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Your Layout and Models => Track, Points and Underlay => Topic started by: Papyrus on May 15, 2019, 07:35:31 PM

Title: Faulty plain track?
Post by: Papyrus on May 15, 2019, 07:35:31 PM
Here is something very strange.

I've finally laid my last pieces of track (Peco code 80) and have been running a loco round to check it is all OK. There is one section of track which appears to be dead. I've cleaned the rails and checked the usual suspects - track joiners, point blades etc - nothing looks amiss. So I got my circuit tester out and found a good electrical connection through several pieces of track including 3 points, but as I ran one probe up a piece of plain track the connection suddenly disappeared. I hadn't moved it past a track connector or any other type of break in the rail that I could see. The only explanation I can come up with is a hairline break in the rail but that seems very unlikely to me. Has anybody else had something like this, or can anybody come up with an explanation? The obvious remedy is probably to simply replace that section of track, which I will probably end up doing, but I'd still like the mystery solved.

Cheers,

Chris
Title: Re: Faulty plain track?
Post by: ntpntpntp on May 15, 2019, 07:52:53 PM
Seems very odd to lose conductivity half way along a continuous piece of rail. It would have to be broken right through to fail like that, which should be obvious. 

Photo of the spot where the break occurs?
Title: Re: Faulty plain track?
Post by: Ditape on May 15, 2019, 07:53:00 PM
Interesting snag, I have not come across this before, I look forward to seeing what the problem is and how you solve it. ???
Title: Re: Faulty plain track?
Post by: bob lawrence on May 15, 2019, 08:04:37 PM
How about running a dropper from each side of the suspect split to the buss?
Title: Re: Faulty plain track?
Post by: stevewalker on May 15, 2019, 08:11:33 PM
Isn't it likely to be some non-conductive contamination. Try cleaning it thoroughly?
Title: Re: Faulty plain track?
Post by: Newportnobby on May 15, 2019, 09:33:02 PM
Sounds like a job for Muldur & Scully to me :uneasy:
Title: Re: Faulty plain track?
Post by: Papyrus on May 15, 2019, 10:07:28 PM
Photo of the spot where the break occurs?

This is where the 'break' is. Sorry the photo is upside down but it didn't seem worth turning it.
(https://www.ngaugeforum.co.uk/SMFN/gallery/77/2975-150519214255.jpeg)

Close-up. You can just see a very slight imperfection on the top of the rail - a slight indentation you can feel with a probe.
(https://www.ngaugeforum.co.uk/SMFN/gallery/77/2975-150519214353.jpeg)

Isn't it likely to be some non-conductive contamination. Try cleaning it thoroughly?

Yup, did that - cleaned the whole rail with IPA.

As mentioned above, I've replaced the rail and it now works fine. I put the circuit tester across the rail now that it is off the layout and it detects no fault. The only explanation I can come up with is that there is a poorly-conducting imperfection which allows electricity to pass when the probes are close to the 'break' but if the probes/power supply are further away the voltage drop is enough for the imperfection to cause a blockage.

As an aside, I lied when I said I had laid my last piece of track.  :( I'm going to have to re-lay another section of the layout, but that's for another thread...

Cheers,

Chris
Title: Re: Faulty plain track?
Post by: themadhippy on May 16, 2019, 12:15:51 AM
For finding these sort of faults you really need a low impedance voltmeter, a 100 ohm resistor across the test probes will do the trick.
Title: Re: Faulty plain track?
Post by: Bealman on May 16, 2019, 01:04:30 AM
I guess that's wot you get for telling fibs  ;D ;)
Title: Re: Faulty plain track?
Post by: MJKERR on May 16, 2019, 07:27:25 AM
Is this piece of track already embedded in to the layout, or has it been removed?

Simply remove the faulty piece of track and replace it with a fresh piece
If the fresh piece exhibits the same fault, then the wiring is at fault
If the fresh piece resolves the issue, then the track is at fault, and simply dispose of it

Equally, is the layout DC or DCC?
What is the spacing of the supply droppers?
How long is the piece of track?
For my DCC layout the droppers are spaced at intervals of 60cm, this does mean some pieces of flexitrack have two sets of supply droppers but ensures that there is a power supply in the event one dropper fails
Title: Re: Faulty plain track?
Post by: Bealman on May 16, 2019, 07:32:49 AM
It has been replaced (post #6)
Title: Re: Faulty plain track?
Post by: Dr Al on May 16, 2019, 01:18:46 PM
Looks dirty on the RHS as compared the left, so I'd clean properly, with an abrasive block (e.g. Peco track rubber). IPA wll take off dirt, but not sure it will deal with oxidation.

Cheers,
Alan