REPLACING ALL RESISTORS
My package from Digikey finally arrived after the fulfillment delays and then the snowstorm related delivery service delays. The next day I went to the workshop to swap in all the replacement resistors. These were the parts that had deviated from their nominal values which might have contributed to the misbehavior of the regulator.
INTERMITTENT FAILURE CONVERTED TO STEADY FAILURE
With the parts changed, the regulator now enters the same state that it only did on a repower before - where the output is down around 3V with oscillations, ballooning the current into the regulator required to drop 15V to 3V, resulting the the circuit breaker tripping. Previously the machine would power up fine when cold, run for a while, then if it were powered back up after only a few minutes powered down, this state would occur.
I choose to believe this is progress. A steady failure can be investigated and the root cause found. I have been trying to recreate the failure behavior by shorting or opening various components under LTspice but have not yet been successful. I will begin to remove the transistors and put them on the curve tracer so that I can spot any obviously defective such part.
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