I have a Proto2000 HO-scale SW9 equipped with the NCE SW9-SR decoder, and it “jumps” ~1 inch whenever power is first applied to it. If this only happened when I energize the track, I could live with that; but it does the same thing if it rolls over a spot where input voltage may be a bit weak (such as an insulated-frog turnout). And sometimes it jumps in the opposite direction from where it’s supposed to be moving. Seems as if something is dropping a full-strength jolt across the motor leads! Needless to say, this is a major annoyance during switching operations and coupling/uncoupling.
Does anybody have a clue why the decoder would make it behave this way, and what might be done to correct it (other than installing a new decoder)?
I don’t have an answer but I have found that having an RRampmeter connected to my layout generally gives me a better idea of what is happening. For example, If the current draw is increasing when the loco jumps, generally means a short or bind in the mechanism.
The only time I’ve seen a loco change direction on it’s own was when running a DCC loco in DC mode. Every time it hit an insulated frog, it reversed.
OK, I disabled it by setting CV29=034. That appeared to solve the problem - for about 1 minute, until the loco stopped responding to any commands at all… [%-)]
(Wiring was OK)
I followed the reset instructions in the NCE manual, by setting CV30=002. This did indeed reset the CVs - but not to factory defaults, it changed every one of them to 255!
I think I must have fried the decoder at some point…[xx(]