Unless you feel confident it is strictly a mechanical problem , you could check for power at the windlass or any reversing contactor relay while someone presses the Down switch.
In their wisdom, Good does not appear to offer parts diagrams or trouble-shooting tips covering that issue online .
Do you know if the free=fall function is enabled ,say, just by energizing a solenoid to retract a spring loaded anti-reversing pawl from against a ratchet gear on the shaft?
Can free-fall be attained with an emergency handle or lever? Is this a 500 Rope Series model(in case someone else has whatever model you are asking about)?
Here's Good's number so you can inspect the horse's mouth. (609)698-4402