Note: The first part of this documentation dates from 18.08.2020 and was updated on 04.09.2023 with the chapter “Addition of SUSI-Sound.”

The housing of the locomotive is held in place by four screws accessible from below (under the bogies).

Since replacing the 21mtc decoder with a CTC-Lokmodul-21mtc is a breeze, I’ll start here with the IR receiver.

The IR receiver finds its place next to the bogie without the slider: In this locomotive, the bogie has enough play so that I don’t need to drill a hole in the housing for the cables of the IR receiver:

Then, the 21mtc decoder is replaced by the CTC-Lokmodul-PluX22 and the IR receiver is plugged into it.

Initial test runs show that the locomotive has either no buffer or a buffer that is far too small. Since the locomotive’s board (as is unfortunately typical with Märklin) is undocumented, I refrain from looking for a connection for the buffer capacitor there. So, a capacitor with 1000 uF is soldered to the solder pads provided for it on the CTC-Lokmodul-21mtc:

This is what the fully converted locomotive looks like. If I had not wanted to install the IR receiver, it would have been enough to remove the roof to replace the decoder with the CTC-Lokmodul-21mtc:

Addition of SUSI-Sound

The BR247 was equipped with a 21mtc sound decoder from the factory. We replaced this with a CTC-Lokmodul-21mtc, thus initially losing the sound. As of the firmware 20230902 delivered with CTC-App 4.19, the CTC-Lokmodul-21mtc can be supplemented with a SUSI socket.

The following image shows the locomotive extended with SUSI-Sound. An Uhlenbrock IntelliSound 6 (32600) was used as the sound module. The sound module was packed in heat shrink tubing and is positioned at the top left next to the CTC-Lokmodul-21mtc. The factory-installed speaker could be reused:

The corresponding schematic looks like this, see also the manual Chapter 9.1 - “Sound with SUSI Interface”:

The following image shows the wiring in more detail:

• The two black cables on the right side of the 21mtc connector are connected to the speaker output of the SUSI sound module.
• The two cables on the left side of the 21mtc connector are the power supply for the SUSI sound module (red=VBB=SUSI_Plus, black=GND=SUSI_Ground). VBB and GND are also found on the other side of the CTC-Lokmodul-21mtc as larger solder pads. But since the buffer capacitor was already connected there, it seemed easier to use the contacts of the 21mtc connector.
• The 10-pin mini connector, which so far was only connected to the IR receiver, is augmented by two connections: The purple (blue) cable connects “Input-1 (Pin 33)” on the CTC-Lokmodul-21mtc to the “Clock” pin on the SUSI. The gray cable connects “Input-2 (Pin32)” on the CTC-Lokmodul-21mtc to the “Data” pin on the SUSI.
• The white socket at the bottom left is the SMD socket designated for SUSI classic, to which the cables could also be conveniently soldered directly.

In addition to the new firmware, a new “ioCfg.xml” is also required, which has been extended by the SUSI-connection (Port). With CTC-App 4.19, there is a new button “Replace IO-Config” in the configuration, which can be used to accomplish this, see Chapter 4 - “Configuring Modules”

To reprogram the sound module, the SUSI connector is unplugged from the SUSI classic socket connected to the CTC-Lokmodul-21mtc and plugged into the Uhlenbrock IntelliSound loading adapter: