EEVBlog #465 - LED LCD panel teardown - Page 1
Forum section: electronics / general

author: tom66
author_rank: Super Contributor
timestamp: April 30, 2013, 11:25:10 pm
content: 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.

author: robbak
author_rank: Contributor
timestamp: April 30, 2013, 11:40:47 pm
content: 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?

author: tom66
author_rank: Super Contributor
timestamp: April 30, 2013, 11:44:10 pm
content: Quote from: robbak on April 30, 2013, 11:40:47 pmFrom 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.aspI 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.

author: Ketturi
author_rank: Regular Contributor
timestamp: April 30, 2013, 11:53:25 pm
content: 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?

author: EEVblog
author_rank: Unknown
timestamp: May 01, 2013, 12:04:59 am
content: Quote from: robbak on April 30, 2013, 11:40:47 pmProbably bare die bonded to the flex and then capped/epoxied. Any know for sure?

author: Ax_6
author_rank: Contributor
timestamp: May 01, 2013, 12:15:55 am
content: If anyone know where to buy those diffusers would be awesome

author: PeteInTexas
author_rank: Frequent Contributor
timestamp: May 01, 2013, 03:26:59 am
content: Why are the LED rectangular? I would have thought square or round would be optimal.

author: nkinnan
author_rank: Newbie
timestamp: May 01, 2013, 04:07:41 am
content: 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)?

author: andyturk
author_rank: Frequent Contributor
timestamp: May 01, 2013, 04:40:39 am
content: 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.

author: Corporate666
author_rank: Unknown
timestamp: May 01, 2013, 05:24:59 am
content: 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!

author: almoehi
author_rank: Contributor
timestamp: May 01, 2013, 07:18:58 am
content: Wow! That was one of the most interesting tear downs, in my eyes. Thanks Dave.CheersArmin

author: nitro2k01
author_rank: Frequent Contributor
timestamp: May 01, 2013, 07:20:57 am
content: 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.

author: amyk
author_rank: Super Contributor
timestamp: May 01, 2013, 07:51:27 am
content: 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.Quote from: tom66 on April 30, 2013, 11:44:10 pmActually they're soldbonded 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 driverNT39207 480-channel gate driverGood intro to how they workThe 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.

author: mckillnm
author_rank: Newbie
timestamp: May 01, 2013, 07:58:17 am
content: Hi Dave!Great video (as always!).. Here is another good video on LCD monitors with a good description of the optics:-Mark

author: od-lambda
author_rank: Newbie
timestamp: May 01, 2013, 09:26:35 am
content: Hey!!!!!I take more time ago one blog to lcd led and see parts in microscope,Like see my simple blog:www.od-lambda.comI lioe this video show more parts!!!Thanks!!!

author: nitro2k01
author_rank: Frequent Contributor
timestamp: May 01, 2013, 11:16:13 am
content: 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.htmlBut nice microscope images.

author: Memphis
author_rank: Contributor
timestamp: May 01, 2013, 11:25:32 am
content: nice shots with RGB filters. BTW at 1:30 inDaves videothe resistors are actually in parallel to differential channels. They looks like 100R LVDS terminationa like how they solve it with an resistor array.

author: ondreji
author_rank: Contributor
timestamp: May 01, 2013, 12:13:30 pm
content: 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.

author: free_electron
author_rank: Super Contributor
timestamp: May 01, 2013, 01:59:19 pm
content: 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.

author: jrag
author_rank: Newbie
timestamp: May 01, 2013, 03:29:05 pm
content: 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 problemWith 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

author: nixxon
author_rank: Frequent Contributor
timestamp: May 01, 2013, 04:31:17 pm
content: Quote from: PeteInTexas on May 01, 2013, 03:26:59 amA 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.

author: cchalk
author_rank: Newbie
timestamp: May 01, 2013, 04:46:44 pm
content: 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!

author: free_electron
author_rank: Super Contributor
timestamp: May 01, 2013, 07:32:47 pm
content: 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

author: M0BSW
author_rank: Frequent Contributor
timestamp: May 02, 2013, 02:18:32 pm
content: 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.

author: cjones
author_rank: Newbie
timestamp: May 02, 2013, 03:55:17 pm
content: 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.

author: tom66
author_rank: Super Contributor
timestamp: May 02, 2013, 08:24:15 pm
content: If you hook CCFLs to a flouroscent tube ballast, the result will be an explosion of glass from the CFL.

author: M0BSW
author_rank: Frequent Contributor
timestamp: May 03, 2013, 06:16:37 am
content: I won't be doing that then, perhaps no point in keeping them.

author: SeanB
author_rank: Super Contributor
timestamp: May 03, 2013, 03:02:48 pm
content: They will work on battery powered inverters though, like the ones you get in camping lanterns.

author: M0BSW
author_rank: Frequent Contributor
timestamp: May 05, 2013, 09:31:52 am
content: Quote from: SeanB on May 03, 2013, 03:02:48 pmThat's a nice idea sean, something to play with on a rainy day. cheersPaul

author: SeanB
author_rank: Super Contributor
timestamp: May 05, 2013, 09:37:02 am
content: 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.

author: amyk
author_rank: Super Contributor
timestamp: May 05, 2013, 10:13:51 am
content: 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/

author: Dexmind
author_rank: Newbie
timestamp: August 12, 2018, 03:42:51 pm
content: Quote from: Dexmind on August 12, 2018, 03:07:53 pm

author: jakeisprobably
author_rank: Regular Contributor
timestamp: February 08, 2019, 08:33:43 pm
content: What is the purpose of these trace shapes and routing?(From the video ar 23:11)