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How to test an scr with a multimeter

How to test an scr with a multimeter


This publication deals with the testing of thyristors - silicon-controlled rectifiers - using an ohmmeter.

How to test an scr with a multimeter

A pin assignment diagram for thyristors in a TO-220 package is provided for reference.


Testing SCRs with a multimeter
Identify the ohmmeter terminals.

Using a junction diode we can tell which ohmmeter lead is positive and which is negative.
Connect a generic PN diode to the positive and negative terminals of the ohmmeter.
The ohmmeter will only show continuity if the positive lead is connected to the anode of the diode and the negative lead is connected to the cathode.
Based on this concept, SCRs can be tested with an ohmmeter.
Procedure for testing SCRs with an ohmmeter.

To test the SCR, connect the positive lead of the ohmmeter to the anode and the negative lead to the cathode.
The ohmmeter should not show continuity.
Touch the thyristor gate to the anode.
The ohmmeter should show continuity at the SCR.
When the wire is removed from the anode gate, the wire may break or continue, depending on whether the ohmmeter is providing enough current to keep the device above the holding current level.
If the ohmmeter indicates that there is continuity at the SCR before the gate touches the anode, the SCR is shorted.
If the ohmmeter does not show continuity at the SCR after the gate touches the anode, the SCR is open circuit.

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