This is the Jornada.
First of all, we should get to the backlight. The cover was removed easily by un-screwing a pair of tiny Torx screws and wriggling the pieces of plastic cover apart with a screwdriver.
The CCFL as-is uses around 125mA. For your information: That's about half the power the PDA itself uses.
The CCFL itself is viewable by opening the metal casing of the display and folding out the reflective flap covering it.
Let's replace it by white leds. I decided to slice of a long piece of really thin PCB I had lying around somewhere.
The places where the LEDs go were then prepared with a knife.
To solder the white LEDs I first used a drop of glue to fix them to their positions. Then I soldered the gold connection points to the PCB. Take care to solder them all in the same direction; you don't want to desolder a led! What's the anode and what's the cathode usually is indicated by a T-shaped thingy at the bottom of the LED.
Testing the LEDs. My camera couldn't cope with the high contrasts, so you can't see the LEDs are brighter than the CCFL.
Folded in the reflective screen / diffuser plastic part of the LCD, you can see that the light of the white LEDs is distributed mostly homogenous.
And when the LEDs are placed in the display itself, you can see the image is visible quite well. Although the display in reality is a bit more blue than with the CCFL, this picture somehow exaggerates the effect.
This is the way I got the fourty volts needed to drive the white LEDs: 2 12V accus in series with my lab power supply. I could've used 9V batteries too, but I didn't have any around.
Next: The backlight controller. This was my first prototype: later the inductor and the capacitor turned out to have values that weren't ideal, so I replaced them by other components.
The firmware in development. The gray cable is the ISP cable used to program the ATTiny13.
And this is the hardware (it's still attached to it's programming cable here) I eventually ended up with. It uses about 90mA on the 7.4V rail, that's a reduction of about 1/3.
With duc[k|t]tape, everything stays in its place. The backlight controller is no exception.
And the result. The Jornada seems happy with it. Again: the camera unfortunately exaggerates certain effects, it looks much nicer and less blue in real life.