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Short cuts to finding a short.....


gordon s

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Just finished wiring a stand alone board, DCC with 5 Tortoise motors, three turnouts and a switched crossing and I have a short. I generally check as I go along, but with the finish line in sight and tiredness creeping in, I missed that vital step.....:angry:

 

I spent an hour or so looking at it yesterday but can't see whats wrong. Because of the size and curvature of the board, I can only lay it flat and see one side of the board at a time which is a nuisance with a problem such as this, but that's the way it is I'm afraid.

 

Having now visually checked both sides and all appears OK, I am at a loss what to do next other than disconnect the wiring. Before I go down that route is there any way you can tell with a meter if it is electrical via the wiring or mechanical via the track? One of the downsides of DCC and multiple feeds is that there seems so many feed options that disconnecting one at a time will not show a short as a secondary feed can come via the rails or another dropper.

 

Any got any bright ideas, just before I go and desolder 100+ wires?

 

No doubt I will look at it now and it will be staring me in the face and before you ask, there are no tools or locos sitting on the track......;)

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My forst question is:-

Is any of your track built on copperclad sleepers. If so one way I used was to clip the meter to the rails, prop it so that you can see the display, then go round every piece of copperclad with either a file or a cutting wheel on a Dremel or something similar. At some point a little whisker of copper will come free and the short will clear. This can all be done on the top of the board.

 

If you don't have any copperclad the only thing that I can suggest is that you divide the layout into a few logical section and disconnect the necessary droppers, then test each section in turn. Then you cna arrow it down. As you go you can connect long leads to the droppers to each section, connected to you meter, then again work on the top with the meter display visible to you.

 

Hope this is of some use.

 

Jamie.

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if you have a very fine multimeter you can sometimes tell where the short is approximately from the resistance readings, it will be higher the further away from the short you are.

 

I had a short on Fourgig at the Mansfield Show that turned out to be the interlaced sleepers at the heel end of the point, the multimeter told me it was at that end even though it's only 4ft long.

 

Good luck :unsure:

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Hi Gordon.

 

The first place I would look at is the droppers.Are they connected to the correct bus wires ?

The second place would be the points & crossing.Have you fitted all the insulated joiners where needed or are there gaps cut where they should be?

The 3rd place to look is the frogs.Have you connected a frog wire to the wrong bus wire ?

 

If you are working in an area where its hard to see a meter,then make up a buzzer with a 9volt battery & a little 6 volt buzzer & a couple of pieces of wire. That way all you have to do is touch two areas & if you have a connection the buzzer will sound with no need to look at any meter.

Hope this is of some help to you.

 

EDIT: If you've ballasted the track ? Is the ballast dry ?

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Yes I do have copper clad pointwork but each turnout is checked before ballasting in position. I also use copper clad sleepers to feed power to the track and have checked all those. All OK so far.

 

Tried the resistance test Ian, but I suspect my Wavetek meter is not sensitive enough. The whole layout is reading 00.6 ohms +/- 00.1 ohms irrespective of the position on the board.

 

I guess the only thing now is to cut through the track and divide into sections. and then it's back to a few hours of deduction and brain work. I have no idea how some guys do it under exhibition conditions......

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As the track was tested before installing I would put that to the bottom of the list.

I also would not unsolder anything at the track end, the most likely problem will be connecting a wire to the wrong terminal. Possibly swapping a frog lead with a dropper.

 

Check Rule 1 - every frog MUST be isolated (I hate the short cut wiring where just because a frog goes to a siding or following point this step is missed out/fudged) - every point should be independently wired - It has 3 droppers, one for each stock rail and one for the frog. I try to take these to a local choc-block connector so that every point can be isolated.

 

Is there any part of the track that works?

 

Are all the wires colour coded?

 

Check all the frogs leads from the Tortoises. Set all the Tortoise to mid point throw (are the points bonded rail?)

 

If anything, it will be another of those salutary experiences - test test test as you go along.

When you find the fault it will suddenly be a obvious mistake and why didn't I think of that moment.

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I use both John, but all pointwork is checked before installation. I learned that one the hard way with track pins. No shorts off the board but as soon as they were pinned down the short returned. Seemd to take weeks to find that one.....Dope!

 

I've disconnected all the frogs and all are OK but short stil there. Just in the process of checking all the droppers now....

 

I'll get you, you little blighter. Tiredness and poor eyesight are the main problem....:D

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I use both John, but all pointwork is checked before installation. I learned that one the hard way with track pins. No shorts off the board but as soon as they were pinned down the short returned. Seemd to take weeks to find that one.....Dope!

 

I've disconnected all the frogs and all are OK but short stil there. Just in the process of checking all the droppers now....

 

I'll get you, you little blighter. Tiredness and poor eyesight are the main problem....:D

 

Here's an idea to assist in preventing such a nasty from occuring next time.

 

Grab yourself a buzzer and battery & connect the two ends to the two rails, now as you connect the wiring together & if you accidently create a short the buzzer will suddenly start buzzing. The fault will probably be the last wire you connect.

 

But BE AWARE that if you use a multimeter with this feature, it may go to sleep automatically after a delay, giving a you an utterly false sense of security.

 

:help:

 

 

Kevin Martin

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Found it! Hooked up a buzzer and then disconnector each dropper. One of the bad habits I have got into is twisting 2-4 wires together before soldering to the bus. I realise now that disconnecting the bunch of wires does not disconnect them from each other, so it makes sense to solder the wires to the bus one at a time and not all together.

 

Thanks for all your inputs guys. Seems I have been doing the right thing and there is no magic answer by analysing results via a meter that would point me in the right direction. Apologies Redgate, there is one but my meter is not sufficiently sensitive to indicate the lower resistance.

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<Snip>

Check Rule 1 - every frog MUST be isolated (I hate the short cut wiring where just because a frog goes to a siding or following point this step is missed out/fudged) <Snip>

I couldn't agree more. ;) ;)

To many layouts and 'wiring experts' allow frog feeds to go out into sidings or onto other points etc. This often leads to future problems, especially if the track plan is altered beyond these point(s) at some stage later on.

The rule of thumb I use and recommend to all layout builders is 'Fit IRJs (two) onto the ends of each elecrofrog point Vee rails'.

The fitting of insulated rail joiners or even gapping of the rails leading away from electorfrog points frog is correct for both the dc and DCC user.

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I have just read the post where you found it, so well done and the high when you fix it is mind blowing innit.

 

I was going to suggest a slight bodger's approach. Go to the layout at midnight on a night with no moon and drawn curtains, stick you head underneath and switch on. You will see the spark. Aim a torch at it........

 

Oh yes I did!!!

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I have just read the post where you found it, so well done and the high when you fix it is mind blowing innit.

 

I was going to suggest a slight bodger's approach. Go to the layout at midnight on a night with no moon and drawn curtains, stick you head underneath and switch on. You will see the spark. Aim a torch at it........

 

Oh yes I did!!!

 

:yes:

 

A similar variation on the theme is to turn the wellie up and see where the smoke rises from. B)

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:yes:

 

A similar variation on the theme is to turn the wellie up and see where the smoke rises from. B)

 

That only works on DC and a coarse thermal cut out. I, and the OP, are DCC. Instant cut out.

 

I had to switch on several times before I spotted the spark at a far reach of the layout and then several more times to get it torched so I could see what was causing it.

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As the track was tested before installing I would put that to the bottom of the list.

 

Not with copperclad, it's very easy for a whisker of metal to cause a short after the track has been laid and ballasted - ask me how I know :angry:

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Making provision to isolate bits and testing as you go seem like a lot of effort for nothing until you get a short. And doing it upside under a layout with an exhibition due to start just adds to the fun.

Don

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