Originally Posted by KD8PIQ
I might need to check the source resistors, but I can't imagine them being bad.
I mentioned that...... Bad FETs are VERY often associated with bad source resistors, and/or bad 47 ohm gate resistors and bad protection resistors (2.2k in that unit).
You may as well ASSUME the protection is bad..... the parts are cheap. And a catastrophic failure often DOES kill some protection parts.
Also have a good look at the bias circuitry. The bias normally holds the gates about 5 to 8 volts apart (due to the "on " voltage for the FETs). If instead of 8V max, you actually do have the 140V total difference which you seem to be mentioning, it seems reasonable that the bias cannot possibly be good.