Author Topic: EEVBlog #465 - LED LCD panel teardown  (Read 18536 times)

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Offline tom66

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EEVBlog #465 - LED LCD panel teardown
« on: April 30, 2013, 11:25:10 pm »


Interesting video.

That diode looks to be VGL or VGH boost gen. These voltages are used to select or deselect TFT rows. If that diode went bad, the panel probably became really dim or brownish in colour, or blurry. So I'm guessing that they replaced it due to that fault. And that would have been -really- easy to fix!

Chi Mei panels are made by Chi Mei. They're a Taiwanese company that bought out some of Samsung's smaller panel business, hence some of their earlier panels are basically Samsung panels, but the newer ones are mostly different. They have a plant or a few in China.

I don't like Chi Mei panels much. A lot of them have failures due to tab bonds. They're one of the cheaper panels available, but they aren't very nice to watch. Lots of motion blur, poor contrast ratio, poor colour rendering and accuracy. And they have a lot of mura problems in their earlier panels due to backlight overheating.

That one chip on the T-con board (the board attached to the back of the panel) is basically doing everything that's needed today for LCD panels -- it's taking the input LVDS, converting the format, and sending it out to each TAB driver (eight drivers, 5760 subpixels, 720 channels per IC at 15V each... remember R,G,B are separate pixels. Pretty impressive semiconductor design...!) The tab drivers are fairly dumb. They're basically 960 channels of 4-bit DAC (0-15V output), shift registers with LVDS input. 4 bits isn't enough to drive 8 bits of course, so the gamma IC is used to interpolate the TFT's curve to give a linear response. There's 16 levels on each 4-bit DAC of course and usually 12 or 16 channels of gamma (common to the whole panel), giving 192 or 256 levels. Additional levels are gained through time-multiplexed dithering algorithms, but due to the small T-con IC... I'd doubt it's doing that. It's probably a full 8 bit panel.
« Last Edit: April 30, 2013, 11:31:30 pm by tom66 »
 

Offline robbak

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #1 on: April 30, 2013, 11:40:47 pm »
Those driver chips: are they raw silicon bonded on to the flex cable and backfilled with epoxy - basically, chip-on-board stuff with a little more sophistication?
 

Offline tom66

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #2 on: April 30, 2013, 11:44:10 pm »
Those driver chips: are they raw silicon bonded on to the flex cable and backfilled with epoxy - basically, chip-on-board stuff with a little more sophistication?

From my research they are sold as bare dies. I have a feeling since Novatek appears on the ribbons, that they are Novatek driver ICs.
http://www.novatek.com.tw/products/Flatpanel.asp

I guess Chi-Mei buys them in. Samsung, LG, Sharp, Panasonic (IPS Alpha) etc. I think all make their own as they have good fab capacity, Chi Mei is a relatively small company which hasn't been around for very long.
 

Offline Ketturi

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #3 on: April 30, 2013, 11:53:25 pm »
I once took apart one of those LED lighted panels, all leds were in series, and driving voltage were like freaking 80V. More common pattern is 4 or 8 etc. in series and each parallel. Nice big supply for high efficiency leds with pretty good white color, though I would make little art installation with those, if i have time to de&resolder them.

Those films are very nice construction material, and older LCD:s have usually more thicker lightguide, 1cm or so. If sanded or sand blown, those could be useful for frontpanels maybe?
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Offline EEVblog

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #4 on: May 01, 2013, 12:04:59 am »
Those driver chips: are they raw silicon bonded on to the flex cable and backfilled with epoxy - basically, chip-on-board stuff with a little more sophistication?

Probably bare die bonded to the flex and then capped/epoxied. Any know for sure?
 

Offline Ax_6

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #5 on: May 01, 2013, 12:15:55 am »
If anyone know where to buy those diffusers would be awesome
 

Offline PeteInTexas

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #6 on: May 01, 2013, 03:26:59 am »
Why are the LED rectangular?  I would have thought square or round would be optimal.
 

Offline nkinnan

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #7 on: May 01, 2013, 04:07:41 am »
On a couple of the zoom shots, where you can see the individual sub-pixels, it looked like there were tiny little packaged devices attached to the ribbon in line with each row/col.  They even had numbers etched onto them.  I thought the transistors were etched into the glass, are those miniscule resistors or something?  Are there actual packaged devices this small that are individually placed by a machine? 

Edit: here's what I'm talking about, its apparently "attached" to the post but I'm new to this board and I don't know if I can reference it as an IMG tag.  Is this just an etched pattern or something (circled in red)?
« Last Edit: May 01, 2013, 05:10:55 am by nkinnan »
 

Offline andyturk

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #8 on: May 01, 2013, 04:40:39 am »
Regarding the fully routed board thing...

I was on an assembly factory tour last week where they produced small boards that were routed all the way around. The PCB panels that went into the pick and place had multiple boards joined with the usual connecting tabs. After the entire panel was assembled, it went into a special router machine with a custom aluminum (aluminium?) plate below that matched the 3D profile of the entire panel.

A 1mm router bit went around CNC-style and removed the tabs while a vacuum on the lower plate sucked all the debris down and away. It took 5-10 seconds per panel to break out the entire set of boards, which had no dust whatsoever. The vacuum on the lower plate not only sucked out the routing debris, but also kept the individual boards from moving as the last few tabs were cut.
 

Offline Corporate666

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #9 on: May 01, 2013, 05:24:59 am »
Dave,

When you are done with the panel, save the diffusion sheet - it is *fantastic* for making lights for video/photography softer.   It diffuses with little loss... I've tried to buy that stuff before and it's very very expensive too!
It's not always the most popular person who gets the job done.
 

Offline almoehi

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #10 on: May 01, 2013, 07:18:58 am »
Wow! That was one of the most interesting tear downs, in my eyes. Thanks Dave.

:-+

Cheers
Armin
 

Offline nitro2k01

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #11 on: May 01, 2013, 07:20:57 am »
Looking at the video, I saw what looks like a small defect in one of the test pads. Some missing copper. Or actually a huge defect, if that's what it is. If it was placed over the traces, it would blank out several rows.
Whoa! How the hell did Dave know that Bob is my uncle? Amazing!
 

Offline amyk

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #12 on: May 01, 2013, 07:51:27 am »
One thing I've wondered is whether an existing CCFL panel could be made to run on LEDs by using a long series string of them since the inverter is a current source providing several mA... although you'd need a couple hundred and in antiparallel since the output is AC.
From my research they are sold as bare dies. I have a feeling since Novatek appears on the ribbons, that they are Novatek driver ICs.
http://www.novatek.com.tw/products/Flatpanel.asp
Actually they're sold bonded to the flex already; that's the NT39962H-C5107A and NT39512H-C5105A in the panel Dave tore down. Unfortunately Novatek datasheets are near-unobtanium (although there's nothing particularly special about these chips) so I couldn't find those exact parts, but here are the datasheets for a similar set:

NT3980 384-channel 8-bit source driver
NT39207 480-channel gate driver
Good intro to how they work

The pitch on the traces probably matches the bump spacing on the die: 50?m. That's approximately half the pitch of the pixels themselves. (Note that LCD driver IC manufacturers refer to as pixels what we'd normally call subpixels, so to them this is a 5760-wide display and not 1920.)

I doubt the interesting patterns are test pads; might be some sort of decoupling capacitor(?) Ditto for the odd looping traces... which remind me of an RFID tag.
« Last Edit: May 01, 2013, 08:00:08 am by amyk »
 

Offline mckillnm

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #13 on: May 01, 2013, 07:58:17 am »
Hi Dave!

Great video (as always!).. Here is another good video on LCD monitors with a good description of the optics:


-Mark
 

Offline od-lambda

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #14 on: May 01, 2013, 09:26:35 am »
Hey!!!!!

I take more time ago one blog to lcd led and see parts in microscope,

Like see my simple blog:

www.od-lambda.com

I lioe this video show more parts!!!


Thanks!!!
 

Offline nitro2k01

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #15 on: May 01, 2013, 11:16:13 am »
od-lambda: I was wondering if you posted the wrong link or something, because of the intro animation covered the whole screen and no way to skip it. It's just annoying. Remove it, please!
Also, maybe you want to post a direct link to the post. If someone reads your post in 5 years, the LCD post may no longer be the latest post.

http://www.od-lambda.com/2012/12/analisis-de-la-tecnologia-lcd-led.html

But nice microscope images.
Whoa! How the hell did Dave know that Bob is my uncle? Amazing!
 

Offline Memphis

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #16 on: May 01, 2013, 11:25:32 am »
:) nice shots with RGB filters. BTW at 1:30 in Daves video the resistors are actually in parallel to differential channels. They looks like 100R LVDS termination  8) a like how they solve it with an resistor array.
...sorry for my english :palm:
 

Offline ondreji

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #17 on: May 01, 2013, 12:13:30 pm »
White board can't be used as white balance as is: you should use 18% grey board. Camera tries to average everything to 18% grey. Hence your white board will be grey -- you need to adjust exposure by two stops up and then set WB.
 

Offline free_electron

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #18 on: May 01, 2013, 01:59:19 pm »
There's two ways to mount those chips. They are either csbga . Essentially a naked chip where the top layer is copper and solder balls are applied.
This is the old technology.

As number of connections went up the balls would be too small.
So now we use copper pillars. These are plated with an enepig (nickel palladium gold) process.
The chips are then friction welded . Backfill provides the mechanical strength.
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Offline jrag

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #19 on: May 01, 2013, 03:29:05 pm »
Some time ago I made a white light frame (like the ones doctors use to see through Xrays photos films) with a broken laptop LCD.
I have taken out only the pixel glass panel and replaced it with a clear 2mm thick glass (cost me around 1.5 euro or 2 dollars), leaving all the light diffusing layers. It’s really bright, I use it to align the holes in dual layer PCBs to use with the toner transfer method.

Basically you align the two toner printed sides, I use some thin white magazine like paper, put some duct tape in one side to fix the alignment, and then slide the dual copper sided virgin PCB in between. The next thing is to put this paper-PCB-paper sandwich in a laminator or press it with a clothes iron. Personally I use a hacked laminator, the hack was to change the thermostat to a higher temperature, like 150º Celsius (3 dollars on ebay). After that the paper is stuck to the PCB, you just put it in water, scrub the paper and the toner will all be in the PCB, and then ETCH IT.

My panel was illuminated with CFL though, but I had the inverter so no problem  8)
With LED LCDs its basically the same thing, you just need to drive them.

Mehh I've already post some of this on the comments but I decided to post this here too  :P
<8>
 

Offline nixxon

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #20 on: May 01, 2013, 04:31:17 pm »
Why are the LED rectangular?  I would have thought square or round would be optimal.

A group consisting of a Red, a Green and a Blue pixels makes a nice square.

Circles would leave pleny of useless voids in between the circles.
 

Offline cchalk

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #21 on: May 01, 2013, 04:46:44 pm »
I thought this was one of the most interesting tear downs I've seen in a long time.
Please, do another video about the light diffusion.

Thanks!
 

Offline free_electron

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #22 on: May 01, 2013, 07:32:47 pm »
those led's are rated at 80 to 90mA per led...
since you got 4 banks the the total drive current for half that block is in the order of 240 mA to 250mA ...
they will be extremely bright at that current
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Offline M0BSW

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #23 on: May 02, 2013, 02:18:32 pm »
 I had a old digital TV screen outside, it didn't have diodes , it had 8 long thin tubes, I've put them to one side as I thought they may make a  light source for a light box, for make circuit boards ???. I may try and wire them up to a old fluorescent tube choke and see what happens . good tear down made me final rob the thing and get rid of some rubbish at the same time, there was also several sheets some frosted, a white one, thought I could draw circuits or what to do list on that with those markers you can rub off, there's a silver one in there to. anyway really enjoyed the tear down good one Dave, oh the screen was Sony.
« Last Edit: May 02, 2013, 04:29:24 pm by M0BSW »
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Offline cjones

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #24 on: May 02, 2013, 03:55:17 pm »
I work as a technician with smaller (mostly 6") tft screens and all our drivers are chip on glass. It works very nicely but does require a larger glass sheet. Maybe it would be too large with that number of lines to drive.

Dave, do you have any lasers? I think that would be a fun way to visualize what the various diffusion layers are doing.
 

Offline tom66

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #25 on: May 02, 2013, 08:24:15 pm »
If you hook CCFLs to a flouroscent tube ballast, the result will be an explosion of glass from the CFL.
 

Offline M0BSW

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #26 on: May 03, 2013, 06:16:37 am »
 I won't be doing that then, perhaps no point in keeping them.
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Offline SeanB

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #27 on: May 03, 2013, 03:02:48 pm »
They will work on battery powered inverters though, like the ones you get in camping lanterns.
 

Offline M0BSW

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #28 on: May 05, 2013, 09:31:52 am »
They will work on battery powered inverters though, like the ones you get in camping lanterns.
That's a nice idea sean, something to play with on a rainy day. cheers
Paul
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Offline SeanB

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #29 on: May 05, 2013, 09:37:02 am »
Any lamp inverter that has a sinlge wire to the lamp will drive them, or you can use the power blocks for EL wire as well.
 

Offline amyk

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #30 on: May 05, 2013, 10:13:51 am »
Inverters are also sold with CCFLs intended for PC case lighting (no idea why anyone would want to add EMI next to their sensitive electronics...)
http://www.amazon.com/12-Cold-Cathode-Case-Lights/dp/B000BUDHOA/
 

Offline Dexmind

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #31 on: August 12, 2018, 03:42:51 pm »
Thanks for the video.i learn a lot from that :) .
I have problem if someone can help.i cracked my screen wire trace inside glass.how i fix connect again that wire? Where location i can do jumper wire? Thanks a lot before :D
 

Offline jakeisprobably

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Re: EEVBlog #465 - LED LCD panel teardown
« Reply #32 on: February 08, 2019, 08:33:43 pm »
What is the purpose of these trace shapes and routing?
(From the video ar 23:11)
 


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