Topcon CT-80 non-contact Tonometer
Defect: NG- / NG+ is displaying on screen after air check
The internal pump has failed, is clogged, or is dirty- preventing fluid movement of the pump to force air through the nozzle.
Attempt air-check procedures five times consecutively. If problem persists, the pump will most likely need to be replaced.
If above solution does not resolve defect, the device will most likely require service or repair.