Crossed wires

[RedDog]

So, bit long winded but....

5 LED uplighters on stage, DMX controlled, working fine for over a year suddenly started behaving erratically, random flashes. also caused PARs on dimmer pack to blow due to this random strobing.Individually tested each LED, swapped DMX cables and found that someone had rolled our 1 ton piano over the DMX cable that runs across rear of stage, replaced cable, re-plumbed everything, replaced blown PARs.All working as it should.Now, after repairing damaged cable that was shorting out, cut beyond damage and resoldered XLR, discovered that the XLR plugs on each end were connected differently, ie.. male pin 1 to female pin 1, male pin 2 to female common, male common to female pin 2. I know that in an audio cable this could be an issue, but it seems not to be an issue in the DMX cable. Is this the case?

 

 

[david.elsbury]

“ male pin 1 to female pin 1, male pin 2 to female common, male common to female pin 2. “

 

Sorry? We are talking 3pin XLR yes?

 

On an XLR pin 1 is always common and 2/3 are the signal pins. For audio pin 2 is typically hot and for DMX pin 3 is hot (as per the standard)

 

So; how are your cables wired? Can you use the PIN numbers to make this description clearer?

 

Typically if DMX has a crossed over data pair (pins 2&3) I wouldn’t expect it to work but it would depend on your equipment obviously

[DrV]

There must be another swapped pair somewhere which is reversing the swap on the cable you're looking at. There's no way that DMX would work at all if data+ and data- were swapped.

[alistermorton]

Makes you wonder if it was a special cable for an old Martin fixture at the end of a line?

[timsabre]

I wonder if he might mean that the DMX "hot" is connected correctly, but "cold" is cross linked to gnd. This would probably work ok, though the DMX driver at the source end is going to be a little unhappy. DMX will generally work fine with just the hot line connected and some type of ground reference.

[RedDog]

So,I have connected the pins correctly. It was while testing I got the strange readings.... Checked again and - user error... I had both ends in one hand and tested for continuity by going - left female to left male as I looked at the plugs.

When of course it would be mirrored. Dick.

Thanks for your input, as usual.

 

 

 

[david.elsbury]

Easy mistake to make. If in doubt most reputable plugs and sockets have the PIN numbers moulded into the ends

[RedDog]

Easy mistake to make. If in doubt most reputable plugs and sockets have the PIN numbers moulded into the ends

[sunray]

Easy mistake to make. If in doubt most reputable plugs and sockets have the PIN numbers moulded into the ends

I have known a whole 48 way XLR patch cable (4U plate at each end of a cable in racks) wired with a 1/2 flip and it had been in use for a couple of years before I tried running a phantom powered mic.

 

 

The installers had blamed the noise on the cable route as the multicore ran through a very large plant room and a busy cable riser.

 

It took me less than an hour to correct it.

 

And the conferencing system on a boardroom table (XLR's mounted in table for gooseneck mics) XLR's wired incorrectly and the correction made in an EDAC so the cable screen and red wire were flipped at the back of the rack. Again it had been like it for a while with constant conplaints of noise on audio but I suspect there was no data or video running when inspected.

 

 

Yes a very easy mistake to make especially when wiring a mixture of male and female chassis mounted connectors.

 

[timsabre]

Once had a batch of neutrik-clone connectors with the wrong numbers moulded into the plastic. That took a bit of figuring out.