Heljan O Gauge Class 31 Diesel with Zimo Sound

Kit: MX699KS; 2x YLR302815; Cab Light SMD LEDs; Crew

Heljan's 2020 release of the Class 31 diesel looks lovely. Be careful handling and transporting though - there are a lot of bits that tend to be fragile.

Shown below is the model with the decoder and pair of speakers that we intend to fit...

The factory PCB, like most big Heljan diesels, must be removed and the wires transferred across to the decoder.

The fan control PCB can be removed altogether, as the decoder will be connected directly, using a 5V common, and a little extra dimming on the output to bring it down to a sensible spinning speed.

We add SMD white LEDs to each cab too, which will be controlled on their own fkey output. The LED wires are glued in a route across and then down, as we want to put the speakers in the centre, stuck to the bulk-heads.

The lugs on the YLR302815 speakers are trimmed for neatness, though probably not strictly required.

Using some BlackTack, we mount the speakers facing inwards with BlackTack on the 2 joining surfaces.

We begin the wiring up process, with pickups, motor and speakers (in parallel) first.

For the lighting, we need to protect the LEDs, so we've used a neat little PCB from Lais which has a bank of surface-mount resistors.

Front headcode goes to F0Fwd, rear headcode to F0Rev, front reds to FA1, rear reds to FA2. FA3 we leave for the fan control. FA4 and FA5 we use for front and rear cab lights. If you want to follow the same scheme, you'll need a few CV changes compared to our default template for the CL31 - you can request these when you order the decoder.

Once all the lighting wires are in place, we can tidy the bird's nest underneath the decoder - lots of room there.

The final steps are to wire in the connections that are in the loco body i.e. headcode lights and fan. The model also has lighting on the instrument panels in the cabs - this is very dim, but we have connected them together with the cab lights.

Time to reassemble and test everything again.

The completed model in its' splendor at the Swindon works...

Please note that these guides are provided as useful resources for you, as-is. YouChoos cannot be held responsible for errors in the information, or for any damage caused to your models or equipment if you choose to follow any of the steps detailed here.