The Issue
Following a sudden grid transformer surge in Ajwa Road, an inverter AC went completely dead with no power to the indoor display unit.
Diagnostic
Testing revealed a blown primary line fuse, burnt varistor (MOV surge suppressor), and damaged optocoupler circuit communicating with the outdoor compressor.
Engineering Fix
- Replaced the blown surge protection network and safety fuse.
- Re-soldered new optocoupler chips to re-establish clean bidirectional communication between indoor and outdoor PCBs.
- Installed external surge protection to prevent recurrence.
Result
Power was restored and normal compressor cooling was achieved without waiting days for a replacement board from the manufacturer.