Speakon failure

[paulears]

Time Domain reflectometers - mentioned by Brian are used by BT (and others of course - the railway companies being another typical user). Cables have electrical properties - resistance, capacitance etc - and as once you know the cable spec, then you can use careful and accurate measurement to tell you how far the open or short circuit is from the test point. The clever test gizmo fires a short pulse down the circuit, and looks for the tiny reflection. It can use this to produce results that a skilled person can interpret. The scope trace will show time (and thus distance) plus if any capacitive elements are present. People who work daily with cable faults are very good at reading the results. As an aside, they're also pretty good at showing why DMX lines shouldn't be passively split, and why a terminator is a good move!

 

The only snag in your case is that even if you know there is an open circuit 22m down the line - if you don't know where the cable actually is, it doesn't help very much!

[Alec]

As well as an expensive TDR, you can also use a Cable tracer (I just gave the first link that Google found, no need to use Maplin, and they're available from many places.

 

One end injects a signal into a cable, and then you can use a probe to listen to the signal further along the cable, without contact. Makes it a doddle to work out which is which in a bundle of cables, and would help identify if yours had simply been miswired. And can, if there's a fault, go someway to identifying roughly where it is - i.e., which is the last working bit of cable.

[Brian]

It can use this to produce results that a skilled person can interpret.

The one sitting in my test equipment drawer goes as far as having an LCD display which gives a direct readout in metres to the open circuit.

[timsabre]

It can use this to produce results that a skilled person can interpret.

The one sitting in my test equipment drawer goes as far as having an LCD display which gives a direct readout in metres to the open circuit.

 

Can you rely on the number given though? I used to use them on the railway quite a lot and they were very dependent on the sample of cable used to teach it the characteristics of the cable. Spent many hours hacking through undergrowth to faults that turned out to be 100s of metres away.

[dbuckley]

Having a TDR with a scope view can tell you a load about the general state of the cabling one is dealing with. If there are myriad impedence discontinuities then one can guess there is trouble ahead.

 

However, for the prelim the OP has, one a meter has determined the nature f the problem, a tone warbler might be enough to find the problem.

 

Sounds a quite strange problem though...

[Owain]

An alternative approach is to measure the capacitance from each end. The ratio is the ratio of distance to the fault. Assuming the cable is the same type throughout, this will work on unknown cable types.

 

You don't need a capacitance meter eithe

 

http://electronicsproject.org/de-sauty-bridge/

 

 

[S&L]

slightly different context and just by way of anecdote..I once spent several hours in a control panel, wiring in a new controller and couldn't work out why it why outboard controls wouldn't work from it.

eventually it dawned on me... the original installer had wired it backwards - positive was negative, negative was positive. I reversed the wiring (effectively wiring it the wrong way round) and it operated correctly. just because it isn't upside down now, doesn't mean it wasn't upside down before!

[dan slv-tech]

worth checking also that circuits they re wired havent been crossed over with others? easy to label things but so much easier to wire them back on the wrong socket. esp if your terminating left to right from one side of the panel but labelled it left to right on the other side :

 

Id stick a speaker on the end of the lines, and with 9v battery and check every line

id lay penny to a pound its there somewhere, be it mis wired, or wrongly labelled.

 

Unless youve had some buildings work done, I cant see how a cable would stop working.

 

silly question, but the source your using to drive the speaker line is working? correctly? connected correctly? and same goes for the load on the end of the line?

 

D

[john-sp]

I have on two separate occasions found older speakon NL4s that have suddenly stopped working. After spending quite a long while checking for cabling faults I eventually found that the NL4 panel socket itself had failed, with no continuity from the front of the socket to the rear. No idea why and it took ages to come to that conclusion as I wasn't expecting that to be the fault. I replaced the socket and the system worked fine. As I said these were both installations that had been around for about 10 years in different areas. It might be worth checking continuity through the sockets if that could be the problem.

 

 

 

John

[Alec]

Unless youve had some buildings work done, I cant see how a cable would stop working.

 

As was said earlier - rats!

[Oldradiohand]

Unless youve had some buildings work done, I cant see how a cable would stop working.

 

As was said earlier - rats!

 

Rats and mice are very good at eating insulation which will result in shorts and (if the voltage is high enough) death of the rodent involved. Can't see a rat eating through the conductor of a speaker cable, though.

[Tregilibob]

On the rats.....

The building in on the 3rd floor, concrete floors, and the speaker cables are encased in metal box trunking where they are not inside a wall....... Never seen any rodents, or heard any, or seen the aftermath of any......

Both speakers work, both sets of cables work (first thing I checked!)

Have checked wiring to make sure its the same, checked the speakons continuity, still got to get to the only point I can't get at, but that is on its way.

If I get no success from that, going to get the tester out to see where abouts the signal stops, and see if that helps.

 

Thank you

[Tregilibob]

So far, after buying a cable tracer, I can confirm a) I may have concussion from the stupid roof space I've just been through twice, and b) I get a signal on both cables, all the way to the end, albit the black is a weaker signal (LED doesn't light up as much).

After lunch (and trying to not fall asleep) I will check out the other pair that don't give me a speaker signal out, and see what happens with that. Hopefully a better result without a trip to A and E!

[Tregilibob]

Add- just tested the 2nd speakon connection, red (positive) full signal with tester, black, again slightly less.

I've just re-tested the speakon connectors, and signal front to back is perfect (using multimeter) and thought "I'll just test the speaker again"

There is some sound, very low, distorted, but only with mixer and amp fully up.

 

Any more ideas from the wonderful blue room?

[MarkPAman]

OK, this is quite a long thread now, so I may have missed it, but have you proved that the amp and speakers work properly when not using this cable?

 

If you short out pins 1+ & 1- at one end of the cable, what resistance (or impedance if you've got a fancy meter) do you measure at the other end? Then take the shorting connection out and measure again.