This is a real mystery, this one.... I have a Weaver O Scale Geep, 2-rail, Pittman motor, shaft drive via delrin chain on a tower to rear axle, then shaft drive to all axles. A few years ago I fitted a 'boosted' Soundtraxx Tsunami 3amp dcc decoder to it, and all was well and good until last year, when the loco started behaving strangely - when the speed was set, at anything above speed step 1, the loco would get to that speed, and utterly ignore any further commands, like slowing down, stopping, etc. It just kept going regardless. I thought maybe the decoder was at fault - I've found Tsunami's to be fussy things, liable to stutter at random, on clean track that other decoder-equipped locos go through no problem. So I've replaced the decoder with an ESU Loksound L, again 3amp rated.... and the same 'runaway' problem is occuring. While "in between" decoders I wired it for DC and tried it on analogue - no problems at all. I've checked the wiring and pickups for any sign of breaks or shorts - all looks ok, and it doesn't trip the system anyway, which is NCE Powercab with NCE 5 amp booster. Cleaned the wheels, including the rear faces that the pickups contact. Then I've tried it with a similar motor (Pittman). Same runaway issue, so it isn't a motor fault, BUT - here's what's really mystifying - with the drive shaft disconnected, i.e. no load on the motor, it behaves itself ok. Starts, stops, reverses, all according to throttle settings. Re-connect the drive shaft, and it misbehaves again. The fact it's done it with two different decoders, that were both new, and have even had CV8 reset by me just in case, leads me to say it's not a faulty decoder either, but clearly something is happening when the motor is under load that is scrambling the decoder signals. The drive train does not bind or catch, there's some slack in it, and with everything connected up it all turns easy enough by hand. I'm utterly at my wit's end with this issue. Anyone come across anything like it before??? Or any ideas what might be happening?? Photos show the loco innards, minus speaker, excuse the slight rats nest of wiring, also shows the driveline (disconnected from the motor).