Updated 15.06.2009

Märklin 3346, DB 236 405-7 and 406-5

Conversion parts:
For the 3346, which requires 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.

Later I swapped the decoder from the 60901 set with a 60922 mfx decoder, from a 60924 conversion set.  New photos will follow later.

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.

The 60901 decoder in 236 406-5:

How the mfx decoder looks in a V36, this is 28502:

The weight in 236 405-7

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, firstly without the brushes. Check once more that everything revolves effortless. Install the brushes.

The motor in 236 406-5:

The motor in 236 405-7:

Lamps:
The original lamps in the locomotives are still used, now with a 180 Ohm serial resistor, to cope with the higher voltage from the decoder. See the above photos.
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 light are 28 Volt T1 bulbs. White paper ceilings are installed in the driver's cabins for better distribution of the interior light.

The wiring diagram:

The decoder number in the diagram is for a c91 decoder.  The mfx decoder is 60922 and has the same wiring.

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 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 decoder functions:

mfx 60922		Light		Light driver f.	Light driver r.	Shunting speed	Acc/ dec	Shunting speed	Acc/ dec
		front	rear
f0	f.	3
	r.		3
f1	f.			on
	r.			on
f2	f.				on
	r.				on
f3	f.					on
	r.					on
f4	f.						delay off
	r.						delay off
f5	f.	3	3					on
	r.	3	3					on
f6	f.	3	3						delay off
	r.	3	3						delay off