A small upgrade for the Minitrix Köf II, one of the smallest N scale engines.

Bad engine, bad!

Minitrix had released several digital versions of the cute little Köf II shunting locomotive. There were also DC versions as well.

I have 2 models, old and new Deutsche Bahn livery:

Minitrix 12544 and 12288 - Köf II

Minitrix 12544 & 12288 Köf II

Minitrix managed to build a very small engine, and even included front and rear headlights. As expected at this size and weight, this locomotive can easily get stuck without power.

But it turned out the (Doehler & Hass built) factory decoder wasn’t really top notch. The engine wasn’t really behaving well, even on clean straight tracks, and I wasn’t the only one complaining.

DH06A decoder as a replacement

The same company who built the original decoder for Minitrix, Doehler & Haass, has since then released a new decoder. The DH06A has been specifically designed for the Minitrix Köf II, its shape, and its 6V micro-motor. It even includes 2 LEDs to light up the driver cabin as a bonus.

The DH06A can be bought where other Doehler & Haass decoders are available. But the brand also offers an exchange program. If you send them back the original decoder: the DH06A will cost you 18€. The exchange program page is here (in German, use google translate if needed).
The topic has been discussed a lot on german forums. Yes, it seems unfair for a company to basically cash twice (once from Minitrix, and then a second time from the user buying the DH06A decoder). On the other hand, Minitrix (Märklin) may have given D&H very little money or a poor requirements list originally.

Doehler & Haass DH06A decoder for Minitrix Köf II

Doehler & Haass DH06A decoder

Doehler & Haass DH06A decoder for Minitrix Köf II

Doehler & Haass DH06A decoder (side view)

In any case, the DH06A has been praised as a big improvement on the original decoder. The Minitrix Köf II uses a small 6V motor, so other decoders cannot be used (at least not without additional DIYing).


Changing the decoder requires precise soldering and isn’t really for beginners.
I personally added additional capacitors (4x100uF) to even further improve the engine’s driving characteristics. Those have to be soldered directly on the components (cables visible in picture below). They can be placed in the driver cabin, where there is a little room for SMD components.

Minitrix 12288 - Köf II and original decoder

Original decoder

Minitrix 12288 - Köf II and DH06A decoder

DH06A decoder soldered

Minitrix 12544 - Köf II and DH06A decoder

DH06A decoder tests

Minitrix 12544 - Köf II DH06A decoder with buffer connections

DH06A in place with extra wires for buffer capacitors



Both Köf II engines with the DH06A decoder now behaves way better than before. Don’t expect miracles though: it is still a very small and light locomotive with 4 wheels. It may still get stuck occasionally, but way less than with the factory decoder. This was all tested even before I added the 400uF buffer.
So if you know how to solder and have one of those little engines, a decoder update may be in order.

Special thanks to Christian from http://www.modellbahn-diepholz.de who motivated this modification and explained how to connect the capacitors. He also has a much nicer Youtube video than mine, that you can see here.

External links