Stacker bin test Block the upper optical sensor and observe the movement of the stacker bin. Face-up bin full sensor test Lift and hold up the bin-full flag until the user LED blinks amber. The user LED should blink amber within a few seconds. Stacker Bin Full Sensor Test Block the upper optical sensor until the stacker bin reaches the bottom of its motion, triggering the stacker bin full sensor; the user LED should blink amber. EN 3,000-sheet stapler/stacker troubleshooting 489