This page describes installing a Lenz decoder into a RS-2 using the supplied light board as a substrate. This involves trimming the board at one end to allow room for the decoder, and cutting the traces such that the decoder leads can be attached appropriately. The original board has two LEDs and one dropping resistor. One of the LEDs is cut off, so it needs to be replaced with one with longer leads, and two dropping resistors have to be installed. Luckily there is room at one end of the board to mount these next to it. The cut traces disables the original dropping resistor, and I use that trace to transfer power from one resistor to the far LED. I exchanged the supplied LEDs with super bright whites (from Digikey, RS). The one thing I did wrong was attach the resistors a little too close to the frame clamps, so it is impossible to remove the board from the loco without unsoldering them. I think you could probably arrange them more aft, so removal would be possible. Good luck!
Comments: I don't guarantee this is accurate and you follow these instructions at your own risk. I will check it with the actual working prototype, but double check everything. Digitrax makes a drop-in decoder for the Kato RS-2, it is slightly more expensive than the Lenz, but I had bought 4 of these (they'll fit into a LifeLike SW9/1200!, see http://nietzsche.mit.edu/~auro/trains/tech/dcc.lifelike.sw9_1200/ ). - David
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