Short in XLR shield ?

A

andrew gissing

Sophomore
Jan 11, 2011
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Perth Western Australia
www.stylusra.com.au
I've got a weird one.

I made some cables for a guy 5+ years ago; they are all individual (ie not a multicore) and run about 10m from his studio vocal booth to an equipment rack. Individual canare star quad cables; box in booth; line plugs other end; and cable just lays on the floor tracking around the walls of the room.

I was called this week because one of the cables is now buzzing. I go have a look and find that pin 1 from end-end does not make a circuit; 2 & 3 are fine.

So I open up the box with chassis plug, and unscrew the line plug (both Neutrik); expecting to see that one end has shield loose on pin 1.

Nope; both plugs good for all three pins. I also test from the exposed bit of cable/solder to the other side of the plug and that works too.

The shield looks good and solidly connected to the shield still wrapped under the outer rubber.

and I did test the patch cables I used to join up both ends and they both worked.

I wasn't able to get the cable out to take home because it's cable tied with a few others - I made a new one to fix the problem. I did look over the length of the cable and nothing stood out as outside damage.

But I'm at a loss to understand how the cable could have a short in a braided shield ? A drain wire with foil I could conceive a situation where that may happen. But not braided.

Has anyone come across anything similar or have ideas on what could cause this ?

I'm kinda looking forward to the guy getting the cable loose for me and i'll start chopping it up to find out where the break is.


Andrew
 
Re: Short in XLR shield ?

To be clear, that's an open, not a short..

And yes it does seem odd. a braided shield doesn't just come apart mid cable without some serious damage.
I'd suspect a cold solder joint, or maybe if the solder at the end wicked too far and made it outside the connector strain relief then repeated bending could cause a break.
Before going to too much trouble I would cut a few inches off and re-terminate

Jason
 
Re: Short in XLR shield ?

Jason Lavoie said:
To be clear, that's an open, not a short..

And yes it does seem odd. a braided shield doesn't just come apart mid cable without some serious damage.
I'd suspect a cold solder joint, or maybe if the solder at the end wicked too far and made it outside the connector strain relief then repeated bending could cause a break.
Before going to too much trouble I would cut a few inches off and re-terminate

Jason
Click to expand...
Yes, there is a big different between a short and an open. But many people think that anything not "correct" is a short. WRONG

I have seen brand new cables that have breaks in them along the length. I am talking not cables with ends-but rather cable off of a brand new spool. I have seen "thins spots" that break the first time you flex the cable etc.

You don't want it to happen-but it does.
 
Re: Short in XLR shield ?

Ivan Beaver said:
I have seen brand new cables that have breaks in them along the length. I am talking not cables with ends-but rather cable off of a brand new spool. I have seen "thins spots" that break the first time you flex the cable etc.

You don't want it to happen-but it does.
Click to expand...

He did mention Canare star quad though, and it is in a studio, not dragged behind a truck, so I'd go out on a limb and bank on the shield being intact along the length of the cable.

Jason
 
Re: Short in XLR shield ?

Thanks guys.

I knew short wasn't the word for it but mental blank..

I left a new cable in place but if the studio owner is able to separate out the old cable for me, i'd love to spend some time with it. I'm convinced that the shield on both ends is intact from the pins through to where it enters the cable. and it beggars belief that an entire braid could come separated at one point but.. it could happen.

If I get the cable, i'll chop in 1/2 and keep going until I find the spot.

Andrew
 
Re: Short in XLR shield ?

You don't have a "short" pin on one XLR or the other that isn't making contact, do you? I've only seen it happen once, but a pin somehow became displaced in the insert, and no longer made contact. The same thing might happen at the female end of the cable too. Although once you disassembled the connectors I would think this defect would be obvious. I also agree that it's very unlikely that a Canare Star Quad cable could be stretched enough to break the shield without also breaking the inner conductors.

The weirdest cable defect that I've seen was AES foil shield cable that had random shorts between one conductor or the other and the shield. They were all near the inside of the spool (where the wire was rather squirrely anyway) and seemed to occur where a kink in the wire pushed through the insulation. It resulted in rather time consuming repairs to a mic splitter before it could be used.

GTD
 
Re: Short in XLR shield ?

andrew gissing said:
Thinking it could be a plug, I metered from the exposed solder at the back of the plug to the other side of the plug. Worked fine even moving around the meter inside the female plug.
Click to expand...

Like they say in Med School: When you hear hoofsteps think horses not zebras.

OTOH does anyone remember when Whirlwind had some plastic MASS W4 insulators than "went conductive" over time? That was fun...
 
Re: Short in XLR shield ?

Jim McKeveny said:
OTOH does anyone remember when Whirlwind had some plastic MASS W4 insulators than "went conductive" over time? That was fun...
Click to expand...

Not W4s in my case, but W3s. In at least one case the insert was NOS (from 1994) and went noisy when using phantom power.

Sharp eyes will notice that I replaced it with an even older Cannon part. The second insert was eventually replaced too.

GTD
 

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