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Electronic Theatre Controls Inc

R20 Modules are Unresponsive in a DR Rack


Circuits in R20 or R20AF modules do not turn on in a Legacy Unison DR rack, but their signal lights turn on as if they are active. You cannot hear an audible click from the relays when the signal light turns on.

Description/Explanation of Issue

R20s require a neutral reference to operate properly. This reference is provided by the signal distribution card via a wire connected to the neutral bus. If you see signal lights on your R20 modules, but there is no power to the circuit, you may have either a disconnected neutral reference wire, or your DR rack may be old enough that it does not have one at all. To determine the state of this neutral reference, power off your dimmer rack and remove the processor, then refer to the images below.

Do not remove the Unison processor or any dimmer modules without first powering off the dimmer rack at its breaker. Failure to do so may result in injury or damage to your equipment.

dr neutral ref with bus.png

The above image shows a properly-connected neutral reference. It should be securly soldered to the signal distribution card (shown in a yellow circle on the right) and the other end of the wire should be landed under a screw terminal on the neutral bus on the left (circled in orange). If the wire is not securely soldered to the card, contact ETC Technical Services for assistance.

dr no neutral ref.png

The above image shows a signal distribution card that does not have a neutral reference. Early DR racks do not have a neutral reference wire and the rack must be serviced for compatibility with relay modules. Contact ETC Technical Services for assistance if your card does not have a neutral reference wire.

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