Is the DMX terminated?

Many people treat the fitting of a termination resistor as optional; even though DMX may work without it, in this state a small change to the DMX network, like adding another cable, may stop the system from working or cause intermittent effects like flicker of dimmers, twitching of moving lights and so on. Adding termination can help eliminate these effects.

Are you using the proper cabling?

When it comes to DMX cabling I know that many people use standard microphone cable instead of DMX cable, this can be the reason for problems when they occur. DMX512 is designed to be run with a cable at an impedance of 120 ohms, this impedance is similar to that of a standard cat5 cable used primarily for computer networking. Standard microphone cable has a lower impedance and higher capacitance than DMX cable, this could cause a change in the wavelengths of the DMX signal resulting in lighting issues. Most of the time, short runs of microphone cable will not cause problems, however, when long runs are used, your best bet is to use the proper cable type.

Is the cabling OK?

DMX may continue to work partially even under extreme conditions like having one half of the data pair broken. If you have a fixture which is misbehaving, take it and connect it directly to the DMX source with a short jumper cable. If it now works there is an issue with your cabling to be investigated.

Is the polarity OK?

Polarity on the DMX shutter or any DMX receiver is very important, if your using the non-compliant 3-pin XLR connectors and/or making adapters, pay close attention to the polarity. The pin-out for the RJ-45 connectors on the shutters are:

1. Data 1+
2. Data 1-
7. Signal common (ground or shield)