A very simple how to showing what needs to be done to upgrade the Cateye 3 LED front and rear bike lights to 5 LEDs.
Step 1: Tools and parts
You will need:
Soldering Iron Stand
2x 5mm red LEDs (5000mCd seem about the right brightness)
Small coin (to open case)
Step 2: Open the case
Insert the coin in the recess at the end of the case and twist. Once you have opened the case, remove the gasket so you don't loose it.
Step 3: Remove the PCB
This is the only hard part... removing the PCB without damaging it. The PCB is not attached to the case. It may look like it is, but it isn't. The only bits holding it in place are the battery contacts. Pull the battery contacts out using the long nose pliers. Only use moderate force, as the PCB will come out with them. Start at the end that doesn't have the switch. The negative battery terminal is the harder of the two to get out, so be careful. You will bend them a bit, but they bend back OK.
Step 4: Solder in the LEDs
Place the LEDs into the PCB making sure to put them in the same way round as the existing LEDs (they only work one way round). Then solder them in place. I find it easiest to solder one leg in place, then bend the LED into the correct position and then solder the other leg.
Step 5: Test
The testing is best done with a bench PSU set to 3V and a pair of croc clips. If you don't have a bench PSU, you can still test the PCB using the original AAA batteries, but it's just a lot more fiddly holding them in place. You may as well skip this and test the PCB once it's back in the case - but I would recommend double and triple checking that you have put the LEDs in the same way round as the original three!
Step 6: Finish
Put the batteries in, the gasket back on and the cover. All done! :D
The process is exactly the same for the Cateye HL130 front light too, except that you need white LEDs and not red ones. Enjoy.