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Another catch-up post.

A few weeks ago, I accepted my first order for a T43 backlight kit. It turned out to be a c-c-c-c-c-combo-breaker!

In the early days of software-controlled brightness, ThinkPads used an analog brightness signal like just about every notebook. It was generated by one of the D-to-A pins on the embedded Renesas H8S microntroller all ThinkPads used.

As of the X40, ThinkPads went to using a digital PWM brightness control generated by the Intel Centrino ICH Southbridge. This made them kind of weird by laptop standards. It's one of the reasons I had to cons up custom LED drivers for my ThinkPad brightness kits.

In general, the T and X series of the same generation shared a basic architecture. The planars were quite different, but the chipset and basic design were the same. Not so with the T4X and X4X.

The X40-series is a completely different design from the T40-series. It uses a PWM brightness control. The T40, however, is analog like the older machines, which threw me for a loop at first. The good news is that I'd made working drivers for the X2x, X3x, T2x and T3x beforehand, so once I realized the T4x was an 'old' style, getting it to work wasn't hard. I can use the same positive-analog TLD2 hack that worked on the earlier models.

The bad news is all my fabrication, based on the TLD3, is geared toward the PWM-based ThinkPads. The TLD3 boards aren't able to use a positive-analog brightness signal no matter the hack. For a TLD3, it's PWM input or nothing.

I have on hand ~ 1500 TLD3 PCBs, waiting to be populated, for the usual PWM kits. I have only ~ 20 TLD2 PCBs left that can be pressed into analog use.

Get 'em while you can.

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Packaging of the Chinese backlight kits I used to order tended to be... disappointing. Parts arrived broken on a regular basis, and there was never any moisture or static protection.

As a result, I put a little effort into my packaging.

With a paper cutter and an impulse sealer, it's easy to make moisture and ESD-proof bags of any size. The little table around the sealer was a quick afternoon toss-together made of MDF and a quick layer of paint. It locks into the lip along the bottom.

And of course, I make my own boxes! ThinkPad modders have taken to calling them Toblerones, which is kind of obvious, really.

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The ThinkPad LED backlight kits consist of two major pieces; an LED strip and an LED driver. The driver boards are designed to fit onto existing CCFL inverter boards after removing the CCFL step-up coil.

For good measure, I pull off the CCFL driver chip as well. Simply disabling it doesn't keep it from drawing a [very small] amount of current.

Removing the driver chip also opens up additional possibilities for reusing traces on the existing PCB. I don't like running long wires across the width of the inverter when hooking up the LED driver board. They'd need to be glued down to avoid accidental snagging, and that's a complication I don't need.

Instead, I re-route power, ground and the ENA and DIM signals through the original board, using solder bridges and 0-ohm bridge resistors where possible. On most boards, one or two jumpers are still needed, though a few boards I can get away without using any.

This work is most definitely all done under the microscope.

That also reminds me-- I need to get my library of reference modification pictures up somewhere.

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The first step is admitting you have a problem...

The problem being, specifically, that this stuff does not come in gallon cans.

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The LED strips are the big reason I still pick-and-place everything by hand. My tolerances here are just a few mils, and I've machined myself steel-and-aluminum templates to make the placement easier.

The idea is actually to place with looser tolerances, dropping the LEDs into the trough where the strip is clamped the check spacing and orientation with the microscope before reflow.

During reflow I tighten the guides on the jig and level the LEDs using a little precision squeegee I made out of aluminum and high-temp silicone.

Once the strip cools, I can pull it out of the jig, remove excess solder beads under the microscope, check for obvious defects, test on a power supply, and wash down with flux remover. Then it's on to applying the teflon layer, soldering pigtails, an up-to-temperature burn-in and flex test, and finally packaging.

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Initial functional testing of the LED drivers is just to find obvious reflow defects, mostly solder-bridges and non-obvious tombstoning.

Read more... )

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I'm currently on rev 3 of my ThinkPad-specific LED retrofit driver boards. They fit into the space on a stock inverter freed up by removing the CCFL step-up coil.

I'm on pace to make about 200-300 kits this year, and I'm still making them all by hand. Solder paste applied using a pneumatic dropper, components placed using tweezers and stereo microscope, then reflowed using a hotplate (thus the little placement jigs with silicone handles).

more after the cut... )

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LEDs and LED strip PCBs are finally here!

So now it's time to catch up with the LED backlight kit orders, aka, I know where all my free time is going the next few weeks...

(Does anyone else still remember the Dunkin' "Time to make the donuts" commercials?)

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First, the big if belated news: I'm now selling complete kits for T-series machines from the T20 through T500, as well as the W500. Oh, and let's not forget the T70. I do need to update the kits webpage to reflect all the new models.

This adds to the X-series kits I already offer for the X20 through the CCFL versions of the X200. And yes, the X62 as well.

That said, I'm waiting on an order of LEDs from Nichia. My most recent order collided badly with the beginning of Golden Week, so the arrival ETA is around May 30th. I won't be able to build new kits until then, and the buyers queue is currently about a week deep.

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Since I love LEDs and I love meters, it is totally obvious to put LEDs into meters.

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spoiler: Nichia Rocks. But first a flashback.

Remember those crazy Chinese LEDs I was looking for? They had kind of iffy construction, but up to that point they were the closest color match I could find to what I needed for my Thinkpad backlight project. I found more of the same type from random Chinese resellers, but none with exacly the same whitepoint as the original. I never determined the manufacturer.

I was looking for these dodgy Chinese LEDs because I couldn't get any major manufacturers or resellers to sell me the LEDs I needed in any kind of reasonable quantity. The smallest amount any factory quoted was a MOQ of 100,000 and that was only because a friend of a friend was willing to call in a favor to an unnamed factory in Hebei. The name brands you'd recognize weren't willing to discuss anything less than 1,000,000 units.

Or so I thought. I'd stopped looking slightly too early.

The AFFS LCDs I'm retrofitting have red and green filters with a lot of overlap in the yellow region because the original CCFL backlight doesn't put out much yellow. The broad yellow peak from typical white LEDs pollutes the red and green primaries. That messes up the saturation and color reproduction, even if the white point is correct.

But last year Nichia released a new line of component phosphor LEDs specifically designed for backlighting that don't use a broad yellow phosphor; they use separate red and green phosphors.

The specs also claimed tight binning, surprisingly high lumens/watt, and a weirdly low forward voltage. Oh, and they came in a low-profile 3014 package rated for mid-power output.

With no great optimism, I called up Nichia USA and asked for some samples. After being redirected a few times, I talked to a nice lady in Detroit who was happy to send me some LEDs for testing. That was farther than I expected to get.

The LED samples were everything the specs claimed them to be. I had never tested an LED as efficient, or with color binning so tight. They blew everything else out of the water.

So I called back. "What was the minimum order?" The answer: 1 reel, only 5,000 LEDs. Too good to be true.

The next question I was sure would undo me: "Can you tell me if I order now, what kind of bin I'll get?" I was still expecting to get something in the rough ballpark of what I really wanted that I could then tweak a bit with a filter. The reply: "What do you mean? You can have any bin mentioned on the spec sheet."

I could select specific whitepoint, forward voltage, and luminosity bin. At only 5,000 quantity. Jaw on floor.

It still felt too good to be true, but Nichia made the LEDs on-demand in Japan when I placed the order, and they arrived in the mail 15 calendar days later.

So as it turns out, I was able to get my dream LED for this silly little custom project. I'm reminded to post this now as there's been steady demand for the resulting Thinkpad backlight retrofit kits, and it's time to order another reel.

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There are so many posts that need to come out of this one...

I ordered a whole bunch of Chinese LED conversion kits. I tried lots of ways to mod them to work on Thinkpads, all of which worked... though many turn out not to work well enough, so don't use the mods on those pages for now :-(

Dissatisfied with all offerings, I designed and have been testing my own LED driver boards....

The LED strips that came with the Chinese kits all had terrible color rendering (low temperature, greenish, or both) on the spiffy AFFS screens the X61T is known for.

...so that's sucked me into the world of spectrometers, reverse engineering the protocols to use them on Linux (oh, yeah, I need to publish that), binning leds by hand with a makeshift integration chamber...

...and then of course all the software needed to take the SPD data from the assembled system and interpret the color data, then plot it, which I just finished today!

That contrast measurement is too low and I know why, the sensor is too close and unbaffled, so it's picking up IPS glow. Time for measurement jig rev 2....

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In case anyone was wondering what I was doing with all the LEDs recently, I've been converting classic Thinkpads with old, dying CCFL backlights to LED. It's a popular mod, and there are plenty of generic DIY backlight kits out there. Unfortunately, most of these kits don't work as-is, and there are no good instructions, walkthroughs, reviews or comparisons of various kits anyway.

I've just had a great deal of fun fixing that. Consider this a beta-test invitation :-)

Also... I touched the white tape. I touched it really quite a lot.

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I've been working on a backlight retrofit project with some odd and fairly tight spectral output requirements. Specifically, I need a cool-white LED with a very low CIE Y value. Something around x=.3 y=.28 resulting in a purplish/pinkish tinge.

As luck would have it, one of the first engineering samples I ordered from <insert random Chinese Supplier here> as part of a larger kit nailed the requirement perfectly. What luck! I ordered an additional large lot of exactly the same part--- and was sent completely different LEDs the second time around. The combination of language barrier and reluctance to name their own suppliers has meant I've made no progress on tracking more of these suckers down. I have 50. I need about 2000.

Large photomicrographs under the cut )


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