Interesting. This just came up on another discussion board. I stated I'd never heard of an A4M with a 120Ω resistor between pins 2&3.
The board received the following answer:
"Ok, so the OFFICIAL response from the Wybron engineering dept is that you should terminate the power supply just like any other
DMX fixture. No termination of the scrollers is necessary."
Dusty Hudgins
Sales Manager
Wybron, Inc.
719-884-6480