Bizarre Shortcircuit

[Sails]

I'm running in a Heljan 128 today, the van gets half way round and then I get the short circuit flashing up on my Lenz controller. Reset try again and shorts out in exact same place. Reset, reverse then on a different corner its shorts out. Put on programming track to check for short circuit and nothing.
Really weird it happens in exact same spot, other locos running just fine. I'm not electrical wizard but suspecting it might be the 128's internal wiring for lighting s there is a lot, but that would account for the regularity of shorting in the same location.

Any thoughts?

Mark

[Bufferstop]

The clue may be in the description "reverse then on a different corner its shorts out." My guess would be that part of the wiring is being moved by the rotation of one of the bogies and causing a short circuit. DCC power supplies have a very sensitive detector for short circuits so by the time you can get to the wiring to examine it the short circuit may well have gone away. If the wiring is at all untidy or loose try to tuck it out of the way, but look out for wires being twisted together especially close to their terminations. I'm not familiar with the layout of the 128 but some intermittent faults on other models have been caused by the back of the DCC socket touching parts of the chassis. Happy hunting

[Bigmet]

Unlikely to be the lighting circuits, because then what you would see are one or more lights not working on the loco (and quite possibly decoder damage unless it has overload protection). That's not something the DCC system will detect as a short circuit, as the lighting outputs are on the DC side of the decoder. If the lights all work as they should, then no worries there.

You are looking at the track power side when the DCC system detects a short circuit and shuts down. Because it is happening on curved sections it is possible that one of wires that make the pick up connections between the wipers and the board has detached and the free end is waving around as the bogie moves, occasionally contacting where it shouldn't: and there's a short circuit on the track power side. Another possibility is a metal 'foreign object' lodged in a bogie, less likely but needs to be checked for if you cannot see a detached wire.

I have a 128, and I don't think there is any need to check the back of the decoder socket as this is a 21 pin unit, and sits above clear space in the chassis casting; so the once common problem of contact on the back of the 8 pin socket seen on some Heljan models shouldn't happen on this one. It is such a simple internal layout that i am a little stuck for what other troubles there might be. But report back with what you find and if the problem isn't solved more 'thinking cap on' will be attempted.

[Sails]

Thanks guys, will continue the detective work later this evening.

Edit,

I should be able to narrow down which bogie to concentrate on easily enough, last night I put the loco on my Gaugemaster wheel cleaning brushes, it shorted then, so I'll repeat move the bogie around and then identify the bogie. Guess that means I wont be painted the doors and frames again tonight!!

[Sails]

Problem Solved, luckily it wasn't anything too technical in the end. When I finally had a chance to get back to this a good inspection of the bogies found that two pickups had been bent through almost 180 degrees (one on each bogie). I unscrewed the cab insides from the chassis and was able to get a thin tweezer down to (almost) straighten the pickups.

[Bufferstop]

What's the odds of one bent on each bogie?