Don Allen Posted October 7, 2014 Share Posted October 7, 2014 One way DMX input ic's can be fried is when someone plugs a talkback lead (3 pin) into a DMX run, as the talkback has 30V on it. Link to comment Share on other sites More sharing options...
Tomo Posted October 8, 2014 Share Posted October 8, 2014 And that is one of the reasons why the standard prohibits the use of 3-pin XLRs for DMX. Link to comment Share on other sites More sharing options...
alistermorton Posted October 8, 2014 Share Posted October 8, 2014 One way DMX input ic's can be fried is when someone plugs a talkback lead (3 pin) into a DMX run, as the talkback has 30V on it. And pluggin a talkback lead into a rack of interconnected dimmers could easily take all of them out, if the in and out sockets are simply looped through. Link to comment Share on other sites More sharing options...
Stuart91 Posted October 8, 2014 Share Posted October 8, 2014 Could a phantom powered mic circuit cause the same problem, or is there not enough current available to do any damage? Link to comment Share on other sites More sharing options...
timsabre Posted October 8, 2014 Share Posted October 8, 2014 Could a phantom powered mic circuit cause the same problem, or is there not enough current available to do any damage? Not enough current. Phantom is fed through a 4.7K resistor and the DMX chips are fairly well protected internally. They are limited to 12V, so a 24V comms PSU would definitely do them some damage. However, they often fail in a short circuit state so they kill the rest of the DMX line (including stuff before them). Not sure why in this case the equipment before the dimmers would continue to work, unless the dimmers have an active buffered output rather than the normal pass-through arrangement. Link to comment Share on other sites More sharing options...
dbuckley Posted October 8, 2014 Share Posted October 8, 2014 Slightly Years ago, when Pulsar began misusing 5 pin XLR for DMX by putting power down the "spare" pins, they claimed to have published a protection circuit that would protect DMX chips well, but I never saw it published. Does anyone have it? Link to comment Share on other sites More sharing options...
timsabre Posted October 9, 2014 Share Posted October 9, 2014 Yes, and I use something similar when I design DMX interfaces. It was 2 PTC thermistors in series with the DMX lines, then a 5v clamping transient protector down to ground on each line. If you get a high voltage on the line, it goes to ground via the transils and heats up the thermistors which go high resistance and effectively isolate the line. Pulsar's original design used 240v rated thermistors and you could put mains on the DMX without damaging it. I did test this (rather nervously) and it was true. Link to comment Share on other sites More sharing options...
Womble Posted October 21, 2014 Share Posted October 21, 2014 It seems like you're trying the right things here. Have you got a multi function cable tester? I have one of these and I find it invaluable when it comes to fault finding! http://www.ebay.co.uk/itm/Universal-Audio-Video-Lighting-Cable-Multi-Tester-Tenma-72-8785-9-Plug-Types-NEW-/370693976046?pt=UK_Musical_Cables_Leads_Connectors&hash=item564f152fee Where abouts in the country are you? Perhaps a second pair of eyes would help. If you were near me I would be willing to swing by and take a look. Link to comment Share on other sites More sharing options...
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