On our 15xx, 16xx, 17xx, and MR-357 series, occasionally a tray is forced, or the dispenser has been used successfully for several years and then the tray will not rotate consistently. If you hear the motor run and the alarm sound, but the next dose of medication is not in the dispensing cup, the tray probably did not advance and this Replacement set of Gears will most likely resolve the issue. We have been successful in sending out replacement parts with easy to follow instructions. The customer or caregiver is able to make the repair in a few minutes and the unit will again operate as usual. Before ordering this part, insure the battery is installed as the unit runs off of the battery. The AC adapter trickle charges the battery. The unit will not rotate without the battery installed. If there’s any doubt as to the problem, please call MedReady at 310.328.7557 and we can diagnose the problem over the phone. M-F 9-4 Pacific.