Author Topic: Repair guide  (Read 7029 times)

mmicsa

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Repair guide
« on: April 28, 2013, 06:35:30 PM »
Hi guys.

mjlorton suggested I post on the forum because fixing things is not his forte, so here goes, maybe together we can fix my board.
I scrapped an LG W2252TQ monitor that has the following problem.
After it turns on, it then quickly turns off.
The same is happening if I adjust the resolution.
It's clearly the power inverter, but since it's on the power board, I need your help to fix it.
Attached are some pics, and I already marked the caps I changed ... just to be safe :) (picture here: https://dl.dropboxusercontent.com/u/7125910/Up.jpg , for some reason it did nou upload, sorry guys)
So, ant of you have any ideas of what to test next ?
Maybe I can make a video and other folks out.
Thank you in advance for your help.

Marius.
« Last Edit: April 28, 2013, 06:37:20 PM by mmicsa »

retiredcaps

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Re: Repair guide
« Reply #1 on: April 28, 2013, 07:34:20 PM »
See if you have "2 seconds to black".  Start with post 19 at

http://www.badcaps.net/forum/showthread.php?t=10419

mmicsa

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Re: Repair guide
« Reply #2 on: April 30, 2013, 05:41:39 PM »
Hi.

Just to clear any confusion, here is a video of the monitor in action: http://www.youtube.com/watch?feature=player_detailpage&v=wrXKGnfSDE8

In addition, I am hearing a high pitched sound coming from the board, but I have not yet had the time to see where it comes from.
I still have a few caps I want to change just in case and if it still fails to run, i'll check further.
In the meantime, I tested all diodes I could see, they-re fine, I tested a few resistors (randomly) they all checked out.
On the page retiredcaps suggested I found a LOT of info but some of it is confusing.
I tried to test the Inverter Transformer but I am uncertain if the values I read were good or bad.
And also, the page mentioned picofuses I have yet to find.
Anyway, I will post an update as soon as I make some progress.
In the meantime, please feel free to post any ideas you guys have.
Thank you for your help.
« Last Edit: April 30, 2013, 05:48:18 PM by mmicsa »

retiredcaps

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Re: Repair guide
« Reply #3 on: May 01, 2013, 01:11:11 AM »
Just to clear any confusion, here is a video of the monitor in action: http://www.youtube.com/watch?feature=player_detailpage&v=wrXKGnfSDE8
I always recommend hooking up a source (i.e. computer) with your favourite wallpaper to verify, but it sure does look like 2 seconds to black.

Quote
In addition, I am hearing a high pitched sound coming from the board, but I have not yet had the time to see where it comes from.
That could be arcing on the ccfl connectors?

Quote
I tried to test the Inverter Transformer but I am uncertain if the values I read were good or bad.
Post the readings of your transformers.  A clear focused picture of front would help and the part number of the transformer.

mmicsa

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Re: Repair guide
« Reply #4 on: May 01, 2013, 04:25:24 AM »
Hi

Picture of the inverter transformer attached. (not the one on the PCB but identical)
On the forum you suggested I found a series of YouTube videos that were quite helpful: https://www.youtube.com/playlist?list=PLd8dosDlv_aqB4CwsbDcFK9eYEsDtCVe9
I actually got it running after watching this video: https://www.youtube.com/watch?v=D4exxfE9lf4&list=PLd8dosDlv_aqB4CwsbDcFK9eYEsDtCVe9
But, I consider this a temporary solution and I still want to find the actual fault, not just bypass it.
I will post pics of the transformer values tonight (we are observing a national holiday in RO so it's barbecue time right now)
FYI, do I need to take it out, or is it fine if just measure in circuit ?
Thank you.

retiredcaps

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Re: Repair guide
« Reply #5 on: May 01, 2013, 05:23:43 PM »
I actually got it running after watching this video: https://www.youtube.com/watch?v=D4exxfE9lf4&list=PLd8dosDlv_aqB4CwsbDcFK9eYEsDtCVe9
Those videos are made by tom66 who is a regular on badcaps.net and eevblog.com.

Quote
FYI, do I need to take it out, or is it fine if just measure in circuit ?
You can do the measurements in circuit.  Obviously, power off and unplug the lcd to do resistance measurements. 

See

http://lcdparts.net/TransformerDetail3D.aspx?ProductID=3697

Measure the resistance between S1-S2 and S3-S4.  You should get around 960 ohms for reach.  Report your findings.

mmicsa

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Re: Repair guide
« Reply #6 on: May 03, 2013, 03:56:48 PM »
Hi guys.

So, I measured the transformer and got:

S1-S2: 930 Ohm
S3-S4: 1266 Ohm
P1-P2: 0.2 Ohm (=/- , my multimeter does not go below 200 Ohm)
I tested all pins on the primary, they all have between 01 and 02 Ohms

S3 and S4 ar being used for lower lamps, so I am a bit concerned about not reading 930 Ohm.
Also, using tom66's fix does turn on the monitor but the lower half is noticeably darker, so I am guessing the lights are either not turned on, or at least one of them is off.
Have we found the problem ?

retiredcaps

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Re: Repair guide
« Reply #7 on: May 03, 2013, 07:04:06 PM »
S1-S2: 930 Ohm
S3-S4: 1266 Ohm
The S3-S4 resistance reading suggests the windings are bad (3% out of specification).

Replacements are available on ebay for about $12 USD + free shipping).

mmicsa

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Re: Repair guide
« Reply #8 on: May 07, 2013, 06:04:15 AM »
Hi guys,

Just a short status update.
I have taken the transformer out, retested, and confirmed that it's off spec. (930 and 18xx)
I am waiting now for a test transformer from one of my mates and I will be testing the CCFL-s.
If they turn out to be good (fingers crossed) I will replace the transformer and hope to restore full functionality.
If not, well, we'll keep digging  :P

mmicsa

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Re: Repair guide
« Reply #9 on: June 11, 2013, 01:55:49 PM »
Hi guys.

Sorry for the long delay, but I've been busy.
Anyway, I got the transformer from eBay, changed it out and for a few minutes, everything seemed fine.
After a few minutes though, the screen just turned off and I was unable to power it on again for several minutes after it was disconnected from the power supply.
Even if I leave it turned off but plugged in, it will not turn on again.
Any ideas ? Or is it time to cut my losses and just replace the board ?
Thank you.

retiredcaps

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Re: Repair guide
« Reply #10 on: June 11, 2013, 06:09:34 PM »
Check the replacement transformer to make sure it is around 930 ohms and double check your soldering.

mmicsa

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Re: Repair guide
« Reply #11 on: June 12, 2013, 05:24:32 AM »
I checked the new transformer and is was spot on 930.
How dare you question my soldering  :P
I will take it apart again and check, but I don't think it's the soldering.
I can hear a high pitched noise coming from the power supply, I am thinking it's a transistor, although I remember checking them.
Well, I guess it;s back to the drawing board.

retiredcaps

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Re: Repair guide
« Reply #12 on: June 12, 2013, 05:05:38 PM »
If the monitor comes on and works for a few minutes, I suggest you record DC voltage measurements on the power board (connector cable to main board).  Also measure any voltage regulators on the main board.

Once the monitor goes off, record the same DC voltages and do a comparison.  That might give you a clue as to why the monitor is turning off.