two NPN transistors

two PNP transistors

one NPN and one PNP transistors

two NPN and two PNP transistors

Open coupling capacitor

Open ON/OFF switch

Very high input signal level

Open bypass capacitor

random checking

checking step by step

trial and error checking

logical checking

signal generator

signal tracer

signal injector

any one of the above stated equipments

Open speaker coupling capacitor

Open output transistor

Open emitter bypass capacitor

All the above stated defects