Fujitsu P20-2 finalized CCFL to LED conversion (#P9F1)

Canned content, for when I’m busy with stuff that’s not definite yet.

A while back, I tried the CCFL to LED conversion on one of my Fujitsu 20″ monitors. I only had warm white LED strips available at the time, mostly because I no longer require cold white DO STUDY NOW atmosphere at home ;) However piss-yellow doesn’t really shine behind an LCD, so I ordered some cold whites. AliExpress -> “2018 New 1m 1200LEDS 2835 SMD LED Strip 24V 1900lm 240LED/M Gold Line LED Ribbon LED Tape Light Cool White Warm White Natura”. 6000K color, 12V, “14-18W”. At a whopping 4.18€ including shipping, which is quite a lot for just one meter of LEDs. However, that’s reasonable given the high density and the CRI80+ rating (well, if that is true).

These are almost square 2835 LEDs, which does help a lot with even light distribution. Have a look – old generic ones:

And those 240 LED/m 2835 units: (a few are oddly placed and haven’t lined up during soldering. Thanks, lead-free crap!)

Here’s how they compare against each other, both at 12V (nominal voltage), where the cold white one is not just more suitable for a display backlight in terms of color, but also in brightness:

Well, let’s rip everything apart once again and get this thing done. Make two strips that fit on top and bottom:

Mash them in and seal with hot snot:

Next: The power supply. As mentioned in the previous blog post, the Mean Well RD50-A is an excellent fit. It offers 6A at 5V plus a second channel with 2A at 12V. So this powers the logic stuff as well as the backlight without the need for additional conversion, and it fits. Well, it’s a tight fit:

As the main back lid is entirely from metal and the heat sinks of the power supply are grounded (trap for young players!), I decided to take off the case from the power supply and run in that way. I don’t see any disadvantage at all, except for the need of keeping the case in a separate box for future re-use. The ground connection of the heat sinks is not just coincidence, there’s a screw connecting the case to it, so that’s a (good) design choice.

Some drilled holes and fiddly setup later, it’s finally in place:

One crappy dual Molex adapter later and the backlight is connected, all the 5V internals had cables available from last time:

Quick power up: It works! However, it doesn’t work 100%, but I didn’t realize at the time. There’s a couple of lines damaged at the very right edge of the screen, not sure if that’s a permanent thing due to hotbar damage of if that can be re-seated. I only noticed when everything was done and I’m too lazy to have a look. After all, this is a backup display and it will still serve its purpose with a couple of green pixels. But this is where I fucked up… :evil:

Now for the power stuff, as the power supply does not only need a sturdy internal mount, but also permanent wiring. Grabbed from the parts bin, 100% recycled components:

Fitted to the existing back lid – while that’s easy for the switch, it’s a bit more fiddly for the AC socket.

Hot snot time… :mrgreen:

And some more! AC is connected with two more Wago clamps, there’s shrinking tube, more hot snot and I think a hidden cable tie somewhere. Everything held in place, put the lid on, and we’re good to go!

Now let’s do some comparisons! Left one is the LED converted display, right one is on original CCFL configuration. I didn’t do color correction for these images as that’s going to be a mess due to different color temperatures, but these images capture reality pretty nicely. I think I had the camera on auto white balance, I’ll come to that later. Both monitors were set to factory defaults prior and were run like half an hour, so the CCFL one is at steady state. Test image from the always helpful lagom.nl. So white 254 is basically the same on both (as is black 1):

Colors are, I’d say, a bit more flashy than with the CCFL – that can be an advantage, but it doesn’t have to be. If you’re on sRGB or any other color space that requires some (hardware?) calibration, that new look will be pretty off. However, as the P20 allows for manual color space settings, that can be recalibrated in hardware and software and could improve total gamut of this old device.

Here’s the column driver damage :cry: and also a comparison of color temperature / white balance. This time, both displays sort-of look white.

When moving over to the LED screen, that’ll stay as it is…

…but when the CCFL screen gains presence, the white balance of the camera significantly auto-adjusts, for the worse. Look at the yellow-brownish part of the left screen.

What’s the color spectrum, then? Here’s the CCFL with clearly visible bands in the red (610ish nm) and green (550ish nm) parts of the spectrum. Surprisingly, there are two blue bands, one sharp one at 440ish nm (core blue) and another broader one at 490ish nm (turquoise). Both have a background band, and there’s also something in the orange region, but that’s not a primary color. The scale is about 10nm off if I recall correctly.

For comparison, this is the LED data: Huge share of blue, disappointing holes at 530nm and 580nm, and a little bit of everything in between.

Does that fit the spectrum data claimed by the AE seller?

Well, the 460nm blue peak is spot on, but I’d strongly disagree about the 590nm orange part (“dominant wave 580nm, my ass!) that would make this a well balanced spectrum. Rip-off as this is not CRI80+? Likely. But the population and therefore power density is there, and all I needed was this one meter of LED strip. And as we’ve seen from the comparison shots, even this spectrum leads to a more flashy image on this very screen compared to the probably heavily aged CCFLs.

Would I do that conversion again? Probably not.
Was it worth the time and money spent? Likely not.
Would I recommend this to others? Surely not.
Was it fun and educational? You bet!

The old display is now no longer with me, saving a bit of my space and helping others. And the new one is set aside, for when shit hits the fan, or strange things happen with VGA-only devices that could be hard to convert to HDMI. But that’s another blog post right there…


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