How can i test an SCR in a servo control circuit with only a DVM and O'scope.475 volts,1/2 wave ,60 AMP 4 quad

Assuming that you are not removing the SCR from the circuit.


Try to look at the gate signal and the output at the cathode on a double beam 'scope while the servo is trying to operate. Or disconnect the gate and try to turn the SCR on from an external source and see if you get output motion from the servo or whatever the output is.Some caution required with 440 v !!Some recollection from 25 yrs ago may help ? Making a bridge or H-switch to drive a 1/2 hp dc motor. Collected a pile of dud transistors on bench until able to prevent simultaneous turn-on down one side of the bridge. This is prevented by correct commutation and ensuring that during switching, the instantaneous power dissipation in the device remains outside the specified region.Commutation is aided by placing an air-core inductor in series with the load and then usng a secondary winding on this to make sure that when one side is conducting that the other arms are turned off.It is somewhat tricky and very critical.How can i test an SCR in a servo control circuit with only a DVM and O'scope.475 volts,1/2 wave ,60 AMP 4 quad
With no power applied check each section, between its gate and cathode connections, on the ';diode'; range of the d.v.m.





They should read like a diode, i.e. one way they conduct and give a reading of the forward voltage, and the other way they should indicate high resistance or open-circuit.





Between the anodes and cathodes they should all read very high resistance or open-circuit in both directions.