Cable Tester

[Kaiowas]

Does anyony knows a good cable tester schematics or project? (hopefully XLR and 1/4")

Thanks!

[yano]

Would It be possible just plug the two ends of the cable into jacks that had probes for your multimeter? Then just measure the resistance through each line in the cable and see if it within specifications?

[Tubebass]

Look here:
http://www.fortunecity.com/tinpan/humperdinck/223/ctester.jpg
   Regards,
   Tubebass

[Ed G.]

Check out the Rolls Cable Detective, there is a schematic in the PDF:
http://www.zzounds.com/media/ct1man-de2cac1d945986ab7dff98dca26451ca.pdf

I like it because it not only tests for continuity, it also detects shorts, which can still maintain continuity. I built one without the MIDI jacks, just for mono/stereo 1/4" and XLR.

[Paul Perry (Frostwave)]

When the inner wire of a shielded wire breaks, you can tell which end it breaks at (it is nearly always the end!) by measuring the capacitor fiormed by the inner conductor and the shiled, at each end.
It is worth making a jig to connect to your multimeter's cap inputs.

[Primus]

My brand new fluke 27 doesn't have capacitance leads. Is there a way to modify one of these cable test circuits to have an additional green LED that only lights if the capacitance of the cable is acceptably low? Preferably the one that detects shorts. Perhaps you could dial in what is acceptable w/ a variable resistor. Anyway, this would help a lot of people w/o fancy multimeters.

[KerryF]

Cant you just buy a Continuity Tester (sp?).  It has a metal clip on one side and a metal pointer thing on the other.  Poke around with each to see whats connected to what.

[Primus]

I did some searching and read a bit and this is what I came up with. I think it is essentially a consensus, but please please correct me if I am in error. There are X properties that you want to be able to test in a cable:

1. Continuity
         For this, you can just use a power source and an LED.

2. Shorts
         For this, you can try to power an LED off of the ground lead of the cable. The LED should not light. This is part of the circuits mentioned above.

3. Resistance
         This should be essentially 0, and if the cable has any continuity at all you can expect it to have 0 resistance no matter if it is a patch or a 20 ft cable. You can test this with a meter if you care to, but it's not important for a cable tester.

4. Capacitance
         This can be a problem because it will attentuate highs if it is higher than about 200 pF to 470 pF. By 1 µF it is quite noticable. It'd be nice to know if your cable has high capacitance and if you don't have a meter that can do it it'd be nice to have a circuit that could tell you when calibrated with standards (ie, off the shelf capacitors with known values).

[rockhorst]

I'm working on a scaled down version of the Cable Detective now, supporting XLR and 1/4" jacks. Hope to finish it tomorrow.

[grapefruit]

I use a Behringer CT100 cable tester all the time. It's rip off of some other brand - they may not be in business anymore. For around $70 Australian I wouldn't bother making my own. It tells you if there's continuity, shorts, intermittent continutity - for XLR, Jack, RCA, and MIDI. It also has built in oscillator, and lets you know if phantom power is available. It's sure saved me a few times for on site service work.

FWIW I'd rather use the original but this unit was provided by my employer and cost about 1/3 the price.

Cheers,
Stew.

[rockhorst]

Building your own would cost you under $15, incl. aluminum case...That's still quite a nice difference from $70...

[moosapotamus]

Craig Anderton's "Tri-Test" Cord Checker is pretty nice (I built two of them). It's in Do-It-Yourself Projects for Guitarists. In addition to checking for both shorts and continuity, it also checks for intermittent failures that a simple LED circuit would miss - i.e. the "crackly" cord that still passes a signal. Designed to only check unbalanced cables. Would be nice to mod it to check balanced XLR, too.

~ Charlie