Updated 18.05.2013
Märklin 3346, DB 236 405-7 and 406-5
Thanks to Brandon Sutter, who permitted me to use his "before disassembling" photos.
Preparation:
Start with removing everything from the locomotive chassis, from both units.
I also removed the couplers, to install close couplers
(Märklin 7205) front and rear.
Before disassembling:
From below it's no difference after the conversion, except for the close
couplers
After disassembling:
The 600190 bulbs are missing from the photo
Conversion parts:
For the 3346, which has two motors, I initially used the conversion kit 60901 for 236
406-5 and the motor from the cheaper 60760 conversion set for 236 405-7.
Before going for only one decoder for the two motors, I measured the power consumption
for the two motors with "pure DC" from an adjustable power supply. Even with one blocked
motor, the consumption never exceeded 0,7 amps. As far as I know, the limit for the
decoder motor output is 0,8 amps. So I took the risk of installing only one decoder.
After the conversion:
Motors:
Installation of the motors themselves are simple. After removing all the existing
parts (motors, reversing- and electronic unit etc.), clean the chassis and make sure
that everything (transmission and wheels etc.) is turning smoothly. Install the new motors,
without the brushes. Check once more that everything revolves effortless. Install the brushes.
The motor in 236 406-5:
Photo before rebuilding with mfx decoder
The motor in 236 405-7:
Decoder:
The mfx decoder is installed at the same place as the original reversing unit electronic
control circuit board in 236 406-5. It is installed in the decoder holder 456200.
The pick-up shoe is installed under this locomotive. It is wired so 236 406-5 is the
front end of the double locomotive.
In 236 405-7 a 35 gram weight is installed where the reversing unit used to be.
Later I swapped the decoder from the 60901 set with a 60922 mfx decoder, from a 60924 conversion set.
The 60901 decoder in 236 406-5:
How the smaller mfx decoder looks in a V36, this is 28502:
The weight in 236 405-7
The weight is made of self sticking balancing weight for car wheels, 10+5+10
grams in one "row", 10 grams glued to those. A 2,5mm hole was drilled for
the screw.
Finally it was painted black.
Lamps:
The original lamp holders in the locomotives are still used, now with 600100
bulbs and a 180 Ohm serial resistor,
to cope with the higher voltage from the decoder. The resistor wire end is
used as threads for the bulb. See the two above photos from the motor side.
The original bulbs, 600190, was only rated for 1,9 Volts.
I have covered the light guides to the rear lamps of both locomotives so
only the front lamps are working. Next is to cut two rubber tubes to put
around the bulbs to prevent unwanted light distribution.
The interior lights are 28 Volt T1 bulbs, glued to the motor magnets. White paper ceilings are installed in
the driver's cabins for better distribution of the interior light.
The wiring diagram:
The decoder connections:
| Wire colour | function | Connecting to |
|---|---|---|
| Red | B (center contacts) | pick-up shoe connector |
| Brown | 0 (tracks) | locomotive ground, preferably to both locomotives |
| Blue | Motor brush | left brush holder in 236 406-5 and to the right holder in 236 405-7. See photos. |
| Green | Motor brush | right brush holder in 236 406-5 and to the left holder in 236 405-7. See photos. |
| Orange | Common + | bulbs, two in each locomotive (front lamps and interior light) |
| Grey | Forward lights (f0-f) | serial resistor on the lamp holder in 236 406-5 (front lamps front locomotive) |
| Yellow | Reverse light (f0-r) | serial resistor on the lamp holder in 236 405-7 (front lamps rear locomotive) |
| Brown/red | function 1 (f1) | interior light in 236 406-5 |
| Brown/green | function 2 (f2) | interior light in 236 405-7 |
My setting of the mfx decoder:
| Decoder settings, 3346 | Default | Mine | |
|---|---|---|---|
| Analog settings: | |||
| Enable analog mode | check | < | |
| Starting voltage | 7,300 | < | |
| Maximum voltage | 23,000 | < | |
| Control settings : | |||
| Swap directions | uncheck | < | |
| Max. speed | 255 | 84 | |
| Min. speed | 4,000 | < | |
| Acc. time | 7,000 | 10,000 | |
| Dec. time | 3,750 | 10,000 | |
| 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 | < | |
| Control parameter K | 60 | < | |
| Control parameter I | 120 | < | |
| Control influence | 255 | < | |
| Special options: | |||
| Preserve direction | check | < | |
| Persistent acceleration | uncheck | < | |
| Persistent speed | check | < | |
| Persistent functions | check | < | |
The mfx decoder functions:
| 3346 DB DB 236 405-7 and 236 406-5 | |||||||
|---|---|---|---|---|---|---|---|
| mfx | Light | Light driver | Shunt speed |
Acc/ dec |
|||
| function | direction | front | rear | front | rear | ||
| f0 | forward | 3 | |||||
| reverse | 3 | ||||||
| f1 | both | on | |||||
| f2 | both | on | |||||
| f3 | both | on | |||||
| f4 | both | delay off | |||||
| f5 | both | 3 | 3 | Shunting mode f0-f + f0-r + f4 + f5 |
on | delay off | |
Screenshot from my Märklin Central Station 1:
The left part is the 28502, the right part is the double DB 236.
The bottom right brake delay icon is removed.