A s.s. head-scratcher

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Original poster: Ken or Doris Herrick <kchdlh@xxxxxxxxx>

Steve Ward et al-

This one stumps me but perhaps not someone else:  I'm implementing my 
push-pull s.s. primary circuit, using two Powerex CM300DY-24H 
IGBTs.  Previously it appeared to function but not satisfactorily so 
I've redesigned and rebuilt the drivers.  Waveforms now, right at the 
IGBT gates, appear perfect.  However...  The IGBTs will conduct no 
current; nada, zip, neither of them.  Nothing within them is shorted, 
per my ohmmeter, and the gate:emitter nodes are "open" per the ohmmeter.

In order to accommodate my revised driver circuit, which has 
back:back zener protection, I had carefully removed the 10K resistors 
that were protecting the gates.  Was I not careful enough, do you 
suppose?  Could the gates have actually opened up within the 
packages?  >Both< of them??  Not hardly, I should think: they'd be 
shorted, if anything.  Does anyone have a clue, before I have to 
un-mount them & jury-rig a test-setup?

Ken Herrick