I have a brace of Kato SD40s in Algoma Central colours that of course I always run together (which is not only prototypical, but necessary to haul a heavy train up my 2% grades). Both are equipped with Digitrax DN163K1C decoders, which is a drop-in replacement for the factory light board. Then one day, one of the locos stopped running. The lights worked, but not the motor. After a little experimentation, I determined that it worked fine running solo, but the minute I consisted it (using Advanced mode), it became no more than a pretty decoration. Very strange, but electronics sometimes fails in weird ways.

I happened to have a spare DN163K1C on hand, so I replaced the decoder, and got the loco working again. Great -- but now I had this sort-of-working decoder lying around....and an Ontario Northland SD75I I was dying to see in action. Guess what decoder the Digitrax website recommends for the Athearn SD75? Yep: DN163K1C.

Turns out it's not quite a drop-in job, though. While the decoder board fits mechanically in the top of the Athearn frame, unlike in the Kato units, the motor doesn't have the contact tabs on the side that engage the tabs on the decoder. This motor just has a couple of whiskers coming out the end -- I had to disassamble the frame before I found them, they're so small. But I was sure that, with a bit of ingenuity, I could get my decoder installed on this unit.

First, I soldered 30-gauge wires on the little motor whiskers. Which of course I forgot to take a picture of until I'd reassembled the frame:

I drilled holes in the decoder tabs, and soldered the other ends of the wires through them (note the generous application of Kapton tape to insulate the tabs from the frame):

Perform a factory reset on the decoder, reprogram it, and here is ONR 2105 switching the transfer terminal. I'm feeling quite pleased with myself!