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Bachmann `Class 24' dieselThis was very straightforward. This model is `DCC ready', which means that its power pickup and motor connections are brought to a convenient place, ready for the decoder to be installed. At present, few locomotives are as well-designed as this, so it is nice to fit one that makes decoder installation easy.Dissasemble the locomotive by removing the four concealed nuts in the bottom of the chassis. You'll need a long, fine screwdriver for this. Lift of the body, being careful not to lose those small nuts. On the top of the motor assembly is a small printed circuit board. This has six wires attached: the four on the corners are from the track power pickups -- these are simply connected together on the PCB -- and the two in the centre are the supply to the motor. On top of this PCB is a small eight-pin plug. You may be able to get a decoder that plugs directly in. If not, simply remove the plug and solder the decoder wires directly to the PCB. The decoder's power supply wires go to the incoming power connections (at the end of the PCB) and the decoder outputs go to the motor connections (in the centre). The Class 24 runs perfectly with a ZTC215 decoder, which costs only £15. No adjustment was necessary, which is good because the 215 does not provide for any. Hornby `Black five'The `Black five' is also DCC-ready, and has exactly the same connector as the Bachmann Class 24. The motor is in the engine, not the tender, which is quite unusual for Hornby tender engines. The engine body can be released by removing the single nut under the front bogey; this exposes the motor and the decoder connector, which is on the top of the motor assembly just behind the smokebox. There isn't much room to install a decoder on top of the decoder connector, so I soldered the decoder (ZTC214) to it with the wires about an inch long. Then, when the body is reassembled, the decoder slots into the smokebox. All in all this was an easy job: ten minutes.A certain amount of tweaking was necessary to get the engine running smoothly under DCC; in particular, I had to lower the maximum voltage to about half-way to get any low-speed control. Hornby `Gordon' 2-6-4This installation was the exact opposite of the Black five, despite the locomotives' being the same size and shape. The motor is in the tender, but there are pickups on both the engine and the tender. This means that the decoder can't be installed in the engine body -- which works nicely in the Royal Scot (below) -- where there is loads of room, but has to go in the tender, where there isn't.The pickup wires all run to two large metal tabs on the motor assembly. You'll need to unsolder these, and connect then the the red and black wires of the decoder. Then the decoder's grey and orange wires go to the motor tabs. All I can say is that the ZTC214 decoder just fits between the motor assembly and the body of the tender. It took me two hours to find a position to put the decoder that would allow the body to be refitted, without the decoder fouling any moving parts. What a drag. ZTC make a smaller decoder that the 214, but I'm told that it's won't work for this engine because the current consumption is too high. Hornby `Percy' 0-4-0This small loco was, in terms of convenience of installation, almost as bad as `Gordon'. His body is very small, so there's not much room. In addition, the motor contacts are supplied directly from metal contacts on the frame, not by wires. There's just about room for a decorder in the cab.Remove Percy's body shell by squeezing the two spring clips under his tank, and pulling the shell upwards. There is a similar spring clip to hold his motor in place: remove this and withdraw the motor. You will see the two motor contacts on the frame under the motor location, with the suppression capacitor attached. Cut the decoder wires to about 2 inches. Solder the red and black wires to the contacts where the motor would normally connect. Ensure that any solder blobs are minimized. Now put the motor back upside down. This will put the motor power contacts on top, and put the plastic cap of the motor in contact with the original motor tags. Check that the contact tags are touching only the plastic, not the metal motor can. Solder the grey and orange wires to the motor power terminals. You can replace the body while wiggling the decoder up into the cab. I had little success with the cheap ZTC215 decoder with this model: it isn't configurable enough. It does work, but it is erratic and jerky. Instead I used a ZTC203, which allows the motor drive PWM frequency to be adjusted. I found that it needed to be increased, but I can't remember by how much. The 203 decoder has auxilliary outputs for lights: Percy doesn't have any, but I fitted some `grain-of-wheat' bulbs, one at each end of the loco. These are wired with one end to the decoder (yellow for the rear lamp, white for the front) and the other end to the track pickup terminal. for brighter output, you can wire the lamps to the `common' (blue wire) instead. I guess a 214 decoder would have worked as well (as it did for Thomas), and been a lot cheaper, but I wanted lights. Airfix `Royal Scot' 4-6-0This large tender engine has power pickups on the engine wheels, and a motor in the tender. There are no pickups in the tender itself; instead all the current is supplied by two fine wires between the engine and the tender. These wires have to be broken and the decoder put into circuit. You can do this either in the tender or the engine. I prefer the engine, as there's slightly more room.First, you will need to separate the loco body from it's chassis: simply remove the screws in the chassis and pull the body gently upwards. If you pull the cab away from the engine body, you'll find a narrow slot into which you can push the decoder. If you push it wires-first, you can draw the wires out into the body itself. Cut the fine wires that go to the tender. Connect the wires that go to the wheel pickups to the red and black wires of the decorder, and the orange and grey wires to the wires that go to the tender. Hornby `Thomas the Tank engine' 0-6-0This one was a real pain. There is just room for a decoder in the `tank' area, between the motor and the body shell. A really small decoder might also fit in the cab. The big problem is that Thomas has a live frame, with the one of the motor contacts directly onto the frame.Remove Thomas's body shell by unscrewing the nuts in the bottom of his chassis. Remove the screw in the top of the motor carrier, and withdraw the motor. Note the brass contact underneath the motor carrier, and the contact on the bottom of the motor that sits on it. Use a small saw or file to make a slot in the motor carrier just above the offending contact. Then pull the contact up into the slot, so that it won't touch the frame contact when the motor is replaced. Cut the decoder wires to about 2 inch length. Solder the grey and orange wires to the motor contacts: the original one on the top of the carrier, and the new one you have made by drawing up the bottom contact. Solder the red and black wires to the two brass wheel pickups. Replace the body while wiggling the decoder into the tank space. You may have to stick it in place with tape, else it will drop down while running and foul the wheels. Like Percy, you'll need to increase the PWM frequency of the decoder to get smooth running, and reduce the maximum voltage.
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