Installing DCC decoders in a Bachmann Class 108 Diesel Multiple Unit

Click on each image for a more detailed view.

Last updated 29 March, 2020
Bachmann 108

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

This installation involved installing two decoders, one into the power car (left) and one into the trailing car. The power car had a Zimo MX63R decoder (shown left but now superceded by the MX630R) installed and the trailing car had a TCS FL2 function only decoder fitted to control the lighting.

Underside of Bachmann Class 108
On the Bachmann Class 108 the body is secured to the chassis with one screw at the front of each car, but is hidden by the bogie. It is necessary to remove the bogie by removing the screw in the centre of the bogie (for some reason this was a nightmare to get back into place!).
Bachmann Class 108 body fixing

Once the bogie has been removed the screw holding the body in place can be clearly seen. It is very small, so a small philips style screwdriver is required.

Once the screw has been removed the body can be separated from chassis. This is not a very easy operation and great care needs to be taken when holding the model not to damage any of the undergear parts, some of which are very fragile. The best way is to try to gently wiggle the front end away first. You will also notice that there are some lugs holding the body in place along the sides - running a finger nail between the body and chassis is the quickest way of releasing the body.

Gently separate the two parts, being careful not to bend the long copper contacts inside (which operate the internal lighting).



Bachmann Class 108 with dummy plug

Installing a decoder in the 108 is really very straightforward. Once the body has been removed the location of the socket for the new DCC chip can easily be identified at the rear of the loco. Gently remove the small PCB in the NMRA socket by levering it out, being careful not to bend the copper strips for the internal lighting.

Bachmann Class 108 decoder socket

Once the existing PCB has been removed it is obvious which way round the new NMRA board should plug into the socket as pin 8 is labelled clearly on the underlying PCB. The plug on the decoder should be aligned so that the orange wire (pin 1) goes into the socket OPPOSITE pin 8.


Bachmann Class 108 decoder installed

Bachmann have cleverly designed a location for the decoder on top of the motor housing. Secure the decoder with a self adhesive sticky pad (Sellotape Sticky Fixers from any good stationers are ideal) and neatly position the wires so that they do not cause an obstruction when replacing the body.

The decoder can now be programmed.

When replacing the body, be careful not to bend the copper strips or this will render the internal lighting inoperable. Also make sure the body is fully snapped back into place front and rear.



The decoder in the dummy car was installed in a similar way to the method outlined above..

HOWEVER - the decoder used was a TCS FL2 with one of the NEW SHORT harnesses with plug specifically made by TCS for the FL2, and available as a spare. Any longer harness and the wires are difficult to hide. The decoder sits against the toilet wall with the wires going over the top of the wall. The decoder has to be programmed so that the lights work in the OPPOSITE DIRECTION to those in the power car. It was also necessary to reprogram CVs in the decoder as follows to get the decoder to switch the lights automatically when changing direction (note these instructions apply ONLY to TCS decoders):











With lighting only decoders you might find it necessary to provide a load in order to program the decoder. This can be done by placing both units on the programming track and programming the trailer car first. Then remove the trailer car, after checking that the lighting works correctly in it, and program the power car.

One further issue experienced was internal lighting operating in only one direction. This was caused by the copper contact strips not aligning properly with the lighting board contacts in the roof of the carriage.


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