How to detect thyristor with the help of multimeter
There are two types of thyristors: one-way thyristors and two-way thyristors, both of which have three electrodes. One-way thyristor has cathode (K), anode (A), and control electrode (G). A two-way thyristor is equivalent to two single-phase thyristors connected in reverse parallel. That is, one of the unidirectional silicon anodes is connected to the other cathode, and its lead-out end is called T2 pole. One of the unidirectional silicon cathodes is connected to the other anode, and its lead-out end is called T2 pole. The rest is the control Pole (G).
1. Distinguish between unidirectional and bidirectional thyristors: first test two poles, if the forward and reverse measurement pointers do not move (R×1 block), it may be A, K or G, A pole (for unidirectional thyristors ) may also be T2, T1 or T2, G pole (for a two-way thyristor). If one of the measurement indications is tens to hundreds of 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 rest is the A pole. If the forward and reverse test indications are tens to hundreds of ohms, it must be a bidirectional thyristor. Then turn the knob to R×1 or R×10 and retest. There must be one resistance that is slightly larger. The larger one is connected to the red pen for G pole, the black pen is connected for T1 pole, and the remaining one is T2 pole. .
2. Difference in performance: Turn the knob to R×1 gear. For 1~6A one-way thyristor, the red pen is connected to the K pole, and the black pen is connected to the G and A poles at the same time. Keep the black pen from leaving the A pole state. Disconnect the G pole, and the pointer should indicate dozens 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 momentarily disconnect the A pole and then connect it again. The pointer should return to the ∞ position, indicating that the thyristor is good.
For 1~6A triac, the red pen is connected to the T1 pole, and the black pen is connected to the G and T2 poles at the same time. Disconnect the G pole while ensuring that the black pen does not break away from the T2 pole. The pointer should indicate tens to more than one hundred. ohms (depending on the current size of the thyristor and different manufacturers). Then swap the two pens and repeat the above steps to measure once. If the pointer indication is slightly larger than the last time by more than ten to dozens of ohms, it indicates that the thyristor is good and the trigger voltage (or current) is small.
If the G pole is disconnected while keeping the A pole or T2 pole connected, and the pointer immediately returns to the ∞ position, it means that the trigger current of the thyristor is too large or damaged. Further measurement can be made according to the method in Figure 2. For one-way thyristor, when switch K is closed, the light should be on, and when K is turned off, the light still remains on, otherwise the thyristor is damaged.
For a two-way thyristor, when switch K is closed, the light should light up, and when K is turned off, the light should not go out. Then reverse the battery connection and repeat the above steps. If the result is the same, it means it is good. Otherwise, the device is damaged.
