Decoder Fitting for OO Gauge Models Bachmann's Class 03 diesel shunting locomotive sits alongside a pile of plug and play decoders of various types and some of the basic tools required for plug and play decoder installation which includes jewellers screwdrivers and tweezers Part 1: DCC Interface Sockets By Nigel Burkin Introduction Four major components make up a basic digital control system for model railways: the controller (cab, throttle); power station (booster); command station and decoders. Many systems group the first three components together into one box or base station and the 'E-Z Command' Digital Control Centre (36-500) is a good example. Others systems, such as 'Dynamis', combine the command station and booster in one box with separate controllers which is the most common arrangement. Most modellers usually experience little in the way of problems rigging up the basic system. Where real anxiety can arise for newcomers to DCC is with decoder installation, the fourth key component of a digital system. While my previous articles have looked at decoder fitting to N gauge models; it is the turn of OO gauge models, starting with those equipped with a DCC interface and leading on to those older models without an interface at the present time. It is fair to say that there is a bewildering array of different mid-sized decoders around 1 to 1.5 amp rating from which to choose, most of which will suit OO gauge models. To N gauge modellers, it may seem strange to hear that there are challenging locomotives to convert in the relatively roomy world of OO gauge. This is true, particularly at the smaller end where space for decoders competes the ballast weight necessary to give the locomotive sufficient traction to pull a train of reasonable size. Many smaller tank engines and diesel locomotives such as the Class 03 and 04 shunters will have challenged the designers at Barwell when it came to providing a DCC interface socket. Of course, as modellers, we are demanding; expecting to see cab detail and other features which further puts the squeeze on space. Fortunately, most new OO gauge models are equipped with DCC interface sockets and pins. All of these socalled 'DCC-Ready' or 'DCC Enabled' models can be equipped with a decoder quickly - its just a matter of choosing the correct decoder, a process assisted in the Bachmann range with its DCC icons. Sometimes, the hardest part is removing the locomotive body shell! Mobile Decoders Decoders designed for locomotives and multiple units are described as 'mobile decoders' for obvious reasons and that distinguishes them from accessory or stationary decoders; the latter being used to power layout features such as signals and turnouts. Of the bewildering range of 1 decoders available today with their numerous features, we are starting with plug and play decoders and their use in DCCready locomotives. Decoders may seem like an added expense to newcomers. In fairness, that tiny circuit board has a great deal of functionality for the price, making the independent and flexible control of a model railway possible. They have a rectifier to convert the constant track current of around 16v AC to the more common 12v DC so it can be used by the motor and on board lighting circuits. Decoders are also controllers in that they interpret specific instructions from the command station and respond to them accordingly. The ability to control a model independently of all others on the layout is due to the unique address and control features of the decoder. Operating features can be adjusted to suit the operating conditions existing on the layout; to suit a particular type of locomotive and for certain lighting effects by making adjustments to the decoder settings called configuration variables or CVs. The menu of features together with the various settings are detailed on the decoder instruction leaflet. Some decoders are equipped advanced features which include two-way communication, transponding, the ability to use 'uninterruptable signal processing' (USP) devices and advanced lighting features. Of course, there is the growing popularity of digital sound too, and all of these features can be found on off-the-shelf decoders - at a price! The number of functions also varies;
diesel and electric era modellers usually need at least four functions to independently control the on board lighting features. Steam locomotive modellers may opt for decoders with one or two functions because the lighting requirements might not be so important. Buying Suitable Decoders When making purchases of decoders for DCC-ready models for the first time, check the type of interface that is installed in the model. Is it a 21-pin, 8-pin or, in the case of some small OO gauge models, a 6-pin interface socket? Furthermore, how many functions are required? Starting with the 21-pin decoder; this type of decoder is a direct plug-in type with no wiring harness. The circuit board interface consists of two rows of pins which fit a socket block built onto the edge of the decoder board making it simple to install. It should be fitted with the large block uppermost. The 21-pin decoder has become popular because of its ease of installation - no wires to contend with, not even with sound decoders! An older but still much used interface socket found in some models in the Bachmann range and many others is the 8-pin which is also easy to use with direct plug and play decoders where the pins are soldered to the decoder board or decoders fitted with an 8-wire harness wires and a plug. In the case of a 2 or 3-function decoder there are no additional wires. A 4-function decoder has nine wire harness wires, one of which is the purple one for the fourth function (or F2 on the controller), which is not connected to the plug. Those unaccustomed to fitting decoders may think the purple wire has come loose from somewhere, but that arrangement is quite normal. Small tank and shunting locomotives are increasingly being fitted with 6-pin interface sockets, normally associated with N gauge models. Small OO gauge models are Different types of plug and play decoders including (from left to right) the 21-pin 3-function decoder; 21-pin 4-function digital sound decoder; 8-pin direct plug-in decoder; 6-pin (micro) decoder and 8-pin HO/OO gauge decoder with wiring harness. unlikely to exceed the typical power limit of a smaller decoder, so the space saving is a benefit. When choosing a decoder, bear in mind that many of the specialised features in expensive decoders are unlikely to be needed for the majority of models. The very minimum requirement for good performance is fine motor control features, often called Back EMF (BEMF); silent drive capability which ensures there is minimal noise from the motor; lighting functions (one for steam locomotives and two to four for modern locomotives) and a minimum continuous rating of 1 amp in total. Bear in mind that the continuous rating will include the power supplied to the function output too, so of the full 1 Amp rating, between 200 and 400 milliamps may not be available to the motor depending on the type of decoder. Ensure you have at least 0.5 amps dedicated to the motor. The Basic Principles Instruction leaflets supplied with DCCready model locomotives provide specific details of how to fit a decoder, so its worth reading the them before starting work. Key information includes locating all of the securing screws and, in the case of certain specific models, where the decoder is actually located in the model. Once the body shell is removed, the dummy plug is usually simple to locate, being plugged into the interface socket. Let's assume the model is in good working order. The analogue plug is removed from the socket and placed in a safe place should the need to return the model to conventional DC control arise in the future. Next, examine the circuit board adjacent to the socket carefully and identify pin No.1 - it should be marked on both the instruction leaflet and on the circuit board. This ensures that the decoder is plugged in the correct way round so all board features such as lighting, function correctly. Don't panic should you plug a decoder in the wrong way round, it is unlikely to cause damage. The lights might not function correctly and the model will run in reverse to others in the collection. For 8-pin connections, the orange wire is connected to Pin No.1, while 21-pin decoders are aligned with the connection block uppermost. 6-pin decoders have a spot adjacent to pin No.1. Once the decoder is fitted, place the model on the 'programming' or 'service' track to test the installation by asking the digital system to read the address. It should read the factory default setting of 03 for all new decoders. During this process, the model may inch along the track as it receives the 2 'programming' commands. Once the address is confirmed, allocate a unique address to the model and, in the case of the Dynamis system, a name for the locomotive too. Once this has been confirmed, remove the model, tuck in any wires so they are not pinched between the body and chassis and refit the body. It good practice to add insulation tape to the surface to which the decoder will be placed. This could be adjacent to the socket for a direct plug-in type or where it is going to be attached in the case of a decoder with a wiring harness. Decoders can be secured with double-sided foam pads, double-sided tape and even a small strip of insulation tape. Do not wrap the decoder in tape because many require an air flow to assist with heat dispersion and for normal operation. 1. The Bachmann Class 47 is a completely up-to-date design with a circuit board allowing sophisticated lighting and equipped with a 21-pin DCC interface. It is an easy model to convert to DCC and an excellent one to demonstrate the basic principles. 2. Using the supplied instructions for reference, locate all of the retaining screws, including those under the cab area. There are six in total in the case of the Class 47. 3. A slip of styrene card inserted between the body and chassis where there are body clips will help to ease the body from the chassis without breaking anything.
4. Inside the Class 47: a large diecast weight encloses a 5-pole motor with twin flywheels. On the top is located the circuit board and the 21-pin DCC interface. This arrangement is fairly typical of most diesel models. 5. A close up of the 21-pin DCC interface and analogue plug. Note its orientation in relation to the components on the circuit board, with the black oblong connector facing uppermost. 8. The 21-pin installation is as simple as it can possibly be for a conventional diesel locomotive conversion. The decoder simply pushed down onto the pins and the model tested before the body is replaced. Adapters Many modellers choose to use decoders with specific features for a particular purpose which may only be supplied be with an 8-pin plug. This will not suit Bachmann 21-pin equipped models, so an adapter is required. Item No. 36-559 in the Bachmann range is an 8-pin to 21-pin adapter perfect for the job. There are adapters available for the reverse too, so not all is lost! locomotive is on the move or not. Digital sound is made possible through this constant supply of current too. Digital sound decoders have all the features of mobile decoders with several added features: an amplifier; volume control, speaker output and additional memory to store sound files as small packets, to be replayed at the appropriate time. Bachmann's catalogue includes digital sound locomotives which are equipped with a sound decoder and a speaker too. The chassis of the locomotive is adapted to hold the speaker and the circuit board wired to accommodate the speaker connections. Usually, the decoders fit a 21-pin interface with the speaker connection through the circuit board. You can buy and fit 21-pin sound decoders with specific sound files for a given locomotive. It is worth examining the circuit board of up to date issues of models to see if there are speaker connections on the circuit board, probably marked as 'SPK-' and 'SPK+' or 'SP-' and 'SP+' depending on the model. The sound decoder may be plugged directly into the model like any 21-pin decoder and the speaker leads soldered to the connections on the circuit board. 9. Fitting an 8-pin plug to a model equipped with a 21-pin interface requires a special adapter such as the Bachmann 36-559. 6. It takes a few seconds to disconnect the plug. Store it away safely in case it is needed again. 11. In 2011, Bachmann issued its popular Class 57 with a digital sound decoder loaded with realistic sounds recorded from the full size locomotives. 10. An 8-pin decoder plugs neatly into the adapter, opening up the choice of decoder that can be used with a 21-pin interface. 7. Align the decoder so the oblong block is uppermost and the pins match the holes in the decoder. There are only 21 pins, so there is one apparently missing from the two rows making up the interface which matches the blanked hole of the decoder. Digital Sound One of the features of digital systems is the continuous supply of current to the track - the track is always live enabling constant lighting and efficient communication between the command station and decoders no matter if the 3 12. Internally, the model is equipped with a 20mm by 40mm speaker fitted beneath the fan grilles (nearest the camera) and a 21-pin digital sound decoder fitted to the digital interface.
13. It is possible to fit a digital sound decoder to many of Bachmann's 21-pin DCC interface equipped models because the circuit board has provision for the speaker output via the interface and terminals along the edge of the circuit board. In the case of the Class 47 and 57 model, the terminals are indicated with the legends: 'SP-' and 'SP+'. 14. I utilised the speaker connection terminals of the circuit board in the Class 411, 4-Cep model to install a 21-pin sound decoder and bass enhanced speaker to the model. The terminals are indicated with a red arrow. 15. The identification letters were to be found on the underside of the circuit board of the 4-Cep model: 'SPK-' and 'SPK+' as indicated by (A). The auxiliary (B) terminal should be ignored. Trouble Shooting Rarely does a plug and play installation cause a problem in my experience and conversion can be as quick as 60 seconds if the decoder interface is as accessible as the one installed in the MPV! Sometimes, the locomotive body refuses to go back as it should due to displaced cab mouldings or wires that have escaped from their stays. Real problems arise from inadequate masking of exposed metal components which short on decoders and the contact usually destroys the decoder, or at least disables it. Experienced DCC users are no strangers to this experience and when smoke escapes from the decoder there's no getting it back in no matter how hard one tries! Sometimes a converted model refuses to work for no apparent reason. Check the locomotive wiring to see nothing has come adrift and solder points on the underside of the circuit board are not coming into contact with metal. One experience I had with an 8-pin socket was to find the underside solder points were touching the diecast chassis, a problem easily solved with insulating tape, so it is worth taking a look under the circuit board. One useful feature of virtually every decoder is the factory reset mode. A decoder can be instantly returned to its original settings including address 03 and I have revitalised many a decoder with this setting including decoders that were positively dead. The instructions supplied with the decoder should give details of the correct Configuration Variable and the value to enter into it. Clearly, a model should be in full working order and be tested before a decoder is installed. Should it fail to run after installation, even though it was fine before the conversion, it indicates a problem with the model's electrics or the decoder itself. In the case of the former, return the model to the retailer for repairs or replacement. In the case of a faulty decoder, look up the warranty cover and see if it cannot be repaired or replaced. It's worth trying the decoder in another model to be sure! DCC-ready decoder installation should be a routine job which takes only ten minutes per model to complete - less for a model such as the new Class 350 'Desiro' EMU where the decoder interface socket is conveniently hidden in an underframe box, or the MPV where the socket is hidden under the large RHTT water tank. Basic tools and a tidy workbench area are all that is necessary for a clean and tidy decoder installation, so do not be put off by the apparent complexity of this task - it is literally plug and play! 16. Many of the Bachmann steam locomotive range are equipped with 8-pin decoder interface sockets. The Standard Class 5MT is one such model, the British Railway Modelling limited edition No. 73050 is the model shown. 4 17. The socket is located in the locomotive itself (some steam locomotive models have sockets in the tender). The body is removed by releasing the screws at the extreme ends of the model and detaching the speedometer drive link. 18. Tweezers are used to tease the analogue plug from the socket. Pin No.1 in marked on the circuit board, as indicated by the arrow. 19. Plugging in the decoder is easy, with the plug being aligned so the pin connected to the orange harness wire goes in socket hole No. 1. 20. A convenient plastic box is fitted to the model which will accommodate and protect a typical HO/OO gauge decoder. Failing that, the decoder can be attached to a suitable surface with double-sided adhesive tape.
21. The Modelzone special edition Class 03 is a very attractive model. It is equipped with a 6-pin interface (normally associated with N gauge models) making best use of the limited space space in the model. 24. Perhaps one of the easiest multiple units to convert to DCC is the Class 350 'Desiro' EMU which was released late in 2011. Only one decoder is needed per train (in common with many other multiple units in the range) because its couplings have electrical connections to provide power for all lighting circuits. 27. By far the simplest conversion has to be the Multi Purpose Vehicle (MPV) freight EMU which has the circuit board and a 21-pin interface hidden under the RHTT water tank. 22. Bachmann offers a 2-function decoder which is a direct plug-in to a 6-pin DCC interface socket. The No.1 pin is marked on the analogue plug. 23. The new decoder is shown fitted, with the model which will be concealed under the cab. No wiring is involved and the decoder will be completely hidden. 25. One of the underframe boxes of the powered vehicle is removed by releasing one screw to reveal a space with a 21-pin interface and its analogue plug. 26. It takes about 2 minutes to convert this model if a tiny piece of 'Blu-tak' is used to hold the screw in the screwdriver to make refitting the equipment box easier to do. Otherwise, the screw is easily lost! 28. It takes a few seconds to remove the tank from the powered vehicle and a few more to remove the analogue plug and fit the decoder. Making decoder access simple for conversion is an increasingly common feature of the Bachmann range. N Scale Nigel dealt with N scale decoder fitting in Volume 11 No. 3 and Volume 11 No. 4 Nigel also dealt with a general introduction to DCC in Volume 10 No. 4 Copies can still be obtained from the Club office on: 01455 841756 All photography by Nigel Burkin 5