Bought a bike computer from Ebay, and found out it had absolutely horrible backlight.
So I cracked it open and found out that while the PCB had pads for two 3mm leds, only one was used, and it had a tiny board with an SMD led on it.
The plastic piece behind the screen had notches for 3mm leds, but they weren't actually cut out.
Cut the hole, added a white 3mm led and soldered a resistor.
I didn't actually remove the old led.
It's that very, very faint blue glowy dot on the right edge.
Yeah, I said it was crappy :P