Installing a decoder into a Hornby Class A1 Terrier 0-6-0 Tank Loco

Click on each image for a more detailed view.


Before installing DCC chips into any loco it is advisable to check the current being drawn by the loco.

This loco is NOT DCC ready so you will need to do some soldering. You will also need a small philips screwdriver and two pieces of 2.5mm heatshrink.

Space is at a premium inside this loco - a small decoder will be required, in this case a TCS M1 decoder was used but you could, for example, also use a Zimo MX622, NCE Z14SR or Digitrax DZ125.


A1X body removal step 1

To remove the body there are two philips type screws that need to be undone, one at the front and one at the back. Once the screws have been removed the body can lifted from the chassis.

A1X weight removal

There are one or two possible alternative strategies for installing a decoder in this loco, so the method used below is just one suggestion.

It was decided that most space was available in the bunker, out of view. The bunker contains one of the two weights in the loco (the other is in the boiler). In general I am not in favour of removing weights - if they are there then they are there for a reason! So, although the weight is going to be removed, part of it will be put back.

To gain access to the weight it is necessary to remove the two screws shown in the photo and then detach the cab from the loco by GENTLY releasing the 3 lugs indicated. The two at the sides are easy to release, the one at the rear less so, so be very careful whilst handling the loco that some of the delicate detail is not damaged and that the body is not split by the bufferbeam.

Weight in A1X Decoder installed

Remove the weight and cut along the lines shown on the left hand photo. The shaped piece of weight that fits at the very back was then superglued back into place.

A hole was drilled through the base of the cab where there is a small protrusion in the plastic moulding. This matches a similar protrusion on the main body and a similar hole should be drilled here through which the decoder wires can be routed.

The decoder had the white, yellow and blue wires cut back as these will not be required for this installation, the loco not having any lights or smoke unit. It was then placed sideways into the available slot in the bunker moulding.

The second piece of weight was then placed into the available space. The TCS M1 is ideal for this type of installation as it is already insulated. If you are using a different make of decoder it is essential to ensure that it is insulated before you reassemble the model.

A1X ready to reassemble body

A1X body reassembled

Pass the decoder wires through the hole that has been drilled in the cab.

Now pass the wires through the hole that has been made in the body and reassemble the body, relocating the lugs on the cab into the available slots in the main body.

A1X Chassis

It is now necessary to desolder the three wires (red, yellow and black) from the capacitor, and to desolder the capacitor from the motor terminals. There are three wires each side of the loco, one for the pickup on each wheel.

Now cut back the orange and grey wires from the decoder to a reasonable length and solder to the motor terminals, orange to the right side, grey to the left. (It doesn't matter too much if you get this the wrong way round as adjustments can be made to the decoder once installed to ensure the loco runs in the right direction. Just make sure that the red wire from the decoder is linked to the pickups on the same side as the orange wire!)

Solder together the red and yellow wires on the right side of the loco and slide a piece of heatshrink tubing over the two wires and away from the join and the heat (otherwise the tubing will shrink where you don't want it to!!). Now solder the black wire on the right hand side with the red wire from the decoder and join these to the yellow/red wires already connected. Slide the heat-shrink over the join and heat it to shrink and secure the join in place.

Repeat the process with wires from the left hand side, connecting red and yellow from the pickups, slide the other piece of heat shrink over the two wires, then solder the black pickup wire to the black wire from the decoder and join together.

5MT body

Test the setup before replacing the body. You can also do any programming of the decoder at this point, but it might be better to replace the body first to ensure all is still working before you alter any CVs.

Please note that the picture alongside actually shows the body the wrong way round for mounting on to the chassis! Wiring is correct, though!!


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