Ok, small contribution from me. Sorry my layout doesn't have any scenery like many of the fine contributions above, but here's what I was working on the other day. A couple summers ago at a show, I picked up an older Atlas Master series Dash 8-40BW. The seller insisted it was new old stock, but on closer inspection at home, the already programmed loco address and one missing sunshade made me think perhaps otherwise. It also ran a little funny-- the motor worked fine, but the grade performance puzzled me. Going up or down grade (my layout ruling grade is 3%), it would either dramatically slow down or speed up respectively, with a constant throttle setting. That behavior was the same if running light, or pulling cars. I expect some performance effects going up or down hills, but this loco did it to almost comical effect compared with my other equipment.
The locomotive came with (what I think was) Atlas' early "analog DCC" which I suspected was the cause. It didn't come with a manual and I didn't feel like tracking one down to see how easy it would be to reprogram, so I ordered a new non-sound DCC board from Soundtraxx. I also replaced the bulbs with LEDs, and was going to also put small LEDs behind the ditch lights, when I ran out of patience. Getting the shell off/on, breaking one brake cylinder while trying to reattach the brake chain, etc. just led me to call it a day. I've discovered on these DCC installs, I'm really good at carefully measuring out how much wire to use, figuring out where to put the resistor, soldering it in place, adding liquid electric tape, and then finding something I did won't work. In this case, I discovered I couldn't reinstall the cab floor because the resistor I put beneath it was just a shade too thick.
Anyway, long story short, I eventually got it all back together and it runs great now--no performance issues on grades anymore. I may try and install the ditch lights in the future someday, if I feel brave enough to try opening it up again. Here it is back in service with a Fox Valley GP60M (with which it consists very nicely, probably because that also has a Soundtraxx decoder in it too):
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