We were a little surprised to discover that this 2017 re-release of Farish's GWR Diesel Railcar was still based on the old split-chassis model, with no
factory-provision for DCC, but it did run well and so made a good candidate for DCC conversion, starting with a standard (non-sound) decoder, hard-wiring a
The chassis block is huge (hence the good running), with the metal right up to the roof, so very little space for even a standard decoder.
Unpick the tape and we find that at least the motor terminals are separated from the chassis, so DCC conversion is a doddle, electrically.
Here is the MX617, which we shorten any wires not required (we will not attempt to fit any lighting).
Connect grey and orange decoder wires to the motor terminals, and black and red top the chassis halves.
The decoder is slightly too thick (with it's heat shrink still on) to fit in the roof so we simply snip off a small plastic lug that protrudes downwards
and it frees up just enough height. Very tight though. It might have been better to remove the heat shrink and replace this with Kapton Tape, but wanted
this exercise to be the minimum work required to DCC-fit it. The results are good - the model runs fantastically on DCC and was converted in just a few minutes.
So, now to convert the same model to DCC sound...
We need to create some space, both for a sound decoder and also for a speaker. Fortunately the chassis is a lump, so there are various options for removing
chunks! Take it all apart and mark out what we will grind away - some off the top for the decoder, and a chunk from the underneath for the speaker.
The blue speakers are Minnows, and the green one is a Limo6. We eventually decide on a Limo6.
Reassemble the chassis and test-fit the speaker. It will obviously need to be insulated properly from the chassis, but we can afford it to be very
slightly proud of the bottom because the body shell goes lower than the chassis base.
With shortened wires, removed unwanted lighting wires, and recovered with Kapton Tape, the MX648 decoder fits into the recess that we created
on top of the chassis, though we still have to create a little more space up into the roof.
With everything in place, we protect the speaker and disguise it with black tape, refit the body, and check that everything has enough
clearance from the rails.