Startec Arcbeam 150s

Yeah, no luck finding those manuals.

As has been said many times before:

Master/slave mode is 100% incompatible with DMX mode. It's OK to set them all to the same DMX channels so they all behave the same though.

Check your cabling and your polarity. Ensure you're using DMX cable and using a DMX terminator. Test them one at a time to isolate the one or ones causing the issues, although it is entirely possible they are all bad in their own ways. Also, check your DMX addressing and double check you're in DMX mode.

You might open them up and spray some contact cleaner in there in case it's a dirt issue.

thanks Chris

it's been awhile since I soldered the original cable(s) for correct polarity, so i'll take you up on your advice and re-confirm i haven't inadvertently substituted different cords

can you or anyone shed light on whether these particular fixtures were excessively problematic back in the day? Or were they mostly reliable?

I'm all for admitting operator error, if I can get them back up to spec...

I have no direct experience with the fixture you mention, so I just thought I'd pass along some general troubleshooting advise.

All I can say is that I've been inpressed with the reliability of my ADJ fixtures. I know that's not very helpful for you though.