What kind of LCD defect is this?

unixadm

Gawd
Joined
Jun 13, 2002
Messages
561
I bought a couple "B" grade U2711's to use as perimeter monitors in a 3xU2711 Eyefinity set up. My center display will be a brand new U2711 as I didn't want any defects, however for the outside monitors it was tolerable because they are not my primary focus.

The defects on both displays are in the exact same place. The defects are purple splotches or dots roughly 1/4" in diameter. On anything but a black background they are nearly impossible to see. I took a couple of pictures of these A03 revision U2711 displays. Both defects are at 50MM down from the top of the panel. Not sure if its a pressure defect or a de-lamination issue. The pixels themselves work and there are not suck pixels from what it looks like. I could understand panel defects but for two displays manufactured at different times to have the same defect in the same area seems to point to something other than the LCD panel itself. I don't know though. I work in IT and I have never seen an LCD since 2003 that had this type of defect.

I'm still perfectly happy with the displays considering the discount. My office is gonna be hot with four 27's though!

IMG_1115.JPG

IMG_1112.JPG

IMG_1113.JPG
 

Crest

Limp Gawd
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Oct 7, 2009
Messages
433
Did you try different inputs or cables?

Do they change if you touch them?
 

sadbuttrue

Gawd
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Feb 16, 2008
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I can't say what it is, but my first Dell 2209wa purchased 2 years ago had exactly the same problem. To me it appeared as tho something was pressing against the screen from behind. All replacements since have been fine (I've had a few for various issues).
 

jeremyshaw

[H]F Junkie
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Aug 26, 2009
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lol. I have held off from joining my U2711 with any others, until lower power LED (RGB, preferably) alternatives are on the market :p

Otherwise, one at anything above 10% brightness = hot.
 

munkle

[H]F Junkie
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Jan 16, 2005
Messages
11,800
lol. I have held off from joining my U2711 with any others, until lower power LED (RGB, preferably) alternatives are on the market :p

Otherwise, one at anything above 10% brightness = hot.

My 3008wfp put off more heat than my 46inch ccfl tv, used more power too. :p
 

Acer_Sheep

[H]ard|Gawd
Joined
May 18, 2007
Messages
1,201
If you would disassemble it and take a look on those places from behind you could fix it. Some layers inside LCD panel are just sticked to each other and probably on those it became worn off and separated from rest of the display, actually it look like more light from behind goes through those spots.
 

unixadm

Gawd
Joined
Jun 13, 2002
Messages
561
I'll pull one of them apart tomorrow and see if I can find anything. I do agree that it looks like like light bleed thru from behind the screen. Otherwise the two displays are working nicely.
 

unixadm

Gawd
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Jun 13, 2002
Messages
561
I disassembled one of the U2711 monitors today. It's not too bad, just a lot of wires, small parts, screws and clips to deal with.

My findings are that the LCD itself is fine. The issue is with the CCFL backlight diffuser panel. The U2711 has a vast array of U shaped CCFL bulbs. It seems one of the U shaped CCFL bulbs is defective and is bleeding light unevenly. They must have had a bad batch of CCFL diffuser panels. That explains the even 50MM from the top as that's right where one of the bulbs runs. Based on the amount of backlights in the diffuser panel, I could try to "guess" where the defects in the CCFL bulb are and cover them with a small piece of electrical tape. I think it would cause a very minor dark spot on the screen but based on how the diffuser works I think it would hardly be noticeable. I went ahead and reassembled the display to ensure I had the routine down and I'm using it right now to type this message.

It's a project I'll tackle another time as I will need very accurate measurements on the horizontal plane of where the defects are. It would be much easier if I could power the CCFL while dissembled but unfortunately I don't have the equipment to do that. If I could source a replacement CCFL bulb it probably would be a 90 minute job to replace it.

Overall it's not really worth the effort. I hardly notice the defects even when using the display as my primary monitor.

Actually it looks like I can buy a replacement U shaped CCFL bulbs for around $20 a piece - I'll probably go that route to replace the defect bulb in each display.
 
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AMoody

Limp Gawd
Joined
Feb 14, 2010
Messages
167
watch out for the backlighting power inverter when you are taking an LCD apart.

Also, make sure you get bulbs that are an exact match to avoid uniformity issues.
 

unixadm

Gawd
Joined
Jun 13, 2002
Messages
561
What I can do is swap in one replacement bulb and reassemble the display. If the back light is not uniform then I will replace all of the bulbs in one monitor and use the good pulls to fix the other. The other option is buying a CCFL bulb tester off eBay for around $50 and using that to power the bulbs and just block out the small defective area of the bulbs. Based on the number of bulbs and the diffuser panel, I doubt it would be detectable.
 

tk-don

Limp Gawd
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Jun 15, 2010
Messages
324
You would hate yourself if you end up replacing one of the CCFLs with one that differs slightly in spectrum, i.e. uses different phosphors. There are many combinations available.

Besides, i'm not sure i see why it has anything to do with the CCFL itself. Light clearly/distinctly escapes, and that shouldn't happen in the first place no matter what type of non-uniform output that CCFL had. As the points are so distinct i'd maybe try to source a cheap pair of polarized glasses (circularly polarized). Put them on, and see if the same points become black at a certain position, when the unaffected areas have blacked out. If these spots are unaffected, it is a defect with either the front or back polarizer. That would mean new panel.
 

unixadm

Gawd
Joined
Jun 13, 2002
Messages
561
Looking at the panel with polarized glasses yields no anomalies. The panel evenly blacks out under a variety of background colors. The spots do not show up inconsistently from the rest of the panel. So what does that mean?
 

nardox

n00b
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Oct 10, 2010
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My 3008wfp put off more heat than my 46inch ccfl tv, used more power too. :p

My KRP-500M plasma TV put off more heat than two of my friend's 3008wfp combined, I have to mount 3 low RPM fans behind the TV...:D
 
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