How to use a multimeter to test thyristor

There are two types of thyristors: unidirectional thyristors and bidirectional thyristors, both of which have three electrodes. Unidirectional thyristors have a cathode (K), an anode (A), and a control electrode (G). Bidirectional thyristors are equivalent to two unidirectional thyristors connected in reverse parallel. That is, the anode of one unidirectional silicon is connected to the cathode of the other, and its lead end is called the T2 electrode, and the cathode of one unidirectional silicon is connected to the anode of the other, and its lead end is called the T2 electrode, and the rest is the control electrode (G).

1. Distinguishing between unidirectional and bidirectional thyristors: First, measure any two poles. If the pointers for both the forward and reverse measurements do not move (R×1), it may be A, K or G, A pole (for unidirectional thyristors) or T2, T1 or T2, G pole (for bidirectional thyristors). If one of the measurements indicates a few dozen to a few hundred ohms, it must be a unidirectional thyristor. The red pen is connected to the K pole, the black pen is connected to the G pole, and the remaining is the A pole. If the forward and reverse measurement indications are both a few dozen to a few hundred ohms, it must be a bidirectional thyristor. Then turn the knob to R×1 or R×10 and re-test. There must be a slightly larger resistance value. In this case, the slightly larger red pen is connected to the G pole, the black pen is connected to the T1 pole, and the remaining is the T2 pole. 

2. Difference in performance: Turn the knob to R×1. For 1~6A unidirectional thyristor, connect the red pen to the K pole, and the black pen to the G and A poles at the same time. Disconnect the G pole while keeping the black pen attached to the A pole. The pointer should indicate several tens of ohms to one hundred ohms. At this time, the thyristor has been triggered, and the trigger voltage is low (or the trigger current is small). Then disconnect the A pole instantaneously and connect it again. The pointer should return to the ∞ position, indicating that the thyristor is good. 

For 1~6A bidirectional thyristor, connect the red pen to T1 pole, and the black pen to G and T2 poles at the same time. Disconnect G pole while ensuring that the black pen does not separate from T2 pole. The pointer should indicate dozens to more than one hundred ohms (depending on the thyristor current and manufacturer). Then swap the two pens and repeat the above steps. If the pointer indicates a few dozen to dozens of ohms more than the last time, it means that the thyristor is good and the trigger voltage (or current) is small. 

If the pointer returns to the ∞ position immediately when the A or T2 pole is connected and the G pole is disconnected, it means that the thyristor trigger current is too large or damaged. Further measurement can be performed according to the method in Figure 2. For a unidirectional thyristor, the light should be on when the switch K is closed, and the light should not go out when the K is disconnected, otherwise it means that the thyristor is damaged.

For a bidirectional thyristor, close switch K, the light should be on, disconnect K, the light should not go out. Then reverse the battery and repeat the above steps. If the result is the same, it means it is good. Otherwise, it means the device is damaged.