Rebuilding Northlander Express train, Märklin 37500,  with mfx sound decoder

Updated 03.03.2013

The NS/SBB RAm TEE I train set has always fascinated me, since I saw the 3070 at a remote friends layout many years ago.  When I saw the Canadian Northlander version, from Ontario Northern Railway, with a GM FP7 diesel electric locomotive, I just had to buy it.
Some information about the prototype from Modellbahn

Why rebuild a rare model?
The original decoder has a fault after a short circuit (made by me), so I decided to replace it with a mfx sound decoder, including all the original functions, and add some extra.

Märklin 37500

The Märklin 37500 set was manufactured in 1998 with numbered certificates in a limited number.  Max. 5000 sets for sale in Germany and max. 2000 sets for export.
My set is no. 1969

The locomotive:

This photo shows the 37500 locomotive before the conversion

The original c91 decoder:

I removed the "coil" in front of the decoder and connected the red wire to the relay directly to the pick-up shoe contact plate.
A similar "coil" was removed from the control car.

Two capacitors, connected between the brush holders and motor ground, must be removed from the motor

The locomotive inside after the conversion:

The modified motor:

The only difference is the removal of the two capacitors.

The mfx sound decoder, ESU V4 M4, no. 64499, is installed on an amplifier board 51968, to be able to use the f3 and f4 outputs to control a bi-stable relay to change between the pick-up shoes according to the driving direction.
ESU has a special 21mtc decoder board for the pick-up change, but as I have many suitable bi-stable relays, I wanted to do it "my way".  As far as I know, the function of the ESU board is the same as I have with my relay.  Sound project is ESU 64436
Basically, I prefer to use Märklin products in my Märklin locomotives, but sometimes I have to used parts from other manufacturers.  I use the ESU decoder due to the programmability and the available locomotive sounds.

The decoder functions
direction Item
f0 f0-f forward front light, locomotive
f0-r reverse front light, control car
f1 f1 both interior light in the connected cars
f2 f2 both light in driver's cabin
f3 - both driving sounds
f4 - f15 - both other sounds
- f3 forward activated by drive forward

The 3-f and 4-r function
outputs control the
pick-up shoe changing
bi-stable relay

activated by stop forward
- f4 reverse activated by drive reverse
activated by stop reverse

Pick-up shoe directional changeover:
This train set has originally a c91 decoder and a sound unit.  In addition to changing the direction of the motor and the lights, the decoder also changes the pick-up shoe, as it has one in each end of the train.  This way it always picks up the current from the front end according to the driving direction. I wanted to keep this function.

When changing direction of the train, the function outputs f3-forward or f4-reverse connects to one of the two coils in a bi-stable relay, according to the direction.  the same function can be achieved with ESU's 21mtc circuit board for directional pick-up change, 51966, but I wanted to use a relay I had in stock.
See the wiring diagram at the bottom of this page.

Locomotive front light
The front number plates is illuminated by the dame bulb as the front light.  I found them a bit too transparent and difficult to read,  Therefore I covered the inside of the numbers with plain white copy paper, as a light diffuser.  The Scotch tape does not stick very well to the surface, so I have to find a better way to fix the paper.

The result

The cars

Electric connection:
There are four wires running through the train:
1, red wire: Current from the rear pick-up shoe to the changeover relay
2, brown/red wire: Current to the interior light, from the decoder
3, yellow wire: Current to the white front light in the control car, from the decoder
4, orange wire: Common + to all the lights in the train, from the decoder


Car A, the compartment car, running behind the locomotive:

A lot of passengers are missing

Car B, the restaurant car in the middle of the train:

Still one free table in the restaurant and no chef in the citchen.

Car C, the control car:

Some people have to be seated here

Wiring diagram, 37500:

Some facts about the GM FP7 locomotive, from and Wikipedia:
Power type Diesel-electric
Builder General Motors Electro-Motive Division (EMD)
General Motors Diesel (GMD, Canada)
Build date June 1949 – December 1953
Total produced 381 (324 by EMD, 57 by GMD)
For ONTC 22 by GMD, road numbers 1500 - 1521
from March 1951 to October 1953
Wheel arr. UIC = Bo'Bo'
Gauge 1.435 mm
Length 16,66 m
Weight 117 tons
Fuel capacity 4.542 l (?)
Main engine EMD 567B (567 cubic inch per cylinder)
Cylinders 16, in 45O V-shape
Bore & stroke 216 x 254 mm
Displacement 148,66 l
Rpm range 275 - 800
Power output 1,500 hp (1,100 kW)
Main generator GM - D12D
Traction motors 4x GM - D27 electric
Wheel dia. 1.016 mm
Max. speed 105 km/h
Brakes Westinghouse air brake
Dynamic brake
Multiple units Possible
Partly converted to metric by me, no warranty for correctness.