Step 1: Remove the old circuit board.
The board can go and join the others we removed from other projects.
Step 2: The new turbo circuit.
We will need to use 1/2W LED, which are readily available on eBay:
here, or here. They each have slightly different products, but I've used both and they're both reliable.
The real star of this circuit is the driver transistor, FJN965, from Fairchild Semi. Capable of handling up to 5-amps of current in a TO-92 case, it will start at .9v and run the light until the battery drops to under 0.3-volts. You can get them from http://fairchildsemi.com
Resistors, capacitors and inductors can be obtained from your local supply houses (eg Radio Shack, The Source), Sure Electronics, or at online surplus stores, like http://AllElectronics.com
The second image shows the layout using a Perfboard. S+ and S- indicate the wires from the Solar cell.