Curious fault

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Steve M
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Curious fault

#1

Post by Steve M » Wed Apr 01, 2020 6:11 pm

This one has me scratching my head.

I have one of the new Hornby Dean singles fitted with a bog standard Hatton’s decoder and its a good performing, easily controlled loco.
However, last week the front bogie derailed causing a short. Immediately afterwards it’s direction of travel had reversed and it seemed to have only two speeds, dead crawl or flat out. That wasn’t a DC runaway as it was still controllable, well up to a point anyway.

I reset the decoder and all seemed good - until today.

The loco stopped on a point, it didn’t derail but I suspect another momentary short occurred. Once again, little control and reversed direction of travel.

I know a short can cause spike which can disrupt decoders but I’ve not noticed these symptoms when I have derailed or shorted other locos.

Any thoughts on why this one is particularly sensitive?
I’m not a complete idiot, some pieces are missing. ;)

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Brian
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Re: Curious fault

#2

Post by Brian » Thu Apr 02, 2020 11:42 am

Hi Steve
Short circuits, even turning on and off a DCC system and occasionally when placing a loco onto live DCC feed rails can all cause micro second spikes to appear on the rails / DCC bus pair.
Any 'receptive decoder' and these are frequently budget range decoders will at times reset, though many "Upmarket" decoders will weather the spike and carry on as normal.
If you add bus filters to the DCC bus they will help overcome this problem.
Each filter in nothing more than a 2 or 3 watt 100R to 150R resistor in series with a 0.1uF ceramic capacitor with a minimum 50volt working wired across the bus pair. Components needed are shown here https://www.brian-lambert.co.uk/DCC_Pag ... Bookmark16
Image << Click the Icon to go to my website

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Steve M
Posts: 1572
Joined: Thu Oct 04, 2018 5:29 pm
Location: Rochester, Kent
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Re: Curious fault

#3

Post by Steve M » Thu Apr 02, 2020 12:31 pm

Thanks Brian, I already have bus filters which is why I’m surprised it’s happening. It’s not a problem with my other locos/decoders (I tend to only use budget decoders) so possibly just this one is sensitive.
I’ll swap it out when I get a chance and see if anything changes.
I’m not a complete idiot, some pieces are missing. ;)

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