Tested each of diode pair fch20u10 with analog ohm-meter: directly-open but with bigger direct voltage conducts, inversely- resistance of 40 ohms! but I suspect it is ok or not because tested an ok mur1620 and it showed 100ohms I guess those fast power diodes should not show inverse resistance of Kohms?
Schottky diodes have a very low forward voltage drop. Normal silicon is .6 - 1.7 vdc while Schottky is .15 - .45vdc.
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It could be that your meter is not placing a high enough reverse voltage bias to completely turn off the junction.
The usual failure mode of high current rectifiers is short circuit (i.e. large reverse conduction). If this is out-of circuit, probably the diode is dead. A 'real' test, though, would require known voltages and currents, not just the 'ohms' value (a ratio of unknown voltage and current, whatever the meter manufacturer thought was best). If your resistance scale measures at microamps, the milliamp leakage specification might not be violated, but you'd never know it.
Is this a stud rectifier? If it is, are you sure the stud is the cathode? Some types come both ways.
common cathode
Common cathode only applies to multiple diodes in one package, with the cathodes tied together.
Reverse polarity stud mount diodes typically have the same part number, with 'R' appended to the end.
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