LED retrofit

[mathog]

When displays go it is usually either:

1. the power supply (especially the caps)
2. the inverter
3. the bulbs

For the first one swapping out the caps makes the most sense, but for 2,3 I'm beginning to wonder if at some point it may not make more sense to retrofit LEDs than to repair the CCFL electronics/bulbs. Companies are starting to make kits for this, for instance:

http://www.lcdparts.net/XB_Industrial.aspx

and there are sources for strips of surface mounted LEDs, example:

http://www.ledwholesalers.com/store/...ewCat&catId=66
http://www.lilyleds.com/productdetai...&categoryid=57

These are still fairly expensive though. The one thing I have not found yet is a source for the LEDs that are going into displays now. These seem to all be traded within China between various OEMs with no place to buy them directly.

Basically the repair I am imagining would be something like:

1. cut inverter out of the circuit (in some displays, this would be just removing a separate board.)
2. fool the logic into thinking the inverter was still there (there is usually a feed back loop of some sort, and if this isn't done the power supply will shut down.)
3. wire the LEDs directly to the power supply (match voltage of strip to whatever LED supplies).

The main problem would be that there would be no control of the brightness. The XB kit may (or may not) address that since it has a replacement board that goes in where the inverter was in a laptop. For a desktop retrofit there would need to be a little circuit added to convert the brightness voltage (on one pin into the inverter) into, most likely, a duty cycle change on a FET driving the LEDs. For models with a separate inverter there would be space for it where the inverter came out. For models with single board PS/inverter it isn't clear where this piece would fit.

Thoughts? Anybody here done this? Google for "LED display retrofit" and there are a few pages around for some home grown attempts at this.

[retiredcaps]

Re: LED retrofit

Thoughts?

If you want to learn, then it would be a worthwhile project.

From an economic point of view, I see that my local big fox sells a 20 inch widescreen LED for $99. That comes with a warranty and with the right credit card, I can get another year.

[mathog]

Re: LED retrofit

From an economic point of view, I see that my local big fox sells a 20 inch widescreen LED for $99. That comes with a warranty and with the right credit card, I can get another year.

Sure, most electronics are like that - makes more economic sense to toss them than to fix them. The biggest exception has been fixing small numbers of bad caps on various devices: $5-10 of caps and the device is as good as new. Replacement CCFL tubes are not as easy to come by, nor as inexpensive. Ditto for inverters, unless it is something simple, like a blown transistor or two. In those cases once the repair price approaches the price of buying a new one, the economics are wrong, although you might still want to fix it just for fun.

[retiredcaps]

Re: LED retrofit

Don't get me wrong, I would much rather repair/reuse than buy brand new. Most of the things I have are purchased 2nd hand/used or repaired, but some things are too important to me to buy 2nd hand and/or I have no interest in repairing them due to economic/time reasons. For the latter cases, I either resell or recycle them to others who can make use of them.

All my lcd monitors at home are repair jobs with 5 more waiting for some sort of repair. I started with lcd repairs by replacing bad caps, but now I'm finding SMPS repair to be more useful as almost all things have one.

Good luck in your project. I'm thinking that in about 2 to 3 years time, my local craigslist/kijiji will have more and more dead LED monitors for sale/free.

[tom66]

Re: LED retrofit

I've retrofitted LEDs into a 15" LCD monitor. I built my own board to drive them when the monitor turned on and used a power resistor to drop the internal 18V bus to 12V for the LEDs. The LEDs were rated for a 12V supply and had in-built resistors on a nice flexible tape. The total cost was less than £10.

[Scenic]

Re: LED retrofit

LED controllers (as inverter substitues) are available. Just not common yet.
http://cgi.ebay.com/280788607887

That seller also sells universal LCD controllers and touchscreen stuff.
For example this one, which might come in handy if you get a LCD monitor with a toasted mainboard, but everything else working (like my Samsung 223BW)
http://cgi.ebay.com/270885418490

[mathog]

Re: LED retrofit

I've retrofitted LEDs into a 15" LCD monitor. I built my own board to drive them when the monitor turned on and used a power resistor to drop the internal 18V bus to 12V for the LEDs. The LEDs were rated for a 12V supply and had in-built resistors on a nice flexible tape. The total cost was less than £10.

Pictures? Source for the LED tape?

Scenic's links were interesting too. That universal controller now has me wondering what the standard is for connecting the panel logic to the controller. Most of the devices I have worked on have used the stiff flat shiny connectors, the ones that look like they are printed onto thick mylar. That controller has a jumper which suggests that there is a standard sort of wiring, but no further detail. 1/2 ch "LVDS" in 6/8 bits, whatever LVDS is. Oh, low voltage differential signaling, but that sounds more like a description of the output stage than the name of a standard.

[Scenic]

Re: LED retrofit

LVDS is what goes from the controller board to the panel. It's pretty standard stuff, but the connectors come in all sorts of shapes and sizes. That seller sells a bunch of different cables too.. you'll have to match it to the panel (-> panel datasheet)
http://stores.ebay.com/njytouch/Cabl...4.c0.m14&_vc=1

2 LED backlight strips. Top one is from a cracked 15.6" laptop LCD, bottom one from a 10.1" netbook one.
http://bambooz.pytalhost.net/badcaps/led-backlight.jpg

the top one has 1 ground and 6 positive traces, the smaller netbook one has 1 ground and 3 positive traces. I'm pretty sure a simplified version could be done with just 2 pins and a bunch of SMD LEDs on some sort of small PCB strip
(or multiple pieces joined together, seeing how large the gaps in between the LEDs are (especially in the netbook one))

[tom66]

Re: LED retrofit

Pictures? Source for the LED tape?

Sure: See this thread: https://www.badcaps.net/forum/showth...ht=dell&page=2

LEDs came from here: http://www.giantcod.co.uk/high-densi...-p-404319.html

Next time I will use slightly brighter LEDs. The monitor is about 10% dimmer than most CCFL monitors. I could also reduce the resistor size and pump more current through them.

There's a rippling effect near the top of the screen. If I glued the LEDs in properly this wouldn't be a problem.

The resistor gets hot inside the monitor, so it's pressed against a metal heatsink to help keep it cool, but it operates within half of its rating so I don't expect failure any time soon. A buck converter would be a better choice for a later version.

The LEDs use considerably less power than the CCFLs and inverter. When unplugged, the monitor lasts for a good 2-3 seconds with no power, before it only lasted about 0.2 seconds, so the bulk capacitor is taking much longer to discharge...

[Scenic]

Re: LED retrofit

I just noticed I f*cked up in my previous post..

The white LED strip at the top is from the netbook (wide LED spacing) and has the 3 positive connections, the bottm one with the white text if from the 15.6" laptop LCD with 6 positive connections.. not vice versa.

The AMS1085CT is just as a size comparison (standard TO-220)

Another thing is that the netbook LED strip puts the light out at the top (much like the LED strips tom66 used), while the 15.6" notebook one has side-LEDs, i.e. it would be mounted on the side-wall of a CCFL tray, not the bottom.

[mathog]

Re: LED retrofit

LEDs came from here: http://www.giantcod.co.uk/high-densi...-p-404319.html

Giant cod???

Prices for these LED strips are all over the map, this is about the least expensive per length that I have found:

http://www.amazon.com/NEEWER%C2%AE-I.../dp/B005ONEJ00

Hard to find real specs on most of these sites. Not much point in replacing CCFL's with LEDs that are only rated for 10K hours. Googled for
"SMD 3528 specification" and the first link



on page 13 had a table showing intensity and percent of parts still working after so many hours, let's see if I can format that for this forum:

[FONT="Courier New"]
Time (kHours)     0   1   5  10  20  40  60  80  100
(intensity cd)
Current=10mA    1.168 1.158 1.132 1.088 1.040 1.004 0.988 0.936 0.879
Current=20mA    1.142 1.119 1.086 1.053 1.019 0.971 0.938 0.881 0.824
(working units %)
Current=10mA     100 99.17 96.92 93.10 88.99 85.97 84.62 80.10 75.27
Current=20mA     100 97.97 95.09 92.25 89.21 85.04 82.17 77.13 72.15
[/FONT]

So it looks like there are going to be dead LEDs showing up fairly quickly, but with most of them still working out to 100k hours. Makes me wonder what the display looks like as individual LEDs go out. When 25% have failed it might not be that bad if they were evenly spaced, but statistically there are going to be runs of bad ones, so there might well be dim spots on the screen.

[tom66]

Re: LED retrofit

Giant cod???

I used them on my model aircraft / flying wing as well.

These are power LEDs, operated at about 400mA each. With a 3V drop that corresponds to 1.2W. They barely get warm after 20 minutes of flying, but they are air cooled...