Example 1 - Sound and firebox glow only, with speaker under chimney

Kit: MX648; SugarCube8; SMD Nano firebox LED

The Hornby OO M7, with DCC sound using a Zimo MX648 and firebox glow. The M7 is a pretty thing, but very short on space for treats! So we've got to do away with the DCC socket, to make room for the decoder or speaker. In fact, there isn't going to be enough room to get both the decoder (Zimo MX648) and speaker in the boiler, so we decide to put the decoder in the bunker.

Off with all the gubbins, socket, supression capacitor etc.

Grind the socket's screw mounts flat:

A SugarCube8 goes under the chimney, just about. It could sit upright like this, with some electrical tape between it and the chassis...

...but in fact, we choose to place the speaker the other way up, and stick it under the chimney like below. Just measuring the space at the moment, and refitting the body to ensure that it will be able to go back on flush when we're all done:

We're happy with the fit, so we add speaker wires, and stick the speaker into its' final position using a thick double-sided pad:

Since we don't have much room, we will totally remove the unwanted wires from the decoder (white, yellow and brown in this case). I have also replaced the orange, grey, red and black wires with much longer ones, as we need to run these up to the motor and pickups. We keep the green and blue though, as we want to add a firebox glow light... before and after wire removal (DO NOT do this unless you have good soldering skills and a decent fine-tipped soldering iron!!):

Cut out holes under the bunker floor for the decoder wires to go through - it is actually easier to remove the coal from the bunker and feed down from the top - you don't need holes as large as what I've made here! I've also routed trenches for the motor, pickup and speaker wires to sit in as they go forward, including a channel vertically up behind the smoke box - this will prevent the wires from getting pinched when we put the body back on later.

The firebox glow light is an orange SMD LED, glued onto the smoke box door. We can get away with this simple approach on a Tank engine, because the LED is not directly visible. Paint the white parts of the LED, and the wires black to help disguise them though, and feed the LED's wires through the floor, routing back to the bunker.

The firebox LED needs a resistor on the positive wire, before attaching to the decoder's blue wire. The LED's negative wire attaches to the decoder's green function wire. We've used heat-shrink to totally cover the resistor and electrical joins.

Stuff it all into the bunker, and chop the pivot legs from the coal moulding, as the coal will have to sit slightly higher than it previously did. In fact, once in, we'll glue on some lump coal to improve the look!

All in, tested, firebox glow on - beautiful!

Example 2 - Bigger speaker and SuperCap stay-alive

Kit: MX648; IceCube18X13X10-1W; LifeLink with SuperCap17000uF; SMD Nano firebox LED

Remove the 8pin DCC socket and flatten the platform under the chimney.

Test-fit the SuperCap 17000uF in the side tank, which looks to be a perfect fit.

Screw mounts from the DCC socket are milled down flat.

From the top of the bunker, remove all the plastic, leaving suppport for the retaining screw at the base. This is where our large IceCube speaker will go.

Purple speaker wires added.

MX648 has been rewired, removing unwanted lighting wires (white, yellow and brown), and adding GROUND wire for the stay-alive, then re-cover in Kapton tape.

Nano SMD firebox glow LED is glued into position in a hole made into the cab, and the wires channelled and protected with some electrical tape.

LifeLink PCB sits on top of the decoder.

YouChoos 3D Printed crew figures added, and weathering applied - lovely!

Example 3: MGOLANG stay-alive

Kit: MS480, SugarCube7, Nano Firebox Glow, LifeLink and MGOLANG stay-alive

Similar approach to the SuperCap plan, but this time using a Zimo MGOLANG stay-alive, which is 6 mini GoldCaps in a series-array. The overall height of the GoldCaps is marginally less than the SuperCap, so this fits a tiny bit better.

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.