Page last updated on 06/08/2008

DCC -  Digital Command Control

Comparison of the two methods of train control..

Normal dc systems (These could be called ‘Analogue' control systems) to move a locomotive we proved nominally between 0 and 12volts dc to the rails. When full voltage is supplied then the loco will move at the fastest speed the motor can muster. If we want the loco to run at half speed then the supplied voltage is reduced accordingly. 

e.g.. Half rail volts equals half speed, three-quarter full volts equals three-quarter speed etc (this isn’t quite correct, but it’s near enough for this example).

DCC systems supply full volts (typically 16 to 18 volts ac) to the rails all the time and each loco has an ‘on board’ DCC decoder fitted (Micro chips on small circuit board). The decoder is in constant connection to the rails via the locos wheels. When a digital command signal is sent out by the operator’s DCC controller it’s received by all the decoders. Normally only one decoder will respond and supply the commanded voltage to the locos motor e.g. full volts for half the time will give half speed running or full volts for three-quarter of the time will give three-quarter speed etc.  For those who noticed this paragraphs opening comments re 16 to 18 volts ac being on the rails all the time. This is correct, but the 'ac' isn't a typical sine wave ac it is more of a hybrid square wave form. The decoder uses this track power ac and converts it in to dc to feed the motor and any function outputs etc. Overlaid onto this is the digital command signals to instruct the decoder what to do.

For those who are technically minded the system of motor voltage control is called Pulse Width Modulation and a simple example of four  typical states of modulation re shown below - 1/4 speed, 1/2 speed, 3/4 speed and full...

So every loco on the DCC controlled rails has a decoder fitted, so they all receive the data commands simultaneously, but only the decoder that has the unique digital address assigned to it will respond to the digital data signal being sent along the rails at that time.  All the other locos decoders will ignore the commands and continue doing whatever they were last instructed to do!  Once the correct decoder has seen the data arriving, it will act upon these commands and operate the device it’s connected to accordingly - motor, lights, sounds etc.  Once it has been set, the device will remain at that setting until another unique command is received. What can now happen is that the operator can call up the address number of another loco’s decoder and send a digital address to allow this loco to move off. The first loco continues to run at its last setting. Hence we can now operate many locos simultaneously on the same rails. although we actually only drive one at any one time, as the others are doing what they were last set at. e.g. we can set the main line train running and then call up a loco in a siding and carry out some shunting etc while the first loco continues to run uninterrupted.  Of course now we can have one loco stopped in say a platform and bring a second loco right up to the stopped one and even couple the two together without the first moving or the need of special isolating track sections. The two locos can both be set to run coupled together if wished, which is called a consist (An American name for what is know as double heading in the UK) and both locos motors are set to be controlled by one temporary address number.

There is normally an “All Stop” button provided on the controller or console for any emergency!  This will stop everything and once the problem has been resolved you will need, in most cases, to restart each loco again in turn.

DCC not only allows you to control many locos at once it also offers the opportunity to control signals, points, train lighting and on-board sound effects too. Add to this, in some systems, the option to have your PC running the railway and you can have a total train control system. Hence Digital Command Control! One advantage is that vertually all the DCC manufactures produce their products to be compatible and to a set of standards written by the NMRA  National Model Railroad Association which makes mixing and matching possible with differing makes of control systems and differing makes of decoder. Whether or not the decoders are factory fitted inside the locos or installed by the locos owner.

Some basic DCC systems will state “Simple two wire control” while this perhaps is true it isn’t often reality.   All electrical power needs to get from its source to the motor or decoder or wherever it is needed as easily as possible. Electricity is basically lazy and if an obstacle is placed in its path it won’t try very hard to get over the problem, it just lays back and rolls over!  This is often due to, and is called, a high resistance joint. So think of it as.... Power comes from the control unit onto the rails, from here it has to pass through numerous rail joiners (fishplates) to get from one track section to the next track section etc. Eventually it arrives at the wheels of the loco, then in most cases via wiper contacts touching on those wheels and then onto the decoder. Now, how many places of possible high resistance has the power passed through? Probably 20, 30 or 40 plus! I’ll list a few of them - Rail connecting clip to rails, two rail joiners per track section, point blades to stock rails, rails to loco wheels, wheel wiping contacts to the final connection to the decoder. Now each one of these ‘resistance places’ is a possible cause for trouble!

The main culprits are – Dirty rails, dirty wheels, dirty wheel wiping contacts and of course the loose and or dirty rail joiners/rail ends themselves.  Quite a few items! That’s without the possibility of the rail power clip being a poor connection!

How do you avoid all these? Well, by keeping the rails clean by using  a track rubber type cleaner and a loco’s wheels clean with the aid of a wheel cleaning set (Both available from model shops and manufactured by Peco for example). Cleaning of the rails only needs to be undertaken once every week or so and that’s where a layout is used regularly. However, if the layout is put away and not used for several weeks etc then the rails should be cleaned before use as they will have tarnished.

Don’t relying on ‘push in’ electrical connections (Track power connectors and rail joiners)  Solder the power wires directly to the outsides or underneath of the rails and seriously consider running a 'DCC power bus' or 'Bus main' (two wires) around the under side of the layout and tap off this as many times as possible to feed sections of track.  By keeping the locos wheels clean and don’t forget to clean all the rolling stocks wheels too as these equally deposit dirt onto the rails, improved running will result. While the above is aimed at the DCC user some of these good practice items should be observed by the dc user too.

So, to improve DCC operations it is recommended that the 'Bus main' pair of wires (we’ll call it a 'Bus' from here on) is run around the railway. Onto this bus are connected the running rails of all the tracks. The bus will improve operations many fold. Any problems such a high resistance rail joiners (fishplates) will be overcome, as will an improvement to the volt drop problem on larger layouts.  Some advanced DCC systems require data to be returned back to the control unit so these systems use an additional data bus, these can have as many as six individual conductors transferring data back and forth! But for the time being I’ll leave this detail and I'll only be concern with the bus (Power bus or bus main).

From the bus, there will be many connections between it and the running rails to ensure reliable power and data transfer into the rails and hence onto the loco’s wheels and the decoders. I advocate a DCC bus being made of at least 1.5mm² or better still 2.5mm²  solid wire as used in domestic wiring cables. Flexible wire for the bus can be used if preferred, and may be especially useful on portable layouts! If using a flexible wire for the bus choose a conductor size of at last 32/02mm while 50/02mm can be used on larger layouts. If you're using the solid conductor mains cable, strip out the two insulated conductors from the outer sheathing. Discard the outer sheath and use the two conductors - Red & Black or Brown & Blue. The bare (former earth) wire removed from the stripped cable can be saved and cut up for use as rail droppers perhaps? or as I have done, run this also around the layout and use it as a Common Return bus for everything else that’s not directly DCC controlled. e.g. Street lighting, building lights, colour light signal aspects etc.

There is debate as to whether or not the bus should be in a ring (each wire starts and ends back at the same place and is connected together to make a continuous ring circuit) I haven’t done this and haven’t encountered any problems and most DCC users normally opt for the Radial type of DCC bus (Radial being a wire or wires that start from the feed or input location and run out to the furthest point and terminate there). Once the bus has been installed, connect the DCC base unit’s output terminals to the bus. Then connect all the rails to the bus, ideally solder all connections to the bus to ensure reliable data and current flow. However, the use of 15amp type terminal strip blocks can be used at locations where soldering isn't considered easy or needed.  Simply, we now have a reliable bus (power & data highway) which our locos can pick up power and data commands from via the rails connected onto the bus wires  See the simplified layout for a DCC bus below…

The above drawing is very simplistic and is not meant as an actual design of track or railway. It is purely to show how a bus is connected from the DCC control unit via the two 'Bus' wires to the running rails.  Note: All the points shown in the above are Insulated frog type.

Having installed the DCC bus around the layout in suitable sized cable, there is now a need to connect the bus to the rails. This I recommend this being carried out using 16/02mm flexible wire in the same colours as the bus – red/black or brown/blue etc. called 'Droppers'.  I prefer to use solid copper wire droppers from the rails to below baseboard, then solder the flexible feed wires onto these droppers, cutting the extra length of solid dropper wire off once all  has been securely soldered.  However you can solder the 16/02mm flexible wire from the bus directly onto the rails if wished. The final connection is at the beginning of the bus wires to the base units terminals, here use 32/02mm wire.  All connections onto the bus should ideally be soldered. Simply remove a small portion of the bus cable insulation (about 20mm is ample) with a craft knife and and strip approx 10mm from the end of the 16/02mm feed wire, then wrap the track feed wire around the bared copper bus wire. Apply a pre tinned hot soldering iron to the two wires, wait a few seconds for the joint to heat and apply a little cored solder onto the joint (Not the iron) until solder is seen to flow into the wires. Remove iron and leave joint for some 10 or more seconds to cool, then cut off any surplus wire end. If you wish, a small amount of insulating tape can be wrapped around the joint to prevent it touching any other part of the bus. 

The two drawings below show solid wire droppers connecting onto the flexible wire that then connects to the DCC  bus.

Above are solid copper wire droppers before soldering and in the second picture after soldering to the outer web of the rail.

In the above pictures, P1 shows two Lenz decoders. On the left is the 8 pin connector plug and leads. On the right this decoder has flying leads for soldering directly into loco's where no manufactures 8 pin socket has been provided.   P2 shows the DCC bus running around the layout. Photos 3 & 4 show the main bus with track feed flexible 16/02mm wires soldered on and they they go off to the running rails (via the solid droppers from the rails in my case).

Programming Track... Most systems require a length of ‘Programme track’ to be available for setting up the on board decoders in each loco. This special track is often powered from a dedicated programming output on the base unit or console. It allows each loco’s decoder to be programmed without causing any changes to the all the other existing decoders already in locos on the main tracks. Where the console unit has a special Programming output it provides a lower current supply to the rails during programming mode to prevent decoder burn out should it not be installed correctly or the loco is defective etc.  However, it should be noted that not all consoles provide a separate programming output. The easiest means of providing a programming section of track regardless of the consoles outputs is to use the end of a siding. Shown below are two methods of how to wire this end of siding track section, depending on whether or not the console has the programming output. In all cases a pair of insulated rail joiners are fitted in the two rails at least the longest loco or multiple units length from the buffer stops and add about a further 50mm to ensure the items fit inside the insulated area easily. It’s then, depending upon the switches position, can become a totally insulated section from the rest of the railway and the siding line feeding into it too.

The diagram below shows the set up for a console without a Programming output and how the track at the end of the siding is wired to a DPST switch. When Programming is selected the rest of the railway is disconnected and only the end of the siding is DCC powered. 

The second diagram below shows the console with a separate Programming outlet and how the end of the siding track is wired to a DPDT centre off switch. Technically there is no need for the centre off position of the switch, but it's shown as a 'best practice' method to allow total end of siding isolation if required.

Insulated frog points will require a small modification to enable full DCC operation. The simple insertion of two link wires, or if a DCC Bus is used two new feeds from the Bus to the Vee rails, are all that's needed to ensure no matter which way the point is set DCC power is sent to all tracks. Thereby keeping all the track live without the point being set for that direction.

The drawing below shows the simplest method of just adding two linking wires...

Extract taken from the 'Electrical' Page.......

Short circuits caused by the metal wheels touching both rails at the rails closest place both pre and post insulated frog is more common on DCC fed layouts as both rails are permanently powered with opposing polarities. This can cause the main control unit to detect the short and trip out. The problem of shorting is easily overcome by fitting two insulated rail joiners after the frog on any problematic point on the DCC layout and then running in two linking wires from the two rails after the joiners and connecting them to there respective outer rails as shown in the diagrams above and below. 

Decoder installation into the loco’s will depend on several factors:-

a)      Age of the loco.  b) If the loco has Split Frame (Chassis) construction.  c) Space available for the circuit board.  d) Whether the loco is “DCC ready”  i.e. the loco has a decoder 8 or 21 pin NMRA DCC socket fitted by the manufactures.

Warning...Only ever convert a loco that's proven to run well on conventional DC before attempting to convert it to DCC. Converting a poor runner will result in equally or worst poor running on a DCC system.

STALL CURRENT TEST  In addition you should know the stall current of the loco’s motor as this will determine the choice of decoder to be installed. To find out the stall current you will require a normal dc train controller, a length of track (Not connected to any railway) and a suitable dc reading amp meter (digital or analogue multimeter with a dc ampere range of  at least 1.5amps (for “00” locos) DO NOT USE THE DCC ENABLED TRACK FOR THIS TESTING.

Connect one wire from the conventional controller to one of the tracks rails. Connect the other controller’s terminal to one side of a dc reading amp meter. Connect the opposite terminal of the amp meter to the remaining track rail.  You now have a meter connected in series circuit!  Place loco on the test track and while holding the loco in place turn up the controller to full power. The meter should now be reading the normal current flow.  Now stop the locos wheels from turning, or in other words stall the motor. Note the current being drawn on the meter  WARNING - DO NOT ALLOW THIS STALL CONDITION TO LAST FOR MORE THAN 5 SECONDS or the motor will burn out!      Once you have obtained the stall current select a decoder that will handle that noted stall current.  Most decoders will be rated between 1.0 and 2.0 amps dc continuous. For “00” and for “N” gauge the use of a 0.5 to 1.0 amp rated decoder is normally ideal.

“OO” gauge DCC Decoder Installation.

Unfortunately I can not make any comment on how to gain access to the insides of any particular loco, as the means of access varies considerably loco to loco. Please refer to the manufactures instruction leaflet or if not available then try their web site for maintenance access instructions.

How to wire a decoder. Firstly, if the loco isn’t DCC ready it must be determined whether or not the motor and its brushes are in contact with any metal of the chassis and hence to one side of the rail via the wheels of the loco. If it is, and most non DCC ready are, it can be  determined by using a multimeter switched to ohms and looking for a reading between either side of the frame/chassis and both brush connections (or motor feed terminals if the brushes aren’t accessible), if a reading is obtained then the motor brushes or motor terminals must be insulated from the chassis.  I can’t describe how to undertake this in detail, as every loco is of course different, but this action is essential to undertake. I have described below the basic conversion techniques I have found necessary on many 'generic' loco's and also I am showing how to convert some of my existing locos too.

Where the motor is insulated, then the existing wires from the wheels to the motor terminals have to be unsoldered at the motor end – Make a note of which colour wire goes to which side of the loco.  Once these two wires are removed connect them to the red and black decoder wires by twisting and soldering the ends together. Note the red wire connects to the right-hand side looking forward and black to the left-hand side.  Before soldering cut a small length of heat shrink tubing to cover the final joint and slide this onto one end of the wires, then twist and solder. Slip the heat shrink tubing over the cooled soldered joint and gently warm the tubing until it’s shrunk down and has made a nice insulated cover over the joint. (Use the soldering irons tip if you don’t have a micro warm air tool). Now connect the Orange wire to the motor terminal where the right-hand original wire was. Then do the same with the Grey wire connecting to where the left hand side wire came off

Other wires from the decoder are used to control lighting functions such as head lamps, rear lights etc.  Consult the decoder’s manual for full information on these functions.

Several style of non insulated motors are to be found – 3 or 5 pole open frame, Ringfield and Can styles.  Of all these,  the Ringfield is probably the easiest to convert and is often found in older Hornby and Lima tender drive steam locos and many Hornby and Lima diesel outline locos and DMUs.

When converting an older loco I would recommend that only the best quality of decoder is used. i.e Lenz Standard or Silver.  This will ensure that older style motors perform to their very best.

3 or 5 pole open framed motor is a little time consuming, but isn’t beyond the scope of this article and most people.

Having removed the loco’s body, view the chassis from above and on most older Hornby/Tri-ang loco's a ‘V’ shaped spring can be seen along the top of the motor, this retains both motor brushes under tension. One side has a slide on insulated sleeve. Locate and remove the push fit connector that’s located between the insulated sleeve and the actual motor brush curved upper part. This is normally a simple pull off fit and has a black wire soldered onto it which runs down to one side of the wheel set.  Cut off the black wire where it’s soldered onto the connector.  Discard the connector.  The black wire will be used later.

Strip around 12-15mm of wire insulation (16/02 is ideal) and use the insulation to insulate the opposite side of the ‘V’ spring where it touches the brushes top or use a similar length of heat shrink tubing.  This means now that both sides of the ‘V’ are insulated from the brushes.  Next solder the Orange wire from the decoder onto one motor brushes top section and the Grey wire to the opposite brushes top.  Be careful not to damage the insulation – slip a small piece of Paxolin or other heat resisting material between the brushes top and the insulated ‘V’ to prevent the insulation melting while the soldering iron is heating the brush/wire joint. When both are soldered visually check that the brushes carbon blocks are touching the motors commutator and there is no pull on the brushes from the attached wires.

Now slip a short length of heat shrinkable tubing over the black wire (removed earlier from the insulated side of the brush) and then solder the decoders Black wire to this. When cool, slip the tubing over the joint and apply a little heat to shrink the tube to form a good insulated joint. Finally connect the Red wire to the central screw that holds the ‘V’ wire in place by undoing the screw a little, stripping approx. 10mm of insulation from the red wire and twisting up the strands to make a solid wire then wrap this stripped end clockwise around the loosened screw. Tighten the screw to grip both the wire and the ‘V’ spring.

Place the loco onto the Programming track and check that the decoder can be read , normally its factory preset set to 3.  If all is ok then programme as needed.  

Once programming is completed test the loco on normal DCC operation. In the event of the loco running in the opposite direction to the controllers setting (e.g. reverse when forward selected) unsolder the two wires on the brushes (Orange and Grey) and reverse them.

When reassembling the loco body ensure the area chosen for the decoder’s final position is well insulated. Remember that the chassis is live and will cause a short circuit and destroy the decoder it if it’s not suitably insulated. This can be carried out by applying insulating tape to the area of the decoder’s location and then holding the decoder in place with double sided adhesive pads. Make sure decoders wires are taped clear of any moving parts too.

The Ringfield Motor is quite easy to convert.  Remove the body and note the style of motor and all its electrical connections.

Firstly, remove all the wires attached to the two motor's silver looking contact strips or their soldered connection ,  There may be two or more wires per connection, then cut off any crimped 'push on' connectors from the wire ends.  Its these silver coloured strips that hold the motor brushes in place too.  Solder the Grey and Orange decoder wires onto the silver strips (often the factory soldered capacitor gives a nice soldering point to resolder these wires onto). Now cut two 10-12mm lengths of Heat shrink tubing and slip one onto each of the two set of wires removed from the silver strips earlier.  Strip a small amount of insulation off these wires if not already stripped, and then solder the Red decoder wire to one and the Black decoder wire to the other. Slip the heat shrink tubing over the soldered joints ensuring all the stripped and soldered area is covered, then apply a little heat to shrink the tubing down to make a nice solid and insulated joint.   Place the motor assembly (Tender chassis) and the loco as well, which must be coupled to the tender unit to provided at least the one electrical path via the locos wheels, onto the set up track and select 'Programme'.  You should now be able to read back the manufactures setting.  Normally its factory preset set to 3.  If all is ok then programme to a new number as needed.   Once programming is completed test the chassis & loco body on normal DCC operation. In the event of the loco running in the opposite direction to the controllers setting (e.g. reverse when forward selected) unsolder the two wires on the Silver strips (Orange and Grey) and reverse them. 

When reassembling the loco body ensure the area chosen for the decoder’s final position is well insulated. Remember that the chassis is live and will cause a short circuit to the decoders printed circuit board and destroy it if it’s not suitably insulated. This can be carried out by applying insulating tape to the area of the decoders location and then holding the decoder in place with double sided adhesive pads. Make sure all the decoder’s wires are taped clear of any moving parts.

In the above:- Photo 9 shows a Hornby A4 tender drive Ringfield motor as supplied for normal DC working.  Photo 10 shows the capacitor and feed wires removed as this motor didn't run very well with the capacitor fitted. Photo 11 shows the completed DCC installation ready for the decoder to be fitted onto its plug. (The unused lighting wires are cut off short or tucked away neatly when the tender top is refitted). Photo 12 shows the newer Ringfield motor with a Bachmann decoder being used. Note: Here the capacitor is remaining and the decoders motor wires are soldered onto the capacitors leads where formerly the three wires per pick up where soldered. These wire have then been soldered together as a group and one of the decoders input wires (Red & Black) have been solder to that group then covered over by heat shrink tubing.

Ringfield-2  Conversion of the second type of Ringfield motor to DCC is possible, but does require more work. The important thing is to isolate the left-hand motor brush retaining clips screw which makes contact as supplied with the chassis and the brush strip.  The left-hand screw should be removed and then either replace it with a suitable nylon screw if one is available (a very hard to find item!). If not, then there are two alternative methods. 1) Remove left-hand screw and fit a short length of suitable sized heat shrink tubing over the screws head and a short way down its body. Shrink down the tubing and carefully refit the screw ensuring none of the tubing is damaged as the screw is driven home - Recheck with the continuity tester to ensure there is now no connection between the left strip and the metal chassis.  

2) The brushes contact left-hand contact strip will need a piece of insulation (Plastikard etc) fitted behind it and a Plastikard washer made up for the front side to fit under the screw head. Also I would recommend that a short length of insulation (Suitably stripped flexible wire insulation or heat shrink tubing for example) is fitted over the upper portion of the screw, up tight against the screws head and just long enough to pass through both sides of the silver metal brush contact strip. This sleeving together with the Plastikard washer will then prevent the screw from touching any part of the brush strip. Check after assembly there is no connection between the strip and the chassis with the multimeter on its OHMS range or use a battery powered buzzer continuity tester.

Unsolder or pull off the right-hand brush strips wire (often black) This wire will be reused later.

Having undertaken all that work, retest again that the left-hand and the right-hand brush strips are actually now fully insulated from the chassis with the aid of a multimeter set onto the OHMS range or the use of a battery powered continuity buzzer. Place one lead onto the chassis and the other onto the left-hand strip. No reading (or a buzz, if a buzzer is used) should be observed. Then leave the chassis test wire in place and move the other test wire to the right-hand brush strip. Again no reading or buzz should be present.

If all ok, then there is now the need to provide a connection onto the chassis for one of the decoders track pickup wires (The red wire). This will mean finding a suitable place for the red wire to connect onto. This, if you're lucky, can be a factory fitted wiring tab on the chassis. If no suitable tab exists then I found I had to use a small self tapping screw which was fitted at a suitable location. Do this by drilling a small hole into the chassis and then driving in the small self tapping screw, before fully tightening down the screw, loop the red wires stripped end under the screw head in the direction of tightening and then drive the screw down fully.  Solder the Black decoders wire to the existing wire that was removed from the right-hand brush strip. Cover this soldered joint with insulation tape or use heat shrink tubing.  Solder the Orange and Grey wires to the brush contact strips.

Ensure the chosen location for the decoder will be clear of the tender body and this place where its being fitted has a layer of PVC insulation tape over any metal chassis. Use a self adhesive double sided sticky pad to hold the decoder in place. Cut off or roll up all the remaining wires (These aren’t used on Steam outline models normally) and tidy the four other wires into a neat bunch ensuring they wont foul the tender top or any motor drive gearing etc.

If the loco runs in the opposite direction to the controller setting, reverse the two wires (Orange & Grey) on the brush strips.  

All this sounds quite daunting, but really its fairly straight forward!

Class J94 0-6-0 Tank Loco  This Hornby model is quite a simple conversion. I had a spare Bachmann one function decoder so this is what's being installed.  Having removed the two underside screws located either side of the cab and then the chimney screw and chimney, place all screws removed carefully to one side.  Unscrew the two screws retaining the large weight block and lift off weight. Remove the four screws securing the front and rear motor retaining plates. Lift motor and attached wires clear of body. Unsolder the top and bottom motor wires from their motor connection tags.   Cut off at the edge of the circuit board on the decoder the two unused lighting wires (Yellow and Blue) If you're using a three function or more decoder then there will be other wires to cut off too. You should only have the Red, Black. Grey & Orange wires left.  Strip a couple of millimetres of insulation off from each wires end and twist up their ends and tin with solder. Slip a length of heat shrink tubing onto the wire going to the motors top connection (Orange in my case but may be the grey wire) and solder the orange and grey wires to the motor tags. NOTE: As the loco chassis is all plastic on this model no sleeving is needed for the bottom tag/wire joint. Slide the tubing down until its over the tag and any bare wire and then apply the tip of the soldering iron carefully to shrink the tubing over the joint. Slip a piece of heat shrink tubing over the red and black decoder wires and solder these wires to the wires removed originally from the motor. Red decoder wire to the right-hand side pick-up wire and the black decoder wire to the left-hand pick-up wire. Slip the tubing over each joint and shrink down.  Replace the front and rear motor retaining plates keeping the four decoder wires on top of the rear (cab end) plate. Visually check no wires are foul of any moving parts.  Now test the decoder on the Programming track. Now run the four decoder wires into the footplate area via the existing central notch in the footplate floor. I held my wires in place with a spot of Superglue.  If all is good then with the aid of a small flat file open up the notch in the bodywork where the firebox door is. A small notch already exists, but this notch needs to be made deeper to allow the four wires to pass into the cab. Do this filing carefully and check frequently to see if the cab fits correctly onto the footplate. Once correct, refit the body with the two screws and the chimney screw. Carefully work the decoder into position against the rear cabs wall. using a spot of superglue hold the decoder in place. Tidy the wiring in the cab and retest the loco on the track. If its wished, the decoder and the wiring can be given a covering of mat black paint to help hide it. Add a driver and fireman and jobs done!

Bachmann split chassis locos are a little more difficult to convert but here's the basics....

Firstly, I only recommend the use of the Lenz or TCS range of decoders for these conversions as they have excellent fine tuning characteristics and seem to match the Bachmann older can motors well. Other decoders may well be equal or better, but I happen to like these. The final choice must of course be the end users.

Secondly, some time should be spent on deciding the exact the location of the decoder in the loco. Space inside most Bachmann steam outline locos is at a premium! Cutting away some of the locos chassis block isn’t one of my favourite options! Though it can be done with care.

Generically to fit a decoder, you have to strip the loco right down and open the chassis up into two halves, place all the items removed in a container until needed for reassembly. Now remove the motor and worm cog assembly and solder onto the motor tags two fine insulated wires. Place a small length of heat shrinkable tubing over the tag and soldered wire and shrink down so as no exposed metal of the tag or any uninsulated wire is visible.  

Now drill two 2mm dia. holes in a place somewhere on the outside of each chassis half and slowly screw in two small (e.g. 2.2 x 6.5mm) self tapping screws. Screwing in half a turn, then undo a quarter turn, continuing on like this until they are driven fully home. You have to carefully choose a place on the chassis so as the small screw heads won’t foul the bodywork when it's replaced. Often on top or at the end of the chassis block will have a clearance space, but do carefully check. Ensure all drilling swarf is removed.  Having screwed the self tapping screws right down now unscrew them a couple of turns.   Before refitting the motor back into the chassis, place a sliver of insulating tape onto each half of the chassis covering the area where the motors wiring tabs sit. 

Carefully reassemble the chassis, ensuring the plastic spacing washers are all in place over the plastic tubes that protrude through the inside of one chassis half, it is into these tubes that finally the chassis securing screws will locate and pull up the two chassis halves. Checking all the time nothing is being trapped or causing binding. Then test with the aid of a buzzer or multimeter set on its ohms range that there is no connection between the two chassis halves, nor is there any contact from either chassis half to either of the two wires previously attached to the motors tags. If all testing is ok, connect the two decoder wires to the self tapping screws by looping the stripped end of the decoders red wire clockwise under the right-hand self tapping screws head and drive the screw down until the wire is trapped firmly against the chassis. Then do the same with the black decoder wire under the left-hand screw. Finally cut to the length required, strip and joint the two wires coming from the motor to the Orange and Grey decoder wires and then solder them, covering the soldered joints by using a short length of heat shrinkable tubing previously placed onto each wire before twisting and soldering the joint.

Test the decoder by using the DCC Programming track. If all is well then whenever possible secure the decoder to the chassis. The chassis being previously covered with some PVC insulating tape in the decoder’s fixing area, or alternatively locate the decoder somewhere inside the locos plastic body. Use a double sided sticky pad to hold the decoder in place if possible.  Carefully replace the body checking all the time no wires are being trapped or are going to foul any moving parts

In one of my loco’s there just wasn’t anywhere to locate even the smallest of decoders in the locos body (an old J39), so I opted here to place the decoder in the locos tender and run four fine wires between loco and tender. This means the tender is permanently coupled to the loco and the four wires where they pass between loco and tender were painted matt black and become virtually invisible.

The conversion process above show an old Bachmann J72 tank loco which has been proven to run well on dc. In Photo P29 the body has been removed prior to any conversion work to try and find a suitable place for the Lenz Standard decoder.  Photo P30 shows the final location of the decoder, inside the cab roof, this is due to there being no space whatsoever in the main body!  Photo P31 shows the two halves of the chassis. Photo 32 shows the self tapping chassis connection screws fitted.  Photo P31 shows the decoder wires connected to the motor and terminals covered with heat shrinkable tubing. In Photo 32 the decoder has been wired (No prizes given for spotting the incorrect wiring to the chassis - Red & Black are on the wrong side facing forward [corrected after this photo was taken]) also note that the three 'Function' wires on the decoder have been completely removed, as they are not needed on this loco and if left in place would only add to the bunch of wires inside the cab!  Photo 32 shows the loco being tested and set up on the rolling road rather than on a programming track (The rolling road is connected to the programming track by a short lead and croc clips). While Photo 33 shows the body refitted and the loco being fully set up and tested on the rolling road. before being used on the main line tracks. - Spot the decoder or it wiring!

CV settings. Configuration Variables (CV) control the way the decoder acts and  then controls various functions within the loco. These are set to your own needs and to suit the locos performance etc.  Note; not all CVs are available in all decoders and some consoles may not offer the ability to configure them individually.  The list below gives the general overview of those CVs mainly available. Note; that the NMRA also specify to the decoder manufacturer that some CVs should always be  available i.e. mandatory (M) while some others are either optional (O) or recommended (R) . For a more detailed list visit the NMRA site and see table 1  NMRA Standards pdf