Hi there!

I used my multimeter to measure pins of a newly-bought SCR named S4006L. When I used the diode-checking mode, I hooked my probes across the cathode and the gate pin. Whether I swapped the probes, I always got 0.2V. Also, the resistance between those two pins is around 150 Ohms, even if I swapped the probes. Measuring the the capacitance between the anode and the cathode, I got a reading of 8pF.

Here are my questions:
1. When I hooked my positive probe at the cathode and the negative probe at the gate, why I got such a reading? If you see the equivalent circuit of an SCR, the cathode is an N-substance while the gate is a P-substance. This is obviously reverse biasing. Should it show high resistance instead?
2. I would like to know more about the capacitance. If you have any good resources, may I see that too?

Sincerely,
BlackMelon

 

From Wikipedia:

When I used the diode-checking mode, I hooked my probes across the cathode and the gate pin. Whether I swapped the probes, I always got 0.2V.

When probing diodes, you should mention how you have the positive and negative leads placed.

From the gate to the cathode, you can measure that PN junction. One direction (positive lead to gate, negative lead to cathode) it will be forward biased, and reverse biased in the other direction.

1. When I hooked my positive probe at the cathode and the negative probe at the gate, why I got such a reading? If you see the equivalent circuit of an SCR, the cathode is an N-substance while the gate is a P-substance. This is obviously reverse biasing. Should it show high resistance instead?

Meter or user issue.

2. I would like to know more about the capacitance. If you have any good resources, may I see that too?

There's a capacitance between each PN junction. The more you reverse biase the junction, the smaller the capacitance gets.

 

Could be they're bad. You should get a diode drop between the gate and cathode with positive on the gate and no drop the other way. It should be open between all the other connections without proper biasing.

 

Many thanks to you guys! I would rather check my multimeter instead, since the accuracy of the meters vary from one manufacturer to manufacturer. Anyway, I will also check the SCR by using it to drive a lamp, and see if it can latch after triggering its gate.