Installing a DCC decoder in a Frateschi DC locomotive

Introduction

I got a Frateschi model train as a christmas gift last year. The locomotive only supports DC, so a decoder installation will be more complex compared to DCC ready locomotives. The locomotive is a GM G-22CU for the railway company KiwiRail. Product page for the locomotive from IronHorse Hobbies can be found here.

Tools

I used the following tools for the decoder installation.

Please note that I used a smaler plier than what is shown in the above list. The tip activator is only needed if the solder doesn't stick to your soldering iron.

Inside the locomotive

The locomotive shell can easly be detached from the frame by gently pulling the sides outwards. The circuit board and and wiring inside this particular model is extremly simple. Bellow is a picture of what the inside looks like.

This is the first time I have installed a DCC decoder in a DC locomotive. I therefor did some reseach about the topic before proceeding with the installation. I found this video from Soundtraxx to be quite useful. One of the steps they talk about in the video is about isolating the motor. That is needed for locomotive where one of the track wires is directly connected to the motor, which is not the case with this model as the track pickups are connected via the circuit board.

Installing the decoder

I initialy purchased an ESU Loksound 5 decoder with a MTC21 connector together with a MTC21 socket. Bellow is a picture of the decoder and socket.

That decoder install worked for one day before it stopped working. The installation looked like this after I was finished installing it for the first time.

Initialy wireing where done according to the bellow table, which was based on the decoder wireing diagram in the included manual.

Socket terminal	Function	Locomotive wire
8	Front light	Left side of the circuit board
9	Speaker output	Speaker
10	Speaker output	Speaker
16	Lights common	Right side of the circuit board
18	Motor	Upper motor terminal
19	Motor	Lower motor terminal
21	LHS pickup	Left hand side pickups from the bogies
22	RHS pickup	Right hand side pickups from the bogies

So what happened? The first run where sucessfull. Lights was working after i flipped one of the diodes and sound was ok. Bellow are two pictures from the first runs.

The locomotive was still working at the start of the next day, but then I suddenly noticed that the overload protection of my Z21 command station kicked in. I first thoughht it was my T-class that caused the issue as I was doing some tests with that locomotive at the time, but that was not the case at all. I then started suspecting the G-22CU, which was a correct suspicion. The shell of the locomotive was quite hot. I then opened up the shell to find a decoder that was so hot that I barely could touch it.

I therefor decided to test the decoder with my recently acquired decoder tester from ESU. Plugging in the decoder in the tester showed that the decoder was acting wired. The adress that I was able to read out from the decoder was wrong, it made funny noises and it was not possilbe to reset it.

Then an idea came to mind. I still had the broken Soundtraxx decoder from my T-class laying around. It had some wires connected to it from last time I tried to troubleshoot it, so I therefor decided to plug it into the decoder tester. The wired thing is that I where able to factory reset and program the decoder using the tester. I therfor decided to attempt installing it in the locomotive.

I started by removing the components from the failed installation. I then had to remove the circuit board due to the design of the Soundtraxx decoder.

I then had to solder on the wires for the pickups and the motor. Bellow is a picture of the result.

I initialy tried to solder on the ESU speakers. I placed those under the axels, but those speakers simply wouldn't output any sound. The speakers where glued into place using superglue. I have later removed them as they didn't work with the Soundtraxx decoder.

The same story goes for the lights. I wired them to the decoder output for LEDs. I then reprogrammed the decoder to use that output. I also tried to change the polarity of the output through programming and I also tried to reverse the polarity of one of the diodes. They simply wouldn't turn on no matter what I did. I also did a diode test to verify if they would light up then, which they did. I suspect that the decoder outputs for lights and sound simply doesn't work. Bellow is a picture of what the installation looked like after installing the diodes and removing the speakers.

The good thing though is that the motor works fine with the decoder, which at least allows me to operate the locomotive.

Final thoughts

This locomotive has so far fried one decoder. That is the second decoder destroyed this year! Lets hope no further decoders wil be destroyed. I have some thoughts about why the decoder got destroyed.

One theory is that I simply added too many components in to little space. The strange thing is that the decoder burnt out while standing completly still without any functions enabled. So that could also be a indication of a short circuit.

Another theory is that some other component heated up the decoder, thus resulting in its destruction. One reason why I suspect this is that I have noticed the motor becoming quite warm during operation using the Soundtraxx decoder. That heat could potentialy transfer up to the circuit board and then travel further up to the decoder. One factor that could disregard that theory is that the socket bellow the decoder wasn't hot. Heat travels upwards, so the socket should probably have been quite warm too if that was the case.

But those are just theories. I have no way of knowing for sure what caused the incident. One thing is for sure though. I won't attempt the decoder installation this way the next time, as it will likey have the same result.

What about the current issues like no sound and no lights? Well, I will keep the locomotive as is for the time being, as I am able to drive it using the broken Soundtraxx decoder. I might replace that decoder later, but I will have to observe for some time to see if the Soundtraxx decoder will work well over time. There is no point in installing a new decoder if it will just end up broken. Its clear to me now that installing a DCC decoder in this particular locomotive requires more thought than initialy predicted.