In-Circuit Transistor Tester

46 IN-CIRCUIT TRANSISTOR TESTER by A. Rigby In electronic troubleshooting a transistor is generally not above suspicion until it responds correctly to the usual diode-tests with an ohmmeter. Before these simple test can be performed, however, the transistor must be removed from the circuit. Experience teaches us that this operation is time-consuming as well as possibly harmful to the PCB and the rest of the circuit in a good many cases, while it offers no guarantee that the cause of the malfunction will be found. The super-simple and inexpensive good/faulty indicator described here tests almost any transistor in circuit. A further useful feature of the tester is its built-in npn/pnp indication. The circuit shown in Fig. 1 is straight- forward and based on low-cost compo- nents. The central part is a dual J-K master/slave bistable Type 4027, ICI, of which one section, ICI., is configured as a multivibrator. The frequency of the symmetrical output signal is set to about 100 Hz by RI...