In the thread about 3071 in the H0-forum I promised to report about the conversion of my 3071 (and 4071).
First I opened the control car (the rear coach if the engine is pulling the train). The control car also has a slider, which is in use if the train is pushed in stead of pulled. The red lights are always on, as expected. If the control car is in front, the yellow lights overpower the red ones so you hardly see them.

I had decided to add a resistor to protect the rear light from the higher digital voltage; I found a 12 Ohm resistor and soldered in between the rear light and the slider. The resistance of the rear light appears to be some 45-50 Ohms, so the 12 Ohms should be OK to limit the voltage over the lamp to 16. The other red wire goes to the motorcar to feed the engine if the control car is in front; the yellow wire is for the headlight of the control car..

The dimming effect of the resistor is not as high as I wanted, so maybe I'll add another.

Then came the more interesting part. First opening the motorcar:


The analog controller of direction, lights and sliders is complicated:




The decoder (a 66032 from M*) is connected; I fixed it to the chassis with Velcro.




Ofcourse the leads from the decoder have to be shortenend. I will do this after I receive the later mentioned bi-stabile relay I have on order at Conrad. This relay was ment for switching the power in to the slider in front of the train, depending direction of travel.

Then it was time for a test run. I made the mistake to connect the controlcar at first ride. Apparently I put the connector upside down, because when I switched the power on, the decoder made a loud buzz and a little cloud of smoke. The decoder output for the front light at the controlcar must have gotten connected to the slider of the control car, which is on the digital power from the track (the other lead through the train was not yet connected).
Then I tried the loc on itself, and then the loose connector touched ground, gave a small spark and that was it. [:I][:(!][xx(]

But after all the only damage is to the switching of the lights function. Lights still work, but are always on (both sides). Rest of the decoder works fine. At the time the train is running with yellow lights in the motorcar and red lights in the control car. Running it the other way is possible, but leads to derailments.

So my plan is now to add a bi-stabile relay, connected to the motor-controls (green and blue wire from the decoder) to switch headlight from front to rear. Maybe I'll also connect the red rear lights accordingly. The power for these lights will be direct from slider, not from the decoder. I think it will also be possible to effectuate changing from one slider to the other this way.



Evaluating this conversion I think it is not a good idea to use the leads through the train for power which comes from the decoder. To put the train together, you have to connect three connectors between the coaches and - as appeared - it is easy to connect them the wrong way. In analog service this is no problem, the only thing that will happen is probably that the rear headlight and slider won't work but in digital operation it is fatal for the decoder.

Hope this helpes those of you who are planning the same conversion.

Regards, Henk.

It is 66032 Delta decoder from M*. It is hard to see in the text above one of the pics. I had this one available and I find it very useful for these older M* engines.
Regards, Henk.

Very nice, Henk.

To avoid derailment when running "backwards", I have added some weight to the end of the control car. I have not tested on M-track, but it works very well on C-track.

Last week I received the double switching bi-stable relay from Conrad to finish the conversion. Everything is as expected now; lights switch red and yellow for back and front; front slider is used for power pick-up; I only have the original 2 wires through the train. And what's important, I think it doesn't matter anymore if the wires through the train are switched accidentally: in stead of frying the decoder the unit just will keep sitting were it is.
I exchanged the 12 Ohms resistor in line with the rear light of the steering-car with an 33 Ohms resistor (this light is always on, if the headlights of the steering car are on it is overpowered). The lights now have the right strenght.

Switching the relay through the green and blue wires from the decoder did not work. So I had to go back to my original plan and exchanged the partly fried decoder (lights are always on, without changing by direction) with another decoder from a loc where changing lights do not matter but which is still full functional. So the signal of the front/rear lights (grey and yellow) from the decoder are used to switch the relay. I connected the relay as follows:

connection 1: grey wire from decoder (forward light signal)
connection 2: yellow wire from decoder (backwars light signal)
connection 3: is connected via a 12 Ohm resistor to connection 8 (power input from sliders)
connection 4: output to headlights of steering car (yellow wire through the train) and rear lights of motorcar (black wire)
connection 5: output to headlights of motorcar(yellow wire)
connection 6: input from slider of motorcar (black wire)
connection 7: input from slider of steering car (red wire through the train)
(when I made the picture, the connections 6 and 7 were the wrong way around)
connection 8: output of relay from either front or rear slider; connected to red wire (input) of decoder and via a 12 Ohm resistor to lights (connection 3)
connections 9 and 10: ground (of engine, not of decoder)
The decoder is a M* 66032 Delta decoder; the relay is from Conrad, made by Takamisawa; part # 503398-8A; works from 9 - 22 V DC and can swith 35 W/60 VA at max 250 V AC/220 V DC; so that gives some extra.
In the end it looked like this; it is hard to see how the connections are made but it works! Good luck for whoever wants to follow this conversion too. In the end it's really easy.
Lesson learned is never to connect an output of a decoder to leads which are not connected permanently and thus can be connected wrong.
BTW the derailment problems are also over, had probably to do with bad connecting the cars to eachother.
Regards, Henk

Edited by moderator 11 January 2011 19:45:33(UTC)  | Reason: Not specified

Henk: Thanks for this.--MM