again a board before figuring out why it doesn't work the way it should.

I do not feel it fair - or reasonable - to post all of my findings only so companies like SJ or any coastal part distribution company can assemble a repair kit and start selling at a lower cost.

The value of what we do is in the knowledge we produce and the way we produce it - through hard work.

Of course, often times it gets out there, one way or another; but you'd be surprised how often it gets there incorrectly or partially (like with their repair kit).

Third, some issues are just too complicated to explain and fall under too many different cases to bother creating different repair kits and explaining which is for what; especially in the light of the risk of someone just copying the explanation and underpricing you.
Yet another argument is that a one-size-fits-all repair kit like the one SJ offers (for this case) is inefficient price-wise.
Their kit contains parts that you usually do not need, like the RJH3047 MOSFETs, which rarely fail, but it lacks other parts which you MUST replace when they fail.
Yet it contains 4 pieces 88N30W (or 88N30P), which you rarely ever need since they fail as a result of overload and it is worth to replace just the one or two that failed and not all four.


A universal repair kit would be highly expensive and highly inefficient, even when properly done. By "properly" I mean covering some 95% of all cases.

It would require reading and understanding and for those who manage to get through it the kit alone would become useless as they'd know which parts they need for what cases.

SJ apparently doesn't think so and , business-wise, they may be right and I may be wrong.

But that's how I am and that is how this company is run.

1 comments:

David Colglazier said...

I have purchased parts from you and had an technical exchange too which I found extremely helpful about determining whether a capacitor was defective even when it showed no signs - bulging or leaks...use a hair dryer to heat it up. I shared that knowledge on several sites and have been told my information helped well over 50 people...it was one 470uF cap on a main board that kept it from booting. I totally agree with you about efficiency in kitting parts when the buyer has reasonable knowledge of testing semi-s of all sorts. I personally don't have hardly any experience with MOSFETs because my hard knocks degree before these were in common usage even though I sold them for Signetics when they first came out in the 1970s. Your company is set up to help people, train some of them, train your staff to be efficient with only replacing defective parts and that will help your customers probably more than it helps you...I have a mechanic with exactly the same ethic and trust him totally as I do you. I suggest you look at kitting from both angles - 1) knowledgeable repair people don't need all the parts you provide and probably won't use all of them if they care to take the time to test every one before they get out the iron. 2) inexperienced repair people, maybe a larger percentage than you think, just want to get out the iron and put in all of the parts provided and have it work since they have no need or desire to educate themselves on the reasons things fail and how to test them. IMHO, you are better than your "competitors" who try to under price you while providing no additional hidden value of repair experience. But because of their pricing, they will always lure in more business than you can even though you and I know who should be rewarded by more orders...it's just human nature. When I provided a repair service for furniture especially antiques, I took the attitude that we're in business for those who will pay our prices to keep us in business...we're not in business for those seeking the lowest pricing even though I regretfully find myself in that group when I'm looking online for things. I can only conclude that because of this blog and our exchanges, I find you very open and honest about the problems both in repair and dealing with folks. That's the challenge and it eventually drove me away from my retail hardware business. Here's the one that made me put up the by appointment only sign...A local came into my retail store front in a tourist trap town and said she wanted to buy 8 drawer handles for an old dresser. After about 30 minutes of showing her handles that would fit the period of her piece I asked her why she wanted to replace them. She told me one of the eyebolts that held the bails was broken. I told her I had a replacement part for around $1 that would save her the $80+ she was going to spend thus saving her a substantial amount of money...her response was to complain about the high cost of that single $1 eyebolt and it was my only retail sale of that day...and I was making $30/hr doing repairs in the back. Should I have kept my mouth shut and sold her what she didn't need? Nough said! Dave orgood@iaxs.net

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