Rebuilding Märklin 43410, SBB ABt 50 85 38-33 930-2 with a Märklin 60961 decoder

Updated 16.04.2012

Märklin 43410 and 39420

The 43410 is originally fitted with a white and red front lights, changing with the driving direction.  I was not very happy with the light installation.  The front light, either the red or the white, was on all the time.  In addition, the light changes when the car starts moving, not when the direction of the pulling/pushing locomotive is changed.  The light is controlled by a mechanical switch in the bogie.

A number of SBB cars are supposed to run in the same train as the 43410, all with interior light.  As I wish to control the interior light with a decoder and a relay, I decided to install this in the front end of the control car, as this car already has a pick-up shoe.

The originally fitted printed circuit board.  The two parts next to the car was installed in the front bogie, the orange and the black wire was soldered to the to soldering pads in the middle of the board.  The brown and the yellow wires come from the bogie in the other end of the car; the brown is "0" (wheels) and the yellow "B" (pick-up shoe).  I did not want to alter any of these parts, so I carefully removed them and store them safely.

The new printed plate, that has to be lifted one millimetre up from the floor. It is too thick to fit as the original board was fitted.

As all the parts will be installed in the driver's end of the car (front end), I moved the pick-up shoe and the ground connector to the front bogie.

New circuit board
The new board will be used for LEDs and their dropping resistors, as well as a distributor for the orange wire from the decoder (+).  By carefully aiming it is possible to find the location for the four LEDs, compared with the original circuit board.  The three white LEDs are connected in series, with a 510 Ohm serial resistor.  The red LED has a 1,5 KOhm resistor.  The interior light in the driver's cab is also soldered to the board.  The LEDs I use are a bit bigger than the original ones.  The camera did not catch the colour difference between the white (or rather yellow) and the red LED.

The relay
A small one-pole relay, that just fits under the interior, inside the area of the original circuit board, when I bent the contact pins down.  It's approx. 7,3 mm high.

Left upper pin = contact output, current to the connected cars, red wire to the current conducting coupling
Left centre pin = coil input, brown/red wire (-) from the decoder
Right centre pin = coil input, orange wire (+) from the decoder via the circuit board
Right lower pin = contact input, red wire from the pick-up shoe

A drawing of the board is in the bottom of the page.

I installed the 60961 decoder in a decoder holder, Märklin part no. 285820, on the steel plate under the interior, between the front doors.  I cut out the floor of the interior between the doors, so the interior fits perfectly over the decoder an all the wires.  The wires must be spread out flat, to fit under the interior.

With the interior installed:

The decoder functions:
f wire colour function
f0-f gray one red light at the car end
f0-r yellow three white lights at the car end
f1 brown/red interior light in the connected cars,
via the small black relay
f2 brown/green interior light in 43410, via the two-
pole connector on the board
and a 1.500 Ohm resistor
f3 brown/yellow light in the driver's cabin
f4 brown/white not connected

The light changes:

The Märklin 39420 SBB Re 4/4I 10 015, will be used as pulling power for the train set.

Interior light in the control car:
The interior light in the 43410 itself is controlled with f2, brown/green wire.  Two 73400 LED light units is used.  It gives a rather warm light colour, but I am not fully satisfied.  I experimented with a home made light unit, using 28 Volt normal bulbs.  I like this light better, but the power consumption is far higher than the approx. 30 mA the two 73400 units consume.  I soldered two wires to the 73400-connector behind the driver's cabin, and connected them to the two-pole connector on my home made circuit board.  The light colour is rather warm, but in my opinion it is too bright.  So I installed a 1,5 KOhm resistor in series with the brown/green wire (function f2) from the decoder to the light units.  Perfect.  And the current consumption went down below 10 mA.

Light to the connected cars:
The interior light in the connected cars is controlled with f1, via the relay.  I have not installed light in the other cars yet.  I will probably go for the 73400 units, except for the luggage car, where I wish to illuminate only parts of the car.
The red wire from the pick-up shoe is distributed to the relay contact and to the decoder. The other end of the relay contact leads to the conducting coupler (Märklin 7319)  in the other end of the car (single red wire under the steel plate).  The relay coil is connected to function f1 (brown/red wire from the decoder) and to the orange wire from the board.

Note: the driver's cab normally sticks to the car body.  I just removed it for examination and to cover the light guide with thin insulation tape, to prevent the driver's cab light spilling to the upper front lamp.  At the same time I glued a man to the seat.  He became a bit too tall, but I find the removal and installation of the cab rather tricky (easy to brake the light guides to the lower lamps), so I leave him as he is.

The parts I use to upgrade the Märklin 43410 SBB Abt and the connected cars:
  Märklin no. Pcs. Description
60961 1 Function decoder
456200 1 Holder for decoder
73400 2 Interior light unit
7319 1 Current conducting coupler, from set of 10
- 1 1-pole miniature relay
- 4 smd LED, yellow, front- and cabin light
- 1 smd LED, red, rear light
- 1 510 Ohm resistor
- 2 1,5 kOhm resistor
- 1 2,2 kOhm resistor
- 1 Home made circuit board
- 2 2-pole connector, cut form SIL-connector
73400 8 Interior light unit
7319 4 Current conducting coupler, from set of 10
- 4 1,5 kOm resistor
7319 1 Current conducting coupler, from set of 10
- 1 Home made light installation

Wiring diagram:

The LED circuit board looks like this:

My plan is to run the train like this:
39420 SBB Re 4/4 I 10 015 locomotive
43400 SBB D 18926, luggage car
43380 SBB B 6124, 2nd class car
43360 SBB A 2231, 1st class car
43390 SBB WR 10121, restaurant car
43370 SBB B 5581, 2nd class car
43410 SBB ABt 50 85 38-33 930-2, control car, 1st and 2nd class
I know that the control car ABt is not supposed to be here (wrong era), but I think it looks good anyhow.