Rebuilding Märklin 3068, NSB Di3b 3.641, to digital with Märklin 60924 mfx conversion set

Updated 07.06.2013

Märklin 3068
This big Diesel engine is one of my favorites. It's prototype was made by NoHAB in Trollhättan, Sweden, in the 50's and the 60's, based on a GM locomotive from USA.
The NSB Di3b 3.641 was delivered to NSB (the Norwegian State Railway) in 1960, with the factory number 2419. Initially it was meant for VR, Finland, but due to political reasons VR decided to by their locomotives elsewhere.  It has axle arrangement (A1A)'(A1A)' and is 18.900 mm long.   In 2001 it was shipped to Kosovo.  It is no longer in service.

Märklin 3068, NSB Di3b 3.641

This locomotive used to have an electro-mechanical reversing unit.  The mfx decoder form the set 60924 is installed at the same place, in holder 456200.

The installation of the motor from the 60924 set is a little bit tricky.  In the 3068 the motor bogie is installed in the locomotive frame with a U-shaped spring.  The new motor cover from 60924 is not designed for this installation method.

If the original motor bogie is used, the cover must be modified so the spring fits, by grinding and drilling. Also the circular part of the chassis holding the motor bogie is different from the newer versions of the Märklin NoHABs.  It is a bit trickier to remove and install the motor bogie in the older version, see the scratches in the motor.  These came during installation.


I solved it by using a motor bogie left over from an earlier conversion of a Märklin 3143, NSB Di3a 3.605.  I always store the removed parts, so I can build the locomotive back to it's original condition, using the original parts, including the wires.  The new motor looks like this:

The additional bulb on top of the bulb holder is just a test installation for the driver's cabin illumination.

I installed new bulb holders, Märklin part no. 624510, in the holes for the original bulbs, without removing the bulb contact tongue.  I use 610080 (22 Volts) bulbs.

Close couplers:
I have installed close couplers on all my NoHABs.  Unscrew the normal coupler and and store it somewhere.  All the other parts, like the locomotive body, bogie frame, centring spring and the screw remains as they are, without any modifications.

Take two Märklin 363950 coupler pockets and cut off approx. 3 mm of the upper part of them, as shown in the photo.

Install them upside-down (related to their normal usage), using the original centring spring and screw.  The coupler pocket in one end may be installed before fitting the locomotive body, the other must be installed after fitting the body.  The body will not fit over both pockets.  Finally insert the close coupler 70163.

My setting of the decoder:
Decoder settings, 3068 Default Mine
Analogue settings:
  Enable analogue mode check <
Starting voltage 7,300 <
Maximum voltage 23,000 <
Control settings:
  Swap directions uncheck <
Max speed 255 60
Min speed 4,000 <
Acc time 7,000 15,000
Dec. time 3,750 15,000
Forward trim 1,000 <
Reverse trim 1,000 <
Motor settings:
   Motor PWM-frequency:
Low frequency uncheck <
High frequency check <
Load Control:
Reference parameter 11,300 15,000
Control parameter K 60 11
Control parameter I 120 150
Control influence 255 <
Special options:
  Preserve direction check <
Persistent acceleration uncheck <
Persistent speed check <
Persistent functions check <

The 3068 decoder functions:
f0-f Front light end 1, changing with direction
bulb 610080, socket 624510
f0-r Front light end 2, changing with direction
bulb 610080, socket 624510
f1 Interior light driver's cabin end 1
28 Volt T1 bulb and 330 Ohm serial resistor
f2 Interior light driver's cabin end 2
28 Volt T1 bulb and 330 Ohm serial resistor
f3 Shunting speed
f4 Acceleration and braking delay cancelled

Later an mfx sound decoder was installed in this locomotive, identical to the one in 3143A, NSB Di 3.605.

Links to a lot of NoHAB Di3 prototype information: