Installing a DCC chip in a Bachmann 4MT Steam Loco
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Last updated 29 March, 2020
Bachmann 4MT

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

You will need two small watchmakers screwdrivers with flat heads to undertake this installation. You will also need a lot of patience and fine control in order to prevent damage to a lot of finely detailed body parts. You have been warned!!!!

I was disappointed initially to find that no instruction sheet was included with the model, though it can be downloaded from the Bachmann site. However, once I had seen it I realised that it was of no use whatsoever in assisting with a decoder installation. Any instruction sheet which just states "Remove the two screws indicated on the diagram" has clearly been written by somebody who has either never seen the loco or clearly not attempted to take the loco apart, especially when you examine the loco to find that one screw is extremely difficult to access and the other almost impossible! The diagram illustrating the position of the screws fails to show or mention the finely detailed mouldings hiding the rear screw.

In addition the instruction sheet advises users to "Remove the block from the centre of the boiler to provide space for the decoder". If the weight is not needed why put it there in the first place?? I would NEVER advise removing weight inside a loco unless absolutely necessary. Clearly weight is there for a reason and if you remove it then the weight of a decoder will in no way compensate for the loss of this block and traction will be severely affected.

I had intended putting a 6-function decoder into the loco with the intention of adding individually controlled loco lamps later on but as you will see I gave up on that idea as this is a loco I never want to take apart again.

Bachmann 4MT

Bachmann 4MT


The body is, indeed, secured to the chassis with just 2 screws, one at the front and one at the back. However, although the front screw is obscured by the pony it can just be accessed with a little pressure being exerted to move the pony to one side, though not all of the screw is revealed even then. You will need a finely tipped screwdriver to undo the screw.

Accessing the rear screw, though, is the most difficult job. Why manufacturers produce models which they know are going to be accessed by modellers to install DCC decoders have to design the model with almost no thought given to making access simple is beyond me.

I have no idea what the parts obscuring the rear screw are called but hopefully the description and accompanying photographs will help identify them correctly. Whilst it was eventually possible to get to the screw extreme care is needed at this point to avoid damage. Located over, and completely obscuring the screw, is a small plastic part (A) sitting between what appear to be two jaws. At the top of this plastic part is the fine bar (B) which comes from the front of the loco. This bar can be detached from part (A) by prising it gently away from (A), to reveal a small lug on the end of the bar. The bar needs to be moved gently to one side. (A) now needs to be removed from between the jaws, there being lugs each side of (A) securing it in place. I used the smallest watchmakes screwdriver I had to achieve this, but it took a lot of time to gently lever it out, levering a little each side alternately. Once (A) is removed the screw becomes accessible. The rear screw also holds in place the bar connecting the tender. When the rear screw has been removed, slide this bar out from between the chassis and the body.

Once both screws have been removed the front part of the body will move apart from the chassis quite easily with a little help. The back, though, is far more difficult to release as there are a number of fine body parts attached to the body which appear to overlap the chassis (in fact they don't but just fit very closely). With a small flat headed screwdriver gently lever the back part of the chassis from the body. The chassis fits very tightly to the body, but be careful not to use too much force. You will need to gently lever at the back when the front has been levered up a few millimetres. Keep alternating between the two ends until the chassis seems to be free of the body.

There is a part of the body moulding (shown on the photograph, left) which seems to have been fixed to the chassis, perhaps by glue. There is a danger that this might snap off as you try to release the body - fortunately on this particular loco it just sprung away from the chassis when a little presure was exerted but you might find it necessary to get a modelling knife or something similar to try to get between the end of the moulding and the chassis.


Bachmann 4MT

Once you have managed to get inside you will see that the loco is DCC ready, having a socket installed at the front of the loco. Gently lever the dummy plug out of the socket.

Markings to indicate pin 1 are not clear and I only noticed the number on the board when I examined the photograph (left). Just make sure the orange wire is at the front of the loco.

There is little space inside the loco, so I abandoned the idea of adding lighting and also of using the 6-function decoder which had a lot of wiring attached to the plug. I tried a TCS DP2X-UK decoder but this would not fit back inside the boiler space, being too wide to fit the aperture. A small decoder is required so eventually I used a TCS Z2-UK decoder, one of the smallest decoders on the market, with a shorter harness for UK locos.

It is also possible to disable the capacitor by cutting through one of the legs securing the capacitor to the circuit board with a pair of wire cutters. This action is sometimes recommended to improve the performance of the loco with a decoder installed, but with many modern decoders it is not necessary and also be aware that disabling the capacitor may invalidate your warranty. Leave the two chokes (one each side of the socket) in place.

Bachmann 4MT

Firmly push the plug attached to the decoder into the socket, being careful not to bend the pins. Make sure the decoder is correctly orientated, with the orange wire at the front left.

It is suggested that you do any programming of the decoder, before replacing the body, to test everything is working correctly.



Bachmann 4MT

The decoder wires will need to be folded so that the decoder can be pushed into the void in the front part of the boiler between the weight and the outer casing. If you have used a decoder without any sheathing you will need to provide some protection around it to prevent short circuits. Fortunately this TCS decoder comes fully protected.

Replace the body carefully making sure that you don't break any of the finely detailed parts. Remember to insert the tender coupling bar before finally snapping the body back into position. The one plus to this installation was that everything went back together much more easily than it came apart!!


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