Original page created on 24/10/2015.
Printed circuit boards
Here is the list of printed circuits to be provided:
- LED light strips replacing incandescent lamps;
- A board for powering the bicolour LED front lamps;
- Same thing for the lamps of the trailer;
- A support for the trailer LEDs (for the motor car, the LEDs will be fixed directly on the cab);
- A four-pole electric coupling between motor car and trailer.
As always, I wish to maintain the independence between chassis and body, in order not to risk tearing out the wires during a disassembly. Exception: in the motor car, there is an electrical connection between the chassis and the cab, which is more or less attached to the body. But a removable connector is provided, and the cab may be glued to the chassis; it is only necessary to pay attention to the introduction of the frontal lamp light guide during an assembly.
Wiring diagrams and PCBs
After a careful plotting of the dimensions, by direct measurements and photographs: pitch of compartments, distance between the lamps and between the fixing points, etc., I made a PCB blank test on paper; this test allowed me to notice that one of the light strips was too short and cantilevered. Here I give you the result of my cogitations (diagram and printed circuit). The circuit is theoretically to scale, but the printer may slightly change the dimensions, which would not be dramatic here. You will be able to check the printed result thanks to the circuit dimensioning.
The resistor values are to be adapted to the available LEDs, and to your tastes as to the lighting intensity. Personally, I am rather a supporter of discretion.
You will find further the references of the components used.
Lighting strips
A detail to note: the lighting of the motor car requires two LEDs less than the trailer, but, for the other six, the circuit is exactly the same: it is therefore possible to etch the trailer circuit twice, and not mount two of the LEDs for the motor car, or even cut the useless part, which could hinder the decoder installation.
Setting the lighting strips
Since the strips are narrower than the original ones, supports must be prepared. These are made in 0.5 mm thick Evergreen, in the form of rectangles whose width is that of the interior fitting notches.
For the trailer, given the great flexibility of the interior fitting, it is better to glue the strip at only one end, to leave all the necessary backlash.
Motor car tail lamp LEDs
The lamps LEDs are embedded into the cab. Therefore, due to the very narrow space, it is not possible to wire them with a conventional insulated wire, even very thin. I therefore choose ⌀ 0.1 varnished wire, already used for the lights of my 63888 Roco.
Each LED is equipped with three wires: one common positive, one for white light and one for red light. These six wires in total are connected to the board installed into the cab (next picture).
Cab board
This circuit board includes the lamps LED resistors, plus an LED circuit for the upper front light, for which I found more practical to keep the light guide. This LED is reversed, i.e. the light-emitting part is oriented towards the epoxy plate, drilled at this point for the light to pass through. Why this apparent complication? This is to keep the copper side accessible, to facilitate connections with the LEDs and decoder. Attention: a PLCC LED is not suitable for this arrangement.
Intervention on the original printed circuit board
The purpose of this intervention is to connect the decoder to all circuits: lamps, lighting. I remind that originally only the front lights were controlled. There is no modification on the circuit itself, only the lamps are removed, and several wires connected. Note that for the wires, I follow the NEM / NMRA colour conventions.
From left to right, we find:
- The 2.54 mm pitch connector that connects to the cab board. Its three wires are soldered to the old bulb places;
- The red and black wires soldered to the pads receiving the front bogie wires. They will be connected to the rear bogie;
- The yellow, green, white and blue wires soldered respectively to terminals 2, 3, 6 and 7 of the decoder socket - detail opposite;
- 0.2 mm thick brass wire guides held by the board fastening screws, to prevent the wires from rubbing on the flywheel — yes, a piece of adhesive tape could have done the job!
- Completely to the right, the blue, green, yellow and white wires end up on pads made of self-adhesive copper tape. It is not mandatory: the wires could continue in one piece to the rear to be connected to the electrical coupling.
Wiring of the motor car
As already seen, the wires leading to the rear run through grooves milled into the chassis. They are held in strands with pieces of heat-shrink tubing stuck to the chassis bottom with thick double-sided adhesive. Thus, if necessary, a wire can be easily changed.
The red and black wires are connected respectively to the black and brown wires of the rear bogie pickups. The soldering is protected by heat-shrink tubing actually shrunk. The other wires pass under a chassis rib, then are glued (Kristal Klear) to the drawbar (gluing to be done only after soldering the wires on the coupling). A priori, there is no risk of hanging either with the transmission or with the drawbar itself.