In order to use R20 (20A Relay Modules) in Unison Legacy DR racks, a signal distribution card with a neutral reference must be present.
To determine if your rack has a neutral reference signal distro card, you will need to first power down the rack entirely and remove the processor and the bottom few modules of the rack. The signal distribution card is the circuit board that runs the length of the right side of the DR rack. Near the bottom of this card you should see a small white wire soldered on if the neutral reference is present.
If your rack does not have this neutral reference wire then the signal distribution card will need to be replaced with a newer version. The neutral line cannot be connected to the older card as a solder location is not present.
To have a new card installed, please contact your local ETC dealership.
The parts needed are as follows:
For a DR6 7083B5604
For a DR12 7083B5603