Just released (got the email 5 minutes ago) is Railpro's new module the LM-3S-21 (
https://www.ringengineering.com/LM-3S-21.htm). This is welcome news
I have been testing the beta/prototype version for a few weeks now and can report my experiences. I tested the new modules on a new Rapido GP38 and a ScaleTrains Dash 9. Both were DCC-ready models. The module itself is a little shorter than the LM-3S and about the same width. One end has the 21-pin connection. The final dimensions on the production module will be slightly smaller (not as long and not as thick) than the beta modules.
Installation on the Rapido was quick and straightforward. I simply removed the factory 21-pin placeholder and plugged in the LM-3S-21. That was it. It fit perfectly in the spot and did not bind on the shell at all once it was reinstalled. It took quite literally 2 minutes to remove the couplers and shell, install Railpro, and put everything back together.
This is the Rapido model as it comes from the factory:
Here is the Railpro module installed:
Just enough space under the shell, no interference:
The LM-3S-21 works perfectly on the Rapido model. All lighting functions work, the factory keep alive capacitors work, and Rapido was even kind enough to include speakers already installed. The model runs great and the Railpro module is just as you would expect. Functions are largely the same as the LM-3S with exception of all the extra lighting functions and outputs.
I also installed one in a ScaleTrains DCC-ready Dash 9. Installation took a little more work, partly because of ScaleTrains design problems and partly because the case on the beta module was too big. Retail versions will have a smaller case to prevent the problems I found. The ST board from the factory:
The factory wiring for the motor prevents seating of the 21-pin module.
I had to reroute and solder the wires in a different configuration.
The front edge of the module was prevented from seating by the DIP switch on the ST board. Production LM-3S-21 modules will have a cutout here to prevent this problem.
Installed:
Now, it became apparent that ScaleTrains made some design choices with their boards that are really unfortunate. They designed them so that only their ESU 21-pin decoder can access all the functions (lighting and keep alive) on the board. It's a known problem with other decoders, and it's no different with the Railpro LM-3S-21. There are ways around the lighting function bottleneck, but it involves soldering a bunch of resistors in specific locations on the ST board, and is neither approved nor thoroughly tested. Those hacks don't unlock the built in keep-alive capacitors either. So the 21-pin Railpro module does indeed control 4 lighting functions and can be used on the ST board, but like all other decoders it cannot do anything more. It's a truly awful choice by ScaleTrains to design their locomotives this way. In my opinion, the best way to install Railpro into a ST locomotive is to remove the stock board and throw it in the trash where it belongs. Then install a LM-3S and PBM-2. There is just enough space in the stock board location for both of those.
Overall I've very pleased with the LM-3S-21 and am excited to see it available. This will make installation and use with newer models easy (except for ScaleTrains) and enjoyable. It's really nice being able to access all the lighting functions now. I've tested it with the HC-2, HC-3, and CI-1/HC-Sim combo....everything works as expected. The LM-3S-21 consists well with the LM-3S and LM-2S, and has had no problems running well with various locomotive manufacturers.
-Kevin
