How to determine the cause of the identified thyristor​ damage?

How to determine the cause of the identified thyristor damage?

When the thyristor needs to be inspected and analyzed for its cause after being damaged, the tube core can be removed from the cooling jacket, the core box can be opened, and the chip can be removed to observe the traces of damage to determine the cause. Analyze several common phenomena as follows:

(1) Voltage breakdown. The thyristor is damaged due to its inability to withstand voltage, and there is a smooth small hole in its chip that sometimes requires an magnifying glass to be seen. The reason may be a decrease in the withstand voltage of the tube itself or a breakdown of high voltage generated when the circuit is disconnected.

(2) Current damage. The trace feature of current damage is that the chip is burned into a pit, rough, and located far from the control electrode.

(3) The current rise rate is damaged. Its traces are the same as current damage, and its location is near or on the control pole.

(4) Edge damage. He occurs at the chamfer of the outer circle of the chip, with small smooth holes. Using a magnifying glass, you can see fine metal scratches on the chamfered surface. This is caused by the manufacturer's careless installation. It causes voltage breakdown.

(5) G-K voltage breakdown. The thyristor G-K is damaged due to inability to withstand reverse voltage (12V), and there is a burnt path (short circuit trace) between its chips G-K.