Decoder Installation


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When selecting a DCC locomotive decoder the following should be taken into consideration:

Locomotive stall current - this is the maximum current drawn by the locomotive when the motor is stopped at the normal running speed. This is tested with a multi-meter in series when a locomotive is running under normal DC control.
Functions - Functions are additions to the normal running of the locomotive, for example directional lighting (normally F0).
Examine the locomotive internally for the space available to locate a decoder - consider the decoder size and the wiring. Once the current rating and functions have been determined look at the space available to locate the decoder, or see if the locomotive is DCC ready. DCC ready is a term used to describe locomotives fitted with a socket to allow the decoder to be easily fitted by simply removing the factory installed plug (this makes the locomotive work under DC use) and inserting a decoder with a corresponding plug attached. Locomotives without the DCC socket need to be hard wired - the decoder has to be installed by soldering the decoder wires to the correct place on the locomotive.

Always ensure a locomotive is in good condition before fitting a DCC decoder. Check the wheels for dirt, check the brushes and springs for excessive wear and accumulation of carbon and motor dirt - replace if necessary. Also check the mechanism for hair/fluff, carbon debris, general dirt and over use of oil particularly the gears and the commutator. Always check the magnet for stray metal e.g. track pins that may cause a problem to the decoder. Also check any wiring for breaks or traps or any exposed cable strands. Do not over oil! A DCC decoder is not a magician - it will not make a dirty or poorly maintained mechanism run better. 

If possible test your new decoder on an ESU 51900 Decoder Tester (image below) to ensure the decoder works correctly prior to installation. This excellent addition to any DCC enthusiasts 'gadget draw' allows NMRA 6, 8 and 21 pin DCC plug fitted decoders to be tested together with decoders designed for hard wiring with no plug fitted. Sound decoders can also be tested.

Installation - Non DCC ready

Once the decoder has been selected it is important to clarify how the power from the track gets to the motor under normal DC use. The decoder can only be located in the locomotive once the motor is completely isolated from the pick ups. Damage may be done to the decoder if a circuit is still present from the track to the motor with the decoder in place. Always insulate solder joins with heat shrink tape to prevent any contact with the decoder wires and the chassis/wheels. Wiring is simple, the black and the red wires are the pick ups from the track; the orange and grey wires are the connection to the motor. The remaining wires are function wires with the blue common. See decoder manufacturers decoder instructions for more information.


The image above left shows a hard wired locomotive with the decoder wires attached as follows - on this side of the chassis the two motor brush spring covers can be seen - silver colour. These are solder contact points for the motor wires and the orange and grey wire can be seen attached. The red wire connects to the chassis pick ups via an existing wire with the solder join covered in black heat shrink tube. The black wire is attached to the chassis as the locomotive has a live chassis that has been insulated from the motor. The image right shows a Hornby tender drive mechanism hard wired with the decoder and wires fixed down ready for the tender body to be fitted.

What about Bachmann Split Chassis locomotives?

Split chassis locomotives are a little bit more 'fun' to install a decoder. The main problem is that to get at the motor the chassis needs to be completely disassembled in most cases. This may be very daunting for some DCC users as you will end up with a kit of chassis parts! Be very careful when removing cylinders and motion brackets as these are usually glued to the chassis and are very easy to damage. Also mark the orientation of the motor using the manufacturers label to ensure the loco runs the correct way when reassembled. Before taking the chassis apart, check for space to locate the decoder. Often the chassis block will need cutting to fit the decoder. It is vital that when you solder the decoder wires to the motor tabs you completely cover the joint with heat shrink tube to prevent the tabs touching the chassis when reassembled. For extra protection cut a small piece of insulation tape and cover the chassis surface on both sides where the power springs usually locate. The images below show a Bachmann J39 0-6-0 being fitted with a TCS M1 decoder. This decoder has a 1amp rating 2 amp stall.

Chassis sides before cutting to locate the TCS decoder. Chassis sides showing the area removed to locate the TCS M1 decoder.
Not particularly clear but this image shows the finished installation with the TCS M1 decoder fixed with black sticky putty into the chassis cut out. Be careful when fitting the body as it is very easy to chop the decoder wires! The easy way! A DCC ready Hornby 8F 2-8-0 is fitted with a TCS DP2X-UK decoder. No wires just a simple plug fit! The following section gives a little more information on DCC ready locomotives.

Installation - DCC ready

Generally the hardest job when fitting a decoder into a DCC ready locomotive is removing the locomotive body. Once you are inside simply pull out the DC plug noting the location of pin1 and insert the decoder plug. Most locomotives have pin 1 notation but do not put the body back on until you have tested the locomotive runs the correct way. If not turn the decoder around and re-test.

A Bachmann 8 pin decoder installed in a Hornby locomotive. The decoder has been plugged into the DCC socket to the left of the decoder. The loco manufacturer has left sufficient space for the decoder and wires in the loco body or chassis. In certain cases a DCC socket is fitted but no provision to locate the decoder or cables. If space allows fit a TCS DP2X-UK decoder as this is constructed on a board the size of the older DCC 8 pin blanking plugs and has no wires as the pins are located on the underside of the decoder.


Can any DC analogue locomotive be fitted with a DCC decoder?

The simple answer is yes - even Thomas the Tank and Friends as shown below!

 Regardless of age, manufacturer or motor type a DCC decoder can be fitted with a DCC decoder. The question should be are all locomotives worth fitting with a DCC decoder? The simple answer has to be no for several reasons:

  1. Older locomotives often have larger mechanisms with high stall currents. The gears were not designed for slow running and the pickups only work on selected wheels. A high amperage decoder may be needed and the locomotive will not perform any better. Triang, Wrenn and Hornby Dublo locomotives are simply not worth fitting with a DCC decoder.
  2. The fitting of a DCC decoder may require severe alterations to some older mechanisms e.g. Wrenn and Hornby Dublo. This will devalue the item as a collectors item.
  3. If you are having a decoder professionally installed, the time taken to install the decoder and the cost of the decoder may not be worthwhile on some mechanisms. 

What if I don't feel I can fit my own locomotive decoder?

We offer a OO gauge locomotive decoder installation service for both DCC ready and hard wired locomotives. We will install your customer supplied decoders or fit decoders of our own choice. For standard DCC ready locomotives (fitted with a DCC socket) as standard where possible we will fit the generic decoder unless otherwise requested by the client i.e. Hornby decoder in a Hornby locomotive. In some models the manufacturers do not provide sufficient space for the decoder and or the cables. In these locomotives and in older non DCC locomotives  we usually fit TCS decoders.

Please note:
Aspects of the Hornby DCC range are not compatible or selectively compatible with TCS decoders. The Hornby Select and Elite may have issues with TCS decoders depending on when they were manufactured; and both the DCC power tack and standard power clip may cause problems. It appears that the Hornby apparatus distorts the signal received by the input stages of the decoder outside the pure NMRA specifications of the TCS decoder.  

If you require more information please contact below.





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