This post may be a little premature, as I have not taken the loco apart since I noticed the problem....
but I have three identical lightly used Atla/kato C-424s that I put NCE D13SR decoders in. One loco slowes down aconsiderably fter running and warming up, while the others do not...so much so that it cannot be speed matched at the moment.
My first thinking is dirt....wheels, commutator etc, etc.
But they all seem in identical condition. Anyone have an issue like this thay they can tell me to be on the lookout for when I start dismantling and cleaning this one of a triplet?
Thanks
Check your decoder and make sure you haven't inadvertently reset the Max Voltage (CV 05) to something other than 255 or 0.