Maintenance in NEC 2400 IPX is little complex, all results will be in hexadecimal, it takes time to debug the error and average person cannot do that. But there is a simple maintenance feature that helps us to test phone without assistance.
This phone test lets you to test your phone ringing just by dialing a simple code, once you do this your maintenance becomes less difficult. How you do that, the common way to test the extension is asking someone to call back the extension to check the ringer circuit.
Assign an access code for Individual trunk access. From single line telephone dial the individual trunk access code and followed by 999, hang up. Your telephone will start ringing. Henceforth you don't require any one to give you a test call.