Installing a DCC decoder in a Hornby Battle of Britain 4-6-2 Locomotive

These instructions apply to both the Hornby West Country and Merchant Navy classes of locos as

they use a similar mechanism, though there is less space inside the body of the Merchant Navy for a decoder.

Click on each image for a more detailed view.


BB on rolling road

Before installing chip into any loco it is advisable to check the current being drawn by the loco. This photo show a loco being run on a rolling road, with power being provided via a RRampMeter. You should test the current drawn when the loco is stalled to find the peak current and select a decoder that will cope with that maximum current requirement.

BB and decoder
The intention, with this installation, was to use a TCS T1 decoder, but space inside the loco, once the body had been removed, revealed less space than had been anticipated. It was therefore decided to use a TCS M1 decoder.
BB fixing screw
To remove the body it is first necessary to remove the front bogies to provide access to the screw fixing the body to the chassis.
BB capacitor

The speedometer cable between one of the driving wheels and the body should ideally be removed by undoing the nut holding the cable in place on the wheel. It is just possible, with extreme care, to remove the chassis from the body without disconnecting the cable, as shown here. It is also sometimes possible to remove the metal securing plate from the body (though this can be as difficult to replace as the nut on the wheel!).

The first task is to disconnect the capacitor from the motor terminals and solder the grey wire from the decoder to the top terminal and the orange wire to the bottom motor terminal.

BB connecting decoder

Once the orange and grey wires from the decoder have been soldered to the motor contacts the other connections can be desoldered, one side at a time. This is so that the black wires from the trailing bogie do not get mixed up. It can also be important to do this a side at a time as some models use red wires for both pickups!

Desolder the red wire and connecting black wire (from the trailing bogie) from the capacitor, then resolder these two back together with the red wire from the decoder. Use heat shrink sleeving or insulation tape to isolate the soldered connection from possible metal contact.

Repeat the task for the black wire (or other, longer red wire in some cases!) and dispose of the capacitor.

BB with hard wired decoder
The white, yellow and blue wires can be trimmed back to the decoder as these are not required.

Using a Sellotape sticky pad, secure the decoder to the top of the chassis. Gently manoeuvre the chassis into to the body shell and replace the secure screw a the front of the loco.

The loco can now be tested using address 3 to ensure that it actually works. If everything seems all right, then the loco can be programmed to the desired number (for this particular loco 81 was used).

NMRA socket on recent MN

It is possible to store the decoder (if it is very small, like the TCS-M1) in the Merchant Navy by sliding the decoder into the tiny void between the weight at at the front end of the loco and the body casing.

The latest versions of the Merchant Navy class loco are DCC ready with an 8-socket NMRA board in place at the front of the chassis. However pin 1 is not numbered - indeed there are no helpful markings on the board at all!

There is no need to make any changes to the loco with the NMRA board installed - just insert a small DCC decoder with a NMRA plug attached, such as a TCS M1-P available here. The TCS DP2X-UK decoder, a no wires plug and play decoder, will also fit this loco type.


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