Thursday, July 2, 2015

Toshiba 42XV540U backlight and no image on screen repair

It's been a while since I blogged component level repair, so here's something.

A customer brought a Toshiba 42XV540U LCD TV after we've serviced the power supply PE0580A for him.

He said the TV started responding and clicking after our repair, but the display remained dark.

We agreed on returning the money for the board repair and taking the TV instead as he said he didn't want to invest more time with it.

So summarize:
TV model: Toshiba 42XV540U

Failure symptoms: TV responds to power on command, fans start turning and back light comes on (we could see from the back of the TV and a glow could be seen from the front, but only in a dark room).
We could not make the TV output sound by blindly trying to change inputs; if you know how to do it perhaps you can do it , thus eliminating the main board as a top suspect.

Solution:  The TV was responsive to on and off commands, which suggests the main board was good.
(failed main boards usually fail to do one or both of those operations). Plus backlight was coming up, which means the main board's processor was up and running to the point of activating the backlight.
On the other hand we couldn't get sound out of it.
We checked the voltage going to the T-CON board and it was there - 12V DC.

So the options were the main board (less likely), the T-CON or the video accelerator PE0578 (about equally likely) or the display itself (unlikely, it rarely ever fails to all dark screen).

Luckily it turned out we had eBay listings for both the T-CON and the accelerator board.

Testing with them it turned out the problem was in the accelerator board PE0578.

Knowing that we've put the bad and the good one side by side and started hunting:

Found the problem in the voltage stabilizer from 12V to 3.3V.
As you can see there was a significantly lower resistance there and, more importantly, it was the same in both directions on the bad board:

On the good board it was a good diode read - 0.5 - 0.6 kOhm in one direction and infinite or very high in the other:

(The measurement can be made on several points and there are several components there that could be causing it; there were a few inductors we removed in order to eliminate the circuits after that as well as a few diodes that were in parallel and could have been causing the shortage).

The only passive component we found to have been bad was diode  D592 on the back of the board. It was fairly well shorted, having about 4-5 Ohm in both directions:

Used generic diode for replacement, such as the ones used in our repair kits for BN44-00161A power supply. Almost any diode will likely do, including even zener diodes (assuming it's properly soldered in regards to its polarity, of course).

Long story short, we traced it down to the actual DC converter/stabilizer IC (AOZ1017AI).

But since we didn't have a replacement handy and our US vendor didn't have it either (had to ether use another US vendor or our Asian vendor), we took matter in our hands and just hacked a stabilizer of our own:

The solution worked out well and the TV is presently operational.

While I don't give out everything I hope this helps someone save a buck or two :-)

Good luck!

Thursday, June 25, 2015

Testing LJ92-01511A / PS-507-PHN for Philips 50PFP5332D plasma TV

A customer reported that a returned power supply LJ92-01511A for their 50'' Philips (or Magnavox, it's used in different models from both brands) is not producing Vs after it was serviced by us.

Before returning it to here we asked them to test the board independently as we do (that is, manually power on the board and instruct it to activate Vs) to see if it behaves as it did when it was here.

Customer said he tests the board by disconnecting the sustain boards from it and turning on the TV.

The problem with that approach is that if the main board OR the plasma logic board is bad the power supply may never get instructed to turn on Vs in the first place.

So we made this video to help test the board in standalone mode:

Of course like everything else choosing one alternative over another has its drawbacks too.

Testing without load like this is not an ultimate proof the board is functional since it may fail to operate when loaded. This does indeed happen sometimes, but in our experience it is rare enough to justify saving the overhead of a full blown test.

If a board behaves differently with and without a load then a more careful inspection under load is clearly needed.

And still more often than not the problem would turn out to be in the load and not the power supply - i.e. shorted sustain board in plasma TVs or main board in the LCD/LEDs.

Tuesday, April 14, 2015

Two different types of support conversation

After posting the email exchange with an eager wannabe-customer last week I got a few emails from alert readers.

Most showed agreement, some disagreement and the really good ones, in my opinion, said that right or wrong, it is silly of me to post such things on the web because Americans are raised to believe that customer is king and they see as a personal threat anyone who applies critical thinking to that belief.

I am not trying to start a revolution here.

Customer is a customer and without customers there will be business, but that does not mean that one has to take all the crap customers have to offer.

Here's two more email exchanges that happened during the course of the last evening:

From: Jeff Poole []
Sent: Monday, April 13, 2015 2:54 PM
To: Coppell TV Repair LLC
Subject: Coppell TV Repair. Contact us

Question 1.1: A friend gave me a Vizio P50 HDTV20A which he said the picture just went out on.  I opened up the tv and on what I believe is considered the Y-Main board there are two resistors or capacitors (I'm not electronically inclined) that are side by side nearest the Y -Buffer boards that are heating up and burning.  The circuit board around the leads on these components has turned brown and of course that god awful smell of burning circuit board was filling the room.  My question, is this something which can be repaired by your company?  What could be the root cause of these components heating up to the melting point?  Is this a lost cause?  I just want to see if the thing is repairable before I ship the boards to you.  If it would help I can take a picture of the board and the two components.  I would appreciate any guidance you can give me here.

Answer 1.1:
Which is the Y-Main board?

This model uses several very different ones.

Question 1.2:
I really appreciate you responding back to my question.  The board which I am seeing the two components that are heating up is located on the left side of the television if you are standing behind it.  From what I have read on your site and else where that is why I called this the Y main board but that terminology may not be correct.  Also, this board connects to the Y Buffer (?) boards on the left hand side of the television.  In the hopes that you can tell me whether this board is repairable I am attaching a picture of the board along with a close up of the two components that are heating up. My main concern is what would cause these components to heat up like this?  Is there something I can do to help you diagnose whether I need to ;send other boards?

Answer 1.2: 
99.9% certain your top buffer board is burned.
Your Y-Main board is most likely also affected and will need to be serviced.

Can’t say with certainty yet, but your most likely solution would be to have the buffer replaced and the Y-Main repaired.

Proper way to do it is to  have both top and bottom buffers replaced with brand new ones. That would be $180 and with Y-main repair at $70 it becomes too expensive for most people. But it’s the only proper way to repair it.
It’s expensive because Samsung has run out of buffer boards and does not seem to be producing new ones again.

The popular way now is to replace the top buffer with a serviced one for $70 and Y-main repair for another $70.

Search at our site for LJ92-01490A and LJ92-01491A and make sure to read both.

It is possible it may be worse than that, but this is the most common case.


Question 2.1:
From: Greg Gillum []
Sent: Monday, April 13, 2015 5:05 PM
To: Coppell TV Repair LLC
Subject: Re: Coppell TV Repair LLC: shipping instructions


Did you receive my order inquiry?

Greg Gillum

On Wed, Apr 8, 2015 at 6:58 PM, Coppell TV Repair wrote:
Dear Greg Gillum,
This message contains shipping instructions for your defective board(s) you wish us to service.
Please read carefully and do what we ask to ensure the best experience for both yourself and us.
a) Sender's email is
b) Sender's phone is 6------6.
c) Please initial your board(s) with a marker. It can help resolve a confusion here or in a video proof that the board is working (if and when applicable).
d) Your message to us is:
I have 2 toshiba LCD TVs that recently went bad after a lightning storm the other night. Model 46ux600u has no power whatsoever - its main fuse is intact and I can detect power at the capacitors. The power supply board does not seem to be available any longer. Model 47zv650u lights an LED when its plugged in then begins a repeating series of clicks as if its trying to turn on but never does. What do you suggest? Are these both likely power supply boards? I've not taken the back panel off the 47zv650u yet as I don't know what to look for anyway.

....reminder of our standard shipping instructions truncated....

Answer 2.1

Not sure what are you referring to.

Apparently we’ve received the service request, the below email is a proof of that.

Question 2.2


Yes, I asked a question in my request for service and I was waiting on a response. Do you have a moment to review my question and respond?
Answer 2.2

Yes, if you had bothered to read the text on the form you had filled to initiate a request you would have found this:

“Use this form to request shipping instructions for the modules you want to send to Coppell TV Repair for diagnostic and/or repair service.

The form will be sent to the supplied email address immediately and we kindly ask that you print and enclose it along with the boards you send to us.

Do NOT use this form to ask us questions! The information supplied will only be used upon receiving and servicing your modules.”

Three paragraphs aren’t too much to ask, are they?

That said I can’t really make much of a recommendation from here when the TVs are there.

Power surges enter through power supply and the main board (cable or antenna) and usually affect power supply board or main board.

We can test the power supplies, but I can’t promise you they would be the only bad thing in the TVs, if bad at all.

Question 2.3

Fuck you. Good luck with your business.


Guess if we do want that customer's business?

Answer: no, we do not. We do not anyone's business if they are not capable of following clear and simple instructions and operate based on their assumptions.

TV repair is not a rocket science, but is risky enough where one can cause enough damage on themselves and/or electronic modules and components.

People with low attention and low moral/language are a high risk for themselves and others and , as the example here shows, usually stand in their own way of properly resolving a problem.