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Quick query about cable testers

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Quick query about cable testers

Postby nathanscribe » Sat Apr 21, 2018 3:25 pm

I've got no experience of cable testers, I usually just use a multimeter to check continuity. But I've noticed while monitoring signals on my oscilloscope that it's possible to have a cable that passes a signal, shows continuity just fine, but clearly has some fault because the signal is degraded through it (specifically here I was looking at a low audio rate 5V pulse, which showed up through this cable as 3.75V, and only a severe waggling would momentarily fix it).

It's easy enough to snip the jack off and re-solder it, but do generic audio cable testers show this kind of fault, or are they simply testing for continuity?

Hope this makes sense.
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Re: Quick query about cable testers

Postby Hugh Robjohns » Sat Apr 21, 2018 5:14 pm

Most only test for continuity with a lowish Dc voltage applied between the nominal ground terminal and each signal pin in turn. Some also have an 'intermittent mode' where they apply the volts on all lines simultaneously so you can flex the cable and look for drop-outs.

A few advanced signal gen/cable testers send audio signals at low and high frequencies and look at the return levels to try and identify damage causing major capacitance anomalies, but they are rare and not really worth the expense.

A simple DC cable tester followed by a quick listen is good enough for me.

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Re: Quick query about cable testers

Postby ef37a » Sat Apr 21, 2018 5:57 pm

I was once asked to build a tester for intermittent O/C cables and CAT 5x jacks.

All 8 wires were looped in series and then a button pushed which latched a miniature relay. Even the briefest open would cause it to drop out and light a LED.

For 'our' purposes find a DMM with a 'squeaker' on the Ohms range and croc solidly to cable and wiggle. You will soon hear the tone drop out and even change timbre if there is a change of resistance.

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Re: Quick query about cable testers

Postby resistorman » Sat Apr 21, 2018 8:37 pm

The Behringer CT200 tester is very good. Even the CT100 goes beyond most testers.
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Re: Quick query about cable testers

Postby nathanscribe » Mon Apr 23, 2018 8:23 pm

Thanks chaps! Question answered deftly. :thumbup:
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