Hi all,

I recently came into possession of some spare (power) components, one of which is an hockey puk type SCR from 2016 - N0782YS160 (datasheet attached).
Wanting to check whether the SCR is still good but not having any experience with this part I followed this tutorial:

From what I gather the anode-to-cathode resistance when compressed should be in the 20-30 MOhm range, while the cathode-to-anode resistance
should be slightly lower, in the 10-20 MOhm range. When a gate current is applied the tutorial shows a lowering of the anode-to-cathode resistance
to around 1 MOhm and stops there since to properly test it further (the latching behavior) a higher current source/load is needed, this is clear to me.

When testing my SCR in the same way I found an anode-to-cathode resistance of 600 kOhm and cathode-to-anode about 1.4 MOhm.
When applying a gate current the anode-to-cathode resistance seems to start dropping significantly at around 30 mA of current, the minimum achieved
is around 40 mA gate current with anode-to-cathode being around 180 kOhm, if I increase the gate current further then the anode-to-cathode resistance increases back up. I suspect this is due to the latching characteristic of the SCR, so basically I start turning it on but due to there not being any
current from anode to cathode the resistance goes back up. Please correct me if I'm wrong.
Also in my case, this behavior is not affected by compression (I checked it with a woodworking clamp).

Basically my question is whether this SCR is improper/internally shorted, if I should check something else, or if I'm doing something wrong.
My multimeter can only measure up to 2 MOhm ...

Thanks

 

Basically my question is whether this SCR is improper/internally shorted

Testing resistances of semiconductors is not a good method. What you want is a functional test.

Put in a simple test circuit with a load connected. If the load is on immediately, it is shorted.

Now trigger the gate. If it does not turn on, it is open. If it turns on and stays on after the gate current is removed, it is functional.

 

Here is the suggestion from an early GE Experimenters manual.

 

Thanks for the quick reply @BobTPH and @MaxHeadRoom,

I will rig up a test circuit as you guys mentioned and go from there.

 

How to mount "tablet" SCR on heatsinks - see here:
https://kron-ek.ru/sila/ohl003/
https://kron-ek.ru/sila/ohl006/

 

I rigged up a test circuit with a variac (rectified output) and a lamp load - my conclusion is that the SCR works properly.
The SCR was clamped during the tests, I didn't test it unclamped since in that case it's difficult to make
a proper connection to the cathode (when clamping I used small protruding metal flats on both sides of
the SCR to get a surface for the alligator clips/cables).

Without gate signal anode -> cathode is open (no current, load is off), once the gate is triggered
the SCR conducts and the lamp lights up, and when I reduce the voltage on the variac so that current < holding current
it refuses to conduct until I trigger the gate again.

What I did notice is that the SCR is still conducting with a current of 200-300 mA while the datasheet specifies a
holding current of 500 mA, but that's not too important to me personally.

Thanks for the input guys, appreciate it.

 

while the datasheet specifies a
holding current of 500 mA,

That is likely the minimum current they guarantee will hold. If it holds below that, it is mot out of spec.