Bachmann Class 158

Fitting a DCC Decoder to the Bachmann Class 158 DMU

Bachmann's Class 158 DMU has been around for a good few years now, giving dependable service on hundreds of layouts. It isn't DCC-Ready, so the decoder needs to be hard-wired in, but it's a fairly straightforward job that should offer no difficulties even for the novice. The LED lighting, however, needs a little more thought, as Bachmann use a pretty basic arrangement which just isn't going to work with DCC unless you make some modifications. You also need to deal with the lights in the unpowered vehicle, so the project as a whole is a little more involved than a typical loco installation. But all of the individual steps are simple enough, there's just more of them.

Step by Step

Photo 1
The workbench will be a little more crowded than normal for this project as you'll be working on the unpowered trailer as well as the powered car. In this case I've chosen the Lenz LE1024A (seen with the ubiquitous double-sided sticky pad) to control the whole 2 car set, including the lights in the unpowered car. On top of this you'll want the normal odds & ends including a cross-head screwdriver, a pair of cutters, a scrap of circuit board, your soldering outfit and a craft knife or wire stripper. If your DMU is a new one then it's probably a good idea to test-run it before proceeding, in order to check everything is OK.

If you want to control the lights in the unpowered vehicle with a separate decoder, you'll also need a Lenz LF100XF function-only decoder, although that's not something I'm covering here.

Photo 2
The body of the powered car is secured by two screws. Undo the screws (circled in red in the photo) with a cross-head screwdriver first of all and keep them somewhere safe. Not suprisingly you'll need them to secure the body once you've finished.

Photo 3
The body should unclip from the chassis fairly easily, a couple of fingernails in the join is normally all that's needed to part them. Lift the body off carefully, though, as there's a fragile plug/socket arrangement inside that takes power to the lights. Unplug this and put the body aside.

Photo 4
Unsolder the wires from the motor terminals. There should be two wires on each side, but note that they're not always the same colours as in this example.

Photo 5
Rather than use bare wire connections I always connect my decoders to a piece of stripboard (product code FL17T from Maplin) as seen here stuck in place with a double-sided sticky pad. Although this isn't essential I find it makes life easier if I want to carry out any alterations later on - especially when fiddling around with lights.

Solder two short lengths of wire from the motor terminals to two separate tracks of the circuit board as in the photo. I've used grey and orange here in order to stick with the standard DCC colour scheme.

Photo 6
Solder the two red wires from the pick-ups on one side of the vehicle to one track of the circuit board as shown. Finally solder the two black wires from the pick-ups on the other side to another track. Note again that they may not be the same colours as seen here, they do tend to vary from sample to sample.

Photo 7
I've glued an offcut of Slater's Plastikard to the top of the seating in order to provide a convenient mounting point for the decoder. This isn't absolutely essential, but I find it helps to keep the wires away from the mechanism

Photo 8
Now solder the four main wires from the decoder in place, you'll see I've shortened mine considerably to keep things tidy. The red wire needs to connect to the same track as you used for the red wires from the pick-ups. Similarly, the black wire should be connected to the track used by the black wires from the pick-ups. Next, solder the orange wire to the track used by the orange wire from the motor, and the grey wire to the track used by the grey wire from the motor.

Photo 9
The remaining wires can be soldered individually to the spare tracks on the circuit board. It doesn't really matter which wire goes where as long as they're all kept separate. Finally, stick the decoder in place with the supplied sticky pad. At this point it's as well to check that everything is working before tackling the lights or putting the body back on the chassis. The safest way to do this is to put the chassis on the programming track and try to read information from the decoder - the instructions for your particular DCC system will tell you how to do this. If all is well then you might also like to test run the chassis on your layout.

Photo 10
If you don't want to deal with the lighting at this stage then that's not a problem. It can be safely left for another day, the only problem will be that all of the LEDs will be illuminated at the same time. So if you're itching to run your newly converted Class 158 on your layout then reconnect the lighting wires, fit the body back on and secure it with the two screws.

Lighting the Powered Car

If you want to have functional lighting under DCC, read on. The following instructions give you the simplest form of directional lighting with the minimum amount of work. This method is ideal for novices as it uses the existing resistors fitted by Bachmann and leaves the actual lighting board unaltered - handy as it's awkward to get at, yet alone remove.

Photo 11
The first step is to disconnect the small resistor circuit board at the front of the chassis. Lever it up with the tip of a screwdriver until it comes away.

Photo 12
Unsolder or cut away the two wires at the rear of the board. These are the ones that lead down to the pick-ups, so make sure you disconnect the correct ones. You don't want to interfere with the other two wires as you still need to use the little black plug for the lights. Once the two pick-up wires are disconnected you can remove the board and put it to one side. If you look underneath it you'll see the two resistors that prevent the LEDs from burning out - these are a vital part of the circuit and will be kept.

Photo 13
Undo the screw that holds the bogie in place. This will let the mechanism droop just enough to give you access to the other end of the wires.

Photo 14
Snip off each of the vertical wires as close to the pick-ups as you can get. It's vital that you don't disconnect the other horizontal wire as it's needed to collect the power, so take care. Replace the bogie and secure it with the screw, leaving a little slack so the bogie can rotate freely. Press the small circuit board back in place and...

Photo 15
...wire as shown. Solder a short piece of blue wire between the two points at the rear of the board. Solder some longer lengths of blue, yellow and white wire to the locations seen in the above photo.

Photo 16
The other ends of the blue, yellow and white wires should be soldered to the tracks of your circuit board corresponding to the blue, yellow and white wires from the decoder. That's all you need to do to get the lights working in the powered car.

Photo 17
If you temporarily connect the body and chassis together using Bachmann's plug and socket, you should be able to place the vehicle on your layout and operate the lights. Make sure that you can switch them on and off from your controller and that the red and yellow LEDs are alternately illuminated when you change direction.

Lighting the Trailer Car

Photo 18
Remove the body from the trailer car by undoing the two screws in a similar fashion to the powered car. The body is connected to the chassis using a plug & socket arrangement once again. Carefully lever the resistor circuit board away from the chassis - there's a good chance that it will be firmly glued in place so don't be suprised if the two blue locating pegs actually snap off. This is fairly normal and isn't a problem.

Photo 19
Flip the circuit board up and snip off the two resistors using some Xuron track cutters or similar implement. Be careful not to damage any of the four wire connections to the board as these are still required. Removing the resistors is a quick way to break the existing circuit and separate the LED lighting from the track pick-ups.

Photo 20
Replace the circuit board, gluing it in place if you had to snap the locating pegs to get it off in the first place. Drill a hole through the interior wall behind the circuit board to allow the new wiring to pass through, and do the same in the other interior wall at the rear of the vehicle.

Optional: Given that you can never have too many pick-ups, now would be a good time to utilise the ones in this vehicle for reasons of more reliable running. You don't have to do this, but while you've got the vehicle apart it's very easy and is strongly recommended. Just solder a red and a black wire in place as shown, threading them through the hole in the wall. Make sure the wires are long enough to make a connection with the circuit board in the powered vehicle.

Photo 21
To deal with the LED lighting, solder a white and a yellow wire in place as shown, threading them through the hole in the wall. Make sure the wires are long enough to make a connection with the circuit board in the powered vehicle.

Connecting the Two Cars

Photo 22
For purposes of illustration only, the above photo shows where the yellow and white wires are connected in both cars. Obviously much longer wires are used in reality. If wired as shown, the lights will work correctly, with the front and rear lights illuminating according to the direction of travel. It is essential that the connections are made as shown if the LEDs in the trailer car are to be protected by the resistors in the powered car. Don't be tempted to wire the long yellow and white wires from the trailer car directly to the decoder or it's associated scrap of circuit board as the LEDs will receive too high a voltage and burn out.

Photo 23
Again, purely for the purposes of illustration, this photo shows where the red and black wires are connected in both cars. Obviously much longer wires are used in reality. Basically all of the pickups on the black side of the DMU are wired together using this arrangement, as are all of those on the red side.

Photo 24
The easiest way to join the two cars electrically is simply to drill a hole in the end of each and run the wires through, leaving enough slack for the unit to go around curves. This is very effective, but can be unwieldy when transporting or maintaining the unit.

Photo 25
Alternatively, some kind of plug and socket arrangement can be used so that the two vehicles can be separated for easier storage and transport. There are many products that can be pressed into service for this purpose, different people will have different preferences. Lately I've got into the habit of recycling the NMRA plugs cut from DCC decoders when doing hard-wired installations, purely because I've got them kicking around and the soldered joints are better than anything I tend to manage.

The matching sockets can be made from socket strip (Maplin product code DC17T) but in this instance I've used a cast-off circuit board from a Proto 2000 GP30 loco - again purely because I'd got some lying around. One of these will fit nicely into a hole cut into the corridor connection as shown, and there are even solder tags ready for the wires. This method works very well, although you need to keep an eye on curve radii - especially on crossovers.

Miscellaneous Debris

Photo 26
The preceeding photo sequence shows you how to wire the Class 158 for simple directional lighting only. If you want anything more sophisticated, such as individual control of lights, then you need to get at the actual LED circuit board which is firmly embedded in the cab end of the body.

The easiest way to remove this board for modification is to cut through the central pillar (marked with the red arrows in the photo) using some Xuron track cutters or similar. The tips of the LEDs will hold it in place reasonably well when you put it back, but if you want something a little more secure then simply glue some scrap plastic into the gap marked with the green arrow.

Photo 27
At some point in the future I'll be adding a page detailing how to incorporate more advanced lighting into these units, but for now the above photo offers some basic clues.

Photo 28
An attractive option worth considering is fitting door warning lights using some of the tiny LEDs that are available from Express Models.

Photo 29
This extra lighting obviously needs a little more wiring, but nothing too substantial. Again, I'll add details for these modifications in the future.