Zener diode working performance quick test circuit

As shown in the figure, VT1, VT2, etc. form an astable self-excited multivibrator, and its oscillation frequency is determined by C1, R2, R3, C2, etc. The period of this oscillator is about 4 seconds. When VT2 outputs a high level, VT3 is turned on after VD shaping, and the current is limited through the light-emitting diode H1 and the resistor R6, triggering the bidirectional thyristor VS. The normal thyristor VS is turned on immediately, and the light-emitting diode H2 emits light; when the VT2 output is low level, VD and VT3 are cut off, VS is cut off, and H2 does not light up. H1 and H2 flash synchronously, which proves that the thyristor is good; if H1 flashes and H2 is always off, it means that VS is internally open; when H2 is always on, it means that VS has an internal breakdown; when H1 and H2 do not flash, it means that VT1, The VT2 circuit does not vibrate. This circuit can also measure diodes. When measuring, insert the positive pole of the diode into X1 and the negative pole into X2. If H2 lights up, the tube under test is good; plug it in the opposite direction and H2 should not light up. This circuit can also measure triodes. Insert the base of the transistor into X3, the emitter into X2, and the collector into X1. If normal, H1 and H2 will flash synchronously.