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Installing A Märklin Sound Decoder In A Class 234 From Trix

A model train

Märklin has two special kits for adding sound to Trix (and Märklin) locomotives of the families ER20 (Hercules), TRAXX and classes 232 and 234 (Ludmilla). I thought I would try out a kit as I have a few of the class 232, 234 and because it would be a fun little project.

The Märklin Sound Decoder is called "mSD". This is a fully updateable locomotive decoder for use in all locomotives with a 21 pin MTC plug. You can also buy the decoder as an 8-pin version. Using the Central Station 2 (CS2) (Märklin #60215, #60214 or #60213), you are able to update the sound in the mSD. You can also use the Märklin Sound-Programmer (Märklin #60801) and update the decoder using your PC. If you do not have a CS2 or Sound-Programmer, your dealer can help you update the sound.

Installing The Decoder

For this project I used:

  • A model of a class 234 (Trix #22069)
  • A Märklin Sound Decoder "mSD" (Märklin #60948)

First you need to take the locomotive apart and get an overview of what is about to happen. The instruction book that comes with the decoder is very easy to understand and you should read it from start to finish before going ahead.

A model train
The Trix version of the class 234 comes with an 8-pin decoder plug. Unfortunately this is not enough for the kit, so we need to install the motherboard anyway.

The mSD kits includes a loudspeaker that will fit in the locomotive's loudspeaker compartment, the decoder itself and a new motherboard for the locomotive. The motherboard is included because the locomotives normally do not have a 21-pin decoder plug.

Info: In this particular locomotive (Trix #22069) the motherboard actually has an 8-pin decoder plug. I could have choosen to install an 8-pin version of the decoder. I did not choose this, because I wanted to try out the kit with the new motherboard. The price is the same, so you do not pay extra for the motherboard.

The Motor

First unplug the flexible bircuit boards that holds the lighting boards. Make sure they are not in the way when you use your soldering iron.

A model train
The light strips are easily unplugged from the motherboard.

Now unscrew the motherboard by removing the four screws in each corner. You can use the small compartments in the decoder's packaging for storing the screws and small parts from the locomotive while you install the new decoder.

A model train
You can use the decoder's packaging as temporary storage for small screws and other stuff.

Carefully detach the wires that are soldered onto the motherboard. Depending on your model there might be three or four of them. You can now lift the motor and motherboard away from the locomotive's frame.

Warning: Working with the motherboard can be a bit tricky because the motor is soldered directly on to the motherboard.

You must be very careful when separating the motor and motherboard. When the motor is removed from the old motherboard, the motor must be soldered onto the new motherboard. Again, take care when doing this.

A model train
Lifting the motherboard out of the locomotive. The motor is soldered onto the motherboard.

A model train
The motor is now free of the old motherboard.

Because I had some problems when removing the motor from the old motherboard, I gave it a couple of test runs using an analogue controller and a switched mode power pack.

A model train
A simple test run of the motor.

Luckily, the motor was fine. Now the time has come to install it onto the new motherboard.

A model train
Test fitting the motor on the new motherboard. The white wires are for the loud speaker. They come pre-soldered onto the motherboard.

When putting the motor back into the locomotive, remember to attach the cardan axles to the motor before putting it back. This makes things a lot easier for you. It is impossible to install the cardan axles after the motor is back in the frame.

When everything is in place, attach the four screws and solder the wires back onto the motherboard.

A model train
Attach the cardan axles and put the motor back into the locomotive.

The Loudspeaker

The mSD comes with a loudspeaker that will fit into the locomotive's loudspeaker compartment. The installation is easy, simply pull the white wires through a hole in the locomotive frame (the hole is already there, you do not need to make it yourself) and solder the wires to the loudspeaker.

A model train
The white wires are soldered onto the loudspeaker. You can do no wrong here, it does not matter which of the wires that goes where.

To keep the loudspeaker in place, use the loudspeaker lock that comes with the decoder. You simply push it in place and you're done.

A model train
The loudspeaker lock makes sure that the loudspeaker cannot fall out during operations.

That's it! Assemble the locomotive and put it on the track.


You can use the locomotive as is. It already has a diesel sound (although not the right one) and the decoder is preconfigured for the motor in this particular range of locomotives. Although that can be fun, I want that very distinctive sound of a Russian diesel engine. That is why a bit more configuration is necessary. ;-)

The mSD supports both the DCC and mfx formats. For the fun of it I thought I would try the mfx format for this locomotive. I have a few other locomotives that uses mfx and the format have impressed me. Mostly because I find it extremely easy to configure the decoder. You can use whatever format you prefer.

The decoder comes preconfigured with a sound of a diesel locomotive (ER20, Hercules). Since this is no way near the sound of the class 234, of course, we need to replace the ER20-sound with the sound of a class 234. Unfortunately there is no sound available for the class 234, but there is one for the class 232. The two classes are almost identical, so no harm done, we will use the class 232 sound instead.

I put the locomotive on the track and my CS2 immediatly recognized the new locomotive. The small mfx logos on the screen tells you that a new locomotive is available. Click either of them and begin the configuration process.

A model train
The Central Station has recognized a new mfx locomotive.

Update The Sound Scheme

To update the sound click the "Upd" button on the locomotive configuration screen. This will take you to the decoder update screen. There are several sections of the decoder that can be updated simultaneously. The one we need is the "Sound Flash" section. 

Click the little folder button and locate the file you downloaded from the website. If you only have the sound file on your USB-stick the Central Station will automatically suggest that one.

Tip: You can check the other folders to see if the Central Station has found any newer versions in the update file. If that is the case, select them as well and update the other sections along with the sound section.

A model trainThe sound update screen.  

When you are ready, click the button with the little locomotive and the arrow to update the decoder.

Note: The locomotive needs to be on the programming track while updating the decoder firmware and sound.

Have patience! Depending on the decoder and the size of the sound project the process can take a very long time.

When the update is done, you can go ahead and do some additional configuring.

Configuring The Decoder

The first thing I do when setting up a new locomotive is to give it a name. I use the number of the locomotive. Since this is 234 292-1 this will be the name of the locomotive. The mfx decoder allows you to type in owner information, I do that as well. I consider it a nice little touch. :-)

The decoder comes preconfigured with some settings. I always test the default settings first and then make adjustments until everything is to my liking.

Since this is a mfx locomotive we do not need to set the address nor the decoder type. If you were to use DCC, you would have been able to set an address as well.

A model train
The Central Station locomotive configuration screen.

The next thing I do is to adjust the sound volume ("Lautstärke" in the screenshot). Sound decoders often come with a very loud setting and I really cannot stand that. I think a locomotive should make just enough noise for you to hear it from a distance of 1 meter (approx. 3.2 feet). I found that a volume of 180 was suitable for this locomotive.

The maximum speed ("VMax") is set to 110. This is purely a personal preference. I like my trains to run quietly and smoothly around the layout and not speeding like a slot car. To prevent guests from turning my layout into a slot car track, I limit the maximum speed.

Speed Curve
I like to be able to have some control of locomtives when they are moving at slow speeds. I found that changing the speed curve to (in CS2 terms) "Progressiv" gives me what I want. A "Progressiv" speed curve is close to a logaritmic curve.

A model train
Setting the speed curve to "Progressiv" gives me better control of the locomotive.

The last thing I do is to sort out which functions I need on the locomotive. I usually have the light on function F0 and some of the standard functions on F4 and F5. Everything else - in the case of this locomotive - is reserved for sound functions. There are more sound functions available in the decoder than the CS2 can make use of, but several of the sound functions double as "random operating sounds", meaning, that they will fire from time to time anyway. I removed those sounds from the function list.

I then reconfigured the shunting mode to also turn on the double A light in both ends of the locomotive (shunting warning light). This is a nice little touch that I will enjoy whenever I use the shunting mode.

A model train
The "double A" light will turn on whenever you activate shunting mode.

This was a very long post and I hope you have read along so far and I really hope you enjoyed it! If you want to try out an easy to configure sound decoder, you should try out the Märklin Sound Decoder "mSD". Look for a version that will fit your needs.

Besides the two kits for the classes mentioned above, they have several other kits available depending on what type of locomotive you have. Both for 21 pin MTC and 8-pin NEM plugs.


Here's a video of the decoder and loco in action.

As you can see, it turned out pretty well!

Happy modelling!