This is a standard Kato electric locomotive dcc conversion. It has the old board with cooper tracks only in one side and there is no need of difficult modifications to this board. Using a tiny decoder, Doehler&Haas PD05A-3 in my case, there is no need of sanding and fits perfectly.
The only modification to the board are:
- Remove the capacitor in one side of the board. It will have no effect when leds are connected to the decoder
- Keep the positive lead of each led connected to the track feed by the central resistor. For this, leads of the left led must be swapped
- Do not solder or cut the negative lead of the led, as this will be connected to the white or yellow wires of the decoder.
First of all remember to isolate the cooper plates in the position were they are in contact with the motor plates. I use Kapton tape for this.
Then I placed the decoder in the center of the board with double sided tape. In this position, it fits exactly in the interior free space of the shell. Having the decoder in place, cut wires as shorter as possible and solder them to the right points as you can see in the photo.
There are no more things to explain, images are quite self-explanatory, if not, write in the comments any doubt.