Tests transistors and diodes for polarity. A three-phase wave form is derived from the 350Hz ring-of-three oscillator formed by IC1A, IC1B and IC1C, and applied to the device under test via the LEDs. The oscillator wave form enables each pair of device terminals to be forward, reverse and unbiased for one third of a cycle.
Simple circuitry - 9V Battery operation.
Current flowing into the device will turn the appropriate Red LED on and current flowing out will turn on the Green LED. Thus, the position of the Base lead and the polarity of a transistor may be deduced.
IC2A, B and C are used to switch R7, R8 and R9 a