Not usually the chopper on a nodrain situation. On this series, I usually find a blockage at the drain outlet (#15). There's a small plastic ball in there that acts as a backflow preventer. Sometimes debris can get in there. Remove the hose and this white plastic assembly will unscrew from the pump base.
Also disconnect the drain hose at the disposer or wherever so you can monitor the output into a pail. If you have recently replaced the disposer, be sure the drain plug is knocked out.