Equipment of the driving coach

Here is the continuation promised for already more than five years. I was expecting a possible need for disassembly. It happened, because I noticed that the anti-flashing capacitor became insufficient with the eight coaches in the complete train. It has a capacity of 1000 µF for an operating voltage of 35 V. However, the capacitor size depends on this voltage. With 25 V, we have a capacity of 2200 µF for the same size (ø 13 × 25 approximately). The space available in the coach’s technical room, as we will see, allows the installation of two 2200 µF / 25 V capacitors in parallel, which in practice will quadruple the present capacity.

The original structure

Originally, a space was provided in the cab for a decoder. The printed circuit is not satisfactory, as said on page 1. In addition, to hide the wiring as well as possible, we will see that I have had to free up the space in this cab as much as possible. To accommodate the decoder and the capacitors, I found that the central technical room was particularly suitable, provided that it was enlarged as much as possible.

Structural changes

In addition to the platform equipment, which doesn’t differ from that of other coaches, there are a number of modifications to be made.

Interior fittings

An approximately 13 × 13 mm hole is made under the cab; it allows to put a connector in, as we will see later.

To enlarge the technical room’s space, the central part of the lower fittings is cut out. Naturally, as for the other coaches, but all the more here, the upper fittings are glued on the lower at the level of the stairs, taking great care to respect the distance between the two separated halves. The best for this is to glue with the parts mounted on the chassis.

Note the power connector of the light strip.

Opening in the fittings

Opening in the technical room


The ballast is cut in the technical room to leave a free space of about 10 mm, necessary for the future passage of the wires. The remaining visible part is insulated with electrical tape.


There is little to do. In this coach, exceptionally, the 2nd floor lighting strip will be stuck under the roof. It is therefore necessary to level off all the reliefs therein.


As previously reported, the original light guides are too small. They are replaced with 2 mm dia. “cannon” LED sections (we can also use Krystal Klear). The LEDs themselves will be SMDs.

Electrical modifications

Note: all the following circuits are obsolete, see the section Design change below.

Current pickup

As the driving coach powers the whole train, the current pickup should be the best possible. So the use of conductive bearings and middle-insulated axles is essential. For this, we must get uninsulated wheels from other coaches and exchange them with the insulated wheels. Attention: the wheels are not very tight on the axles, which are themselves of poor quality (badly machined tips). The distance between tips is reduced from 24.8 to 24.0 to take into account the thickness of the conductive bearings. Each wheel is therefore offset 0.4 mm outwards.

The conductive bearings are manufactured with 2/10 mm brass sheet according to the technique already used for DEV AO REE coaches.

Conductive bearings

The wires from the bogies pass through the chassis grooves, under the ballast, and meet in the technical room.

Note the wire colour not conforming to the NEM standard (it should be red instead of blue), but I preferred to keep the original wires.

Wires coming out of the bogies


The lower strip is the same as for other coaches, with less unnecessary LEDs, but it is powered directly in the technical room, with a two-pin 1.27 mm pitch connector.

The upper strip is very similar to the others; I added a cab lighting LED, which will have a special connection.

This strip, as already said, is stuck under the roof. I have provided a connector which will facilitate the separation between body and chassis. This connector must be able to be disconnected before dismantling and therefore be accessible from the outside. This is why I planned the square opening of the cab layout.

Cab connectors

This 1.27 mm pitch connector has five contacts. In order, V+ (blue); red lights (yellow); white lights (white); compartment lighting (green); cab lighting (purple). The male contact soldering is protected by a heat-shrink tubing; the female contacts are soldered on a small PCB, because they are quite fragile.

Head lights

The PCB is completely remade, with SMD components. The LEDs are mounted reversed.

Head light circuit

Note: I first tried to mount cannon LEDs, a priori easier to implement, but they come up against the cab layout and therefore cannot be placed perfectly horizontally.

Power circuit and decoder

For the moment, as already said, this circuit has only one capacitor of 1000 µF, insufficient. The decoder is next to it. Some of the latter’s wires leave directly for the cab along the ballast.

Present power circuit

The black/silver wire is soldered to the decoder’s ground. It will be connected to the negative pole of the capacitors. Thus, all circuits will benefit from anti-flashing, and not just the compartment lighting, as it is currently the case.

Present power circuit

Here is where this wire is soldered. It goes without saying that this only applies to the Lenz LF101XF decoder, which is no longer manufactured.

Decoder’s ground location

Here is the new planned circuit, the realization of which will wait for better days.

The capacitors are arranged lengthwise and no longer crosswise.

The decoder will be stuck on a vertical wall.

New circuit project

The better days have come. Here is a sample of the circuits received from JLCPCB. From left to right: two lighting strips for the lower floor; two energy tank circuits, one of which is equipped with its two 2200 µF capacitors; the light circuit.

View of the new PCBs

Note: at JLCPCB, the PCBs must be ordered by five identical. This is not a problem for the light strips (I need eight of each type, I will have two extra!). For the other circuits of which I only need one copy, I have four useless left! It’s not a big deal considering the moderate price. But if you’re interested, let me know at the address listed on the home page. Please note: these circuits are bare, without components, to be assembled by yourself.

Design change

I decided to completely redo the wiring. Indeed, having placed the decoder in the technical room was not necessarily a very good idea: it required unnecessarily passing wires under the interior fittings, in particular those of the white and red lights.

So, it is better to place the decoder in the cab. However, this one has a double rear wall, with a space a priori a little too narrow for a decoder, but which becomes sufficient by levelling the internal reliefs (between 2.5 and 3 mm). The decoder is installed vertically. Most of the wires come out down where there is an opening that just needs to be enlarged a little. Some wires, feeding the upper floor and cab lighting, come out upwards.

For the remaining connections between the two ends of the coach and the technical room, I had the choice between three solutions:

View of cab with decoder

View of cab with decoder

I chose the latter solution. But, as it was not planned at the beginning1, I simply milled an epoxy plate to obtain parallel tracks. Since I engraved this circuit before I decided to put the decoder back in the cab, I unnecessarily milled seven tracks, when only five were needed. Better too much than not enough… Here are all the parts to assemble.

1. Besides, if I had thought about this solution earlier, I would have made a single circuit combining the front / rear links and the capacitors. It could have been 0.4 mm thick to facilitate its installation under the interior fittings.

Set of parts to be assembled

Hover over the picture for a larger view.

From back to front, we can see:

A blank assembly ensures that the total thickness will not prevent reassembly of the interior fittings.

Blank assembly

Note: if this thickness is a problem, you can safely remove the ballast plates. Indeed, the weight will then drop from 172 to 148 g, which is the maximum value recommended by the NEM.

Interior fittings

To compensate for the thickness of the components of the lower strip, I glued on each side a polystyrene strip, section 0.5 × 3 (2) with Uhu Strong glue, then the whole under the upper deck with Faller Expert plastic glue. On both sides, I put white self-adhesive paper (1). It would have been better to paint the strip white. Here, it is painted silver.

Then, I glued the partitions under the upper deck by interposing 1 × 1 polystyrene strips (3), to get the same ceiling height everywhere. The resulting assembly is now quite rigid.

Interior fittings

Equipment of the body

After connecting the decoder wires to the upper strip, the cab layout is put back in place then the strip is stuck under the roof.

Installation of the upper strip

The light circuit is connected to the decoder.

Connection of the light circuit

Then it is lightly glued in place with Kristal Klear.

Gluing of the light circuit

Finally, a 1.27 mm pitch five-pin male connector is soldered to the remaining wires of the decoder. These wires are:

Decoder connector

Note that the header is reinforced with a very small PCB. Indeed, the insulating body of these headers doesn’t withstand well the soldering heat and doesn’t properly hold the pins. It would even be possible to remove this body after soldering to gain a little bulk.

Various connections

Engraved circuit with capacitor circuit. The front end of the circuit receives the female connector matching the decoder’s:

Engraved circuit connections

Rear electric coupling. The two wires are held together by a mini wrapping wire tie to avoid their fatigue in the solders:

Rear coupling connection

Bogie connection, not photographed.

Reassembly and functional test

The interior fittings are reassembled on the chassis. We just have to avoid getting wires caught between the two parts.

Reassembly of the interior fittings

Before definitively putting the body back in place, a functional test is essential.

Functional test

Finally, after refitting the body, the connector wires as well as the connector itself are tidied up under the cab.

Tidying the connector