I'd never fitted a sound decoder before, but a purchase from Ebay found me the owner of a 21 pin ESU Lok sound decoder and speaker, complete with a WD 2-8-0 sound file on it. Therefore, the choice of model for my first attempt at fitting a sound decoder was already made for me, it had to be my Bachmann W/D 2-8-0. However, as it was a non DCC ready loco, it involved a little more than just plugging it in. So I bought a 21 pin socket and blanking plate for it too.

I always like to make as few drastic modifications to a model as possible. So after close inspection of the loco itself and studying it's service sheet, it became clear that the best place for the socket, decoder and speaker would be in the tender as there is so much more room in there than in the loco itself. To make the electrical connection between the loco and tender a little easier, I decided to fit a standard Hornby 4 pin plug in the loco and socket in the tender.

The first task was to dismantle the locomotive, however, before this was done, I tested and made notes of the wiring polarity, so it could be maintained after all the subsequent modifications. The small PCB fitted above the motor with capacitors and inductors was removed and discarded. I also removed and discarded all the wires from the pick-ups to the motor. The Hornby plug came with 4 long black wires, so I drilled 2 small holes in the plastic chassis keeper plate, close together, just in front of the brake cylinder which is located below the cab footplate. They were drilled so that they broke through just above the horizontal part of the keeper plate, they were then joined together to form an oval just large enough for the four wires to pass through.

2 views of the hole drilled into the keeper plate. (Sorry about the quality of the photos).

This enables 2 of the wires to pass directly to the pick-ups, and the other 2 to the motor using the original route for motor wires, and thus negating any modifications to the metal chassis, and are almost invisible when viewed from the normal viewing distance. I then soldered the 2 centre wires to the pick-ups and the 2 outer wires to the motor terminals, ensuring that I had the same polarity as that tested at the start. Once happy, the loco chassis was re-assembled and tested to ensure that it worked on DC before I went any further.

So that I could test the loco, without having to connect it to the tender, I made 2 small U shaped links, think mini staples, (see photo) just big enough to short 2 pins together, an outer pin to it's adjacent inner pin of the 4 pin plug, these links were fitted and the loco was placed on my rolling road, and powered up.

Close up of the home made shorting links

Links fitted into plug, note how they both face in different directions, to prevent short circuits.

Success, it worked correctly first time. So with all the modifying work on the locomotive complete and working successfully, I made the final modification to the loco, which was to shorten the drawbar. My thoughts then turned towards modifying the tender, but that'll be the subject of my next blog.