coversion of marklin 3709 br 85 steam locomotive

Tip: 60921 Upgrade Conversion of 3709 Steam Locomotive Date: 12-08-2008 Updated 31-03-2012 Correction 20-05-2014

http://members.ozemail.com.au/~rossstew/rms/marklin.html 1

Hi All,

I decided to upgrade my friend Johns 3709 locomotive to have controllable functions using the Marklin

60921 mfx decoder. The locomotive by default used a 6090 decoder and the F0 light function was used to

switch both telex couplers leaving the lights and smoke option always switched on.

The 60921 MFX decoder has the usual F0 function for lights and two extra functions F1 + F2 which I

chose to use to switch the telex couplers and smoke unit.

Warning: - The size of the 60921 is smaller than the old 60901 decoder and as a result of this the function

outputs have reduced capability. Marklin states 150mA for each function output. In the instructions

Marklin states that two telex couplers can be connected to the one function output. They should have

stated the type of telex couplers as the telex couplers on the 3709 locomotive require 165-170mA for each

telex.

To overcome this problem I wired a Nais TN2-12V relay to switch the two telex couplers together

controlled by F2, it was glued to the existing bracket with hot melt (see red arrow). I used F1 for the

smoke function.

The upgrade conversion was very straight forward. I used a cable tie to hold the decoder on to the

existing support bracket and programmed the decoder using Johns ECoS.

On testing the locomotive I discovered that the smoke unit didnt smoke all the time. The body shell is

only held by two screws which allow the drive wheels to move within the shell as it goes around curves.

Because of this movement the electrical connection is interrupted.

I solved this problem by using A

Marklin solder lug wired to the

ground connection of the

locomotive (see yellow arrow)

With the body shell fitted the

screw holds the solder lug

firmly against the shell making a

very good electrical connection.

The photos above show the original light bulbs being used.



Hello All,

I decided to improve this locomotive by converting to warm white LEDs for the lighting and add a

further two chassis ground connections to improve the running.

I also noticed that I needed a schematic diagram, so at long last here it is.

Schematic Diagram

The 1k resistors are soldered in line with the connecting wire and covered with heat shrink. The 1N4148

diodes are shown in the photos on the following pages.

Front and rear view of the locomotive

with warm white LED lighting.

Part Number Supplier Description Quantity

934-1102 Element14 1K MF25 Resistor 0.25W, 1% 2

120-0956 Element14 Nais TN2-12V Relay 1

102-3035 Element14 Harwin SIL Socket 32Way D01-9973242 1

108-1177 Element14 1N4148 Signal diode 3

PLCC2LW3CT Ledz.com PLCC2 warm white LED 1

330PWO4C Ledz.com 3mm warm white LED 1

1k 1k

60921 F1

F2

Telex Front

Telex Rear

1 1

10

3

4

2



Led Lights and Telex Diodes The front light LED (red arrow) is a PLCC2 type

soldered to cut off resistor leads and plugged

into the existing light socket.

The grey arrow shows a 1k resistor soldered in

line with the grey wire and covered with heat

shrink.

The yellow arrow shows the cathode of the

Telex diode connected to the centre rail red wire.

The rear light LED (green arrow) is a 3mm round

type plugged into the existing light socket.

The yellow arrow shows a 1k resistor soldered in

line with the yellow wire and covered with heat

shrink, it connects to the cathode of the LED.

The orange +wire connected to the LED anode as

shown in the photo.

The yellow arrows show the location of the Telex diodes for the front and rear Telex couplers. The anode

is connected to the chassis ground and the cathode is connected to the Telex coupling wire, refer to page 2

for wiring schematic.



Relay Connections for the Telex Couplers

The connections (yellow rectangle) are the violet common connections in the schematic diagram page 2

from pin 4 of the relay to the Telex couplers front and rear.

The brown/green wire connects to pin 10 of the relay and is the F2 function from the decoder.

The orange +wire connected to pin 1 of the relay.

The red wire on pin 3 of the relay connects to the anode of the diode covered with heat shrink (see page 2

top yellow arrow)

All wire connections to the relay pins use the Harwin rolled pin connectors soldered as single sockets and

protected with heat shrink.

Extra Chassis Ground Connections

The blue arrows show where I have wired extra chassis ground wires to overcome the paint which acts as

an insulator around the mounting screw on the pony trucks.

As always enjoy your hobby.

coversion of marklin 3709 br 85 steam locomotive

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