There seems to be some confusion about how an
opto-isolator affects a
DMX signal. The vast majority of them (all that I know of) are simple repeaters: whatever data you put into it is exactly what you get out of it. There's no buffering and regenerating involved. If there was an issue with the refresh rate of the
console, adding an
opto would not make any difference since you'll get data out of the
opto at exactly the same rate.
Given the state of wiring in this particular facility, that would certainly be my first place to look for problems. It very well could be a grounding issue. If that's the case, then leaving the optoisolator connected is probably the simplest solution for you. You may also have the Data+ and Data- wires swapped somewhere, or one of them may be disconnected. Those problems would be less likely to be fixed with an
opto, but they're something to check for.
You may also have a marginal
DMX transceiver chip in the
console. Have you tried using either of the other outputs? The transceiver chip is a 75176 (
available from Digikey and others) and it's quite easy to replace on the Expression 3. Feel free to PM me if you want further instructions or pictures.
As with any problem involving
ETC gear, your best resource is their phone support staff. They'll be happy to talk you through any problem from 8-5 central time on weekdays, and have someone available 24hrs for emergencies:
1-800-688-4116