Our technicians at firealarm.com have encountered various issues with the Simplex 8565-479 unit before. One common troubleshooting step is to check the input power to ensure it’s within the specified range. Sometimes, fluctuations or inconsistencies in the input power can cause the unit to malfunction. Additionally, inspecting the wiring connections for any loose or damaged connections can often resolve issues with this power supply unit. If the problem persists after these steps, it might be necessary to replace the unit or consult with a certified technician for further diagnosis and repair.