Uploaded March 2022 | Updated September 2026, 2 weeks ago
The Museum Quality HO Scale SDL39 diesel locomotive has numerous lighting features that utilize all outputs on a 21MTC interface decoder.
In 2020, the NMRA updated the standards for 21-pin (21MTC interface) DCC decoders so up to 12 function outputs can be used. We recently learned most US-focused DCC manufacturers have not updated their decoders to this latest NMRA S9.1.1.2 standard which means all 12 function outputs are not available on their decoders. When a non-ESU decoder is installed in an SDL39, the lighting functions will likely not work.
To compensate for other DCC manufacturers not adopting these new standards, we’ve developed a workaround for customers who prefer to utilize other brands of DCC decoders. Basically, a small wire bridge needs to be installed on the SDL39 main board to enable the AUX9 output, pin 5 on the 21MTC interface (AUX12 on ESU decoders). This output is connected to Pin 16 (V+) on the interface to turn on the internal voltage regulator.
Note: ScaleTrains is not responsible if the mainboard and/or DCC decoder are damaged while completing this solution.
If you are not comfortable soldering the jumper wire onto the mainboard, you’re welcome to ship your SDL39 to our service department.
ScaleTrains.com, Inc.
Attn: SDL39 Jumper Wire
7598 Highway 411
Benton, TN 37307
We will install the jumper wire for $20 including return shipping. We will email an invoice for payment prior to performing work.
Learn more about the SDL39 here: bit.ly/ScaleTrainsHOSDL39
The Museum Quality HO Scale SDL39 diesel locomotive has numerous lighting features that utilize all outputs on a 21MTC interface decoder.
In 2020, the NMRA updated the standards for 21-pin (21MTC interface) DCC decoders so up to 12 function outputs can be used. We recently learned most US-focused DCC manufacturers have not updated their decoders to this latest NMRA S9.1.1.2 standard which means all 12 function outputs are not available on their decoders. When a non-ESU decoder is installed in an SDL39, the lighting functions will likely not work.
To compensate for other DCC manufacturers not adopting these new standards, we’ve developed a workaround for customers who prefer to utilize other brands of DCC decoders. Basically, a small wire bridge needs to be installed on the SDL39 main board to enable the AUX9 output, pin 5 on the 21MTC interface (AUX12 on ESU decoders). This output is connected to Pin 16 (V+) on the interface to turn on the internal voltage regulator.
Note: ScaleTrains is not responsible if the mainboard and/or DCC decoder are damaged while completing this solution.
If you are not comfortable soldering the jumper wire onto the mainboard, you’re welcome to ship your SDL39 to our service department.
ScaleTrains.com, Inc.
Attn: SDL39 Jumper Wire
7598 Highway 411
Benton, TN 37307
We will install the jumper wire for $20 including return shipping. We will email an invoice for payment prior to performing work.
Learn more about the SDL39 here: bit.ly/ScaleTrainsHOSDL39
