I have a beautiful Märklin Crocodile 3352 Ce 6/8III SBB in Brown color from 1987.

This Loco is the first Crocodile with metal body after the 3015.
The frame is similar to the previews models with the plastic body and actually the same period the Green Crocodile 3356 had a plastic body.
Later the 3556 came with metal body. Is exactly the same with the 3352 in green color and 5 star motor.

The 3352 has a DCM 3-pole motor, relays with electronic circuit reverse unit, and Swiss light change (only white, no red).



The conversion planned as follows
1. 60941 5 pole motor
2. mLD/3 decoder with 4 AUX functions
3. LED lights
a. Front-rear white-red Swiss changeover
b. Cabin lights
4. No sound

This is not an easy conversion. Is quite tricky.
The conversion take about five months to complete.

The problems are:
1. The very limited space in the Loco
2. The light changeover

I gave solutions to all the problems and the conversion is a great success.
We will discuss the problems and the solutions in time.

The same conversion apply exactly to 3556 and other models with the same frame (3056, 3652, etc) with small differences mainly on the light holder, but there are many possibilities for the lights.

I hope that this will be interesting.

Thanks
Best regards
Costas

Next step is the very well cleaning of the trucks, motor housing, gears....



Close inspection (and inspection of HD photos) .....



No problems detected



You can notice the small bronze soldering plug on the front track, this is used as another ground (brown) connection.
This is necessary because the frame is articulated. In later models has been replaced with a screw and a plug.
I left it as it was and I haven't any problems.
But you can do 2M threads and put a screw.







Everything OK time for the next step: Motor replacement

Costas

The Swiss light changeover with only white lights is easy and can be done with a small circuit with 4 diodes, and does not need any function except the f0 for the light changeover.

The red taillight on the other hand is a problem.
There are solutions from Märklin in different Swiss Locomotives that are different depending on the time and the Loco.

There are many solutions but the main difference is if you will use 1 or 2 functions to control the red taillight.

The solutions with one function are more complicated and in the limited space of this Loco you must use PCB with to many SMD components ( 5 transistors plus diodes, resistors....).

Märklin used a solution like this in 3956x Crocodiles with part no 606218. This part is no longer available and in newer Locos they use simpler solutions.

On the other hand the 2 functions solution is easier.

As far I had two AUX functions available I decide to follow the easier for me solution.

So the functions will be

f0 (f0-front: white, f0-rear: yellow): the light changeover with control of the white taillight

AUX 1 (green): Control of the red taillight in the rear part of the Loco
AUX 2 (violet): Control of the red taillight in the front part of the Loco

AUX 3 (violet/yellow): Front cabin light
AUX 4 (violet/white) : Rear cabin light

The circuit plan of the Loco is this one (NEM color code):



The parts used:



The white LEDs are actually Golden White. The resistor values can be different according to the LEDs that will be used.

I checked it on the breadboard with success:

Front direction white taillight



Front direction red taillight



Rear direction white taillight



Rear direction red taillight



So after the theory we have to do it.....

First I decide to use 1.8mm LEDs on the sockets of the original bulbs, with small modifications and use the light transferring lenses as they were.

So you can see the result:

Front of the panel with the three LEDS



Rear of the panel (I used the original plugs for the LEDs (4 of them) plus one small hole from where I pass the common (+) of the white and red LED)



The panel in place



Do it 2 times one for each side of the Loco.

Some remarks:

In the diagram you can notice that I put the drooping resistors on the (+) of the LED's (blue wire) and not on the (-) as I do normally. That has not any effect and in this case the PCB is simpler this way...

I have stop using protective diodes for a long time, and so far I never had a problem.
The use of diodes is may be useful with decoders without protection of the final stages.
Of course that make the whole circuit simpler....

I have leave now and I will be come back tomorrow with the PCB and the cabin lights


Costas

Edited by user 06 March 2017 23:45:53(UTC)  | Reason: Not specified

Great work Costas, congratulations!

In my conversions, I have used the standard 622550 diode boards for SBB light changes, but your board is more convenient, including the resistors.

I'm still puzzled by your circuit plan:
as far as I see, you always have 3 white leds on with F0(f) or F0(r).
How would you switch on 2 front leds and one red at the rear, while leaving the rear white led off?
Is this due to the voltage difference between the white and red led?

[img]Costas
I have a Hamo 8356 loco that I want to convert to digital. My current setup is an the 3 rail analogue M track system.
I have read numerous Marklin forum discussions on this subject (digital conversion) and am keen to attempt it.
My question is whether the Hamo 8356 is similar to your 3352 conversion?
Attached pics with body removed.
Thanks
Benders