Heyside: 7mm L&Y, late 50s/early 60s
Richard,
I think JB's got it. I've had similar problems with some of my HO stuff and I'm pretty sure it's a command interrupt on the main bus. Therefore a set of snubbers (terminations to the bus) would help solve the problem. I'd recommend wiring in series a 1w 150Ohm resistor and 0.1microfarad capacitor of suitable voltage (24v should do it). These are then connected across the ends of the bus. They'll stop signals being reflected back along the bus so reduce the amount of noise/traffic and so provide a clearer set of commands to the decoder. These aren't always necessary, but with the sort of problems you're describing they're a damned good, cheap start to a solution.
Twisted pair is a good idea for the buses, a much better idea than using screened cable even. Ferrite rings near the command station can also help; but we're getting into overkill here. In an exhibition environment we took some care to make sure that our power supplies were well protected (ferrites, seperate fusing, etc) as some DCC systems aren't well contained and can squirt considerable amounts of noise back on to the mains. Mind you, this is all good practise on analogue layouts anyway!
I'm less worried about dodgy pickup these days. 18v AC can jump most of the dirt we're likely to have, to keep the decoders powered. Capacitive coupling across any dirt seems to be a 'feature' of most modern decoders: hence Lenz and their USP technology allows you to command a loco even when there's a layer of paper between the track and wheels! Iron oxide on steel track is more of a problem as it's actually a very good insulator, on nickel-silver you should be okay though.
I'll be happy to see how your decoders are set up. I am not a fan of the Lenz decoders with coreless motors as the manual doesn't help you set up the drive. I agree that what you're describing is probably the feedback over-driving the motor. The Lenz decoder's drive can be tailored; I just can't find out how! I use Zimo or (better) ESU decoders with my coreless-motored locos, the new ESU LokPilotv4 looks like being a stunning piece of kit, although I've not used one yet (you can use an on-board PSU with it).
The Lenz and Power1 combination is one I use in smaller, conventionally-motored, tank locos with great success.
BTW - you have set your locos for digital-only operation in CV29 haven't you? It seriously impacts the quality of the running of all decoders and will allow the Power1 to actually do something, rather than just being a bit of extra weight to carry around!
I'll send you a PM with my contact details so you can drop me the JMRI files when you're ready.
Steph