A controller with a partial or blank display usually has damage to an electronic component on the internal circuit board. Normally this type of damage cannot be repaired. If the controller was installed outside be sure that the door remains closed completely when left unattended. Moisture intrusion is one of the more common reasons this problem may occur.
On some Hunter controller's a 9 volt battery can be installed in the face panel. A working face panel will display a NO or NO AC message after a fresh 9 volt battery is installed.