A brief update from this afternoon's investigations:
- After returning from Fry's, we replaced the blown 50uF electrolytic cap in the PhaseA's Elgar amp. Since the unit was open, we went ahead and connected the neutral wire to the primary side in PhaseB Elgar. Also connected test wires to PhA and PhB's internal amp rail supplies +44 VDC, -44VDC, and ~2.5Vrms amp input sine wave. (All of these internal Elgar signals appeared AOK during loaded operation!)
- Turned 1401 on: 200 usec glitch still in PhB waveform and the fuzz still in PhA, BUT the glitch vanished when Ron pressed the 1401's "power off" switch (which controls a relay, currently supposedly out of the circuit, but oddly buzzing), and, as a bonus, the fuzz goes away while holding down the "power off" switch.
So I'm now fairly certain that the glitch and fuzz are due to some problem with AC power control circuit/relays in 1401/1402. (This time we removed the 3 fuses to the phase sequence relay inputs, so it was truely not potentially effecting phase voltages.)
- Building input phase currents were still high on RMS amp meter (~25A per phase), but this time we measured the waveform on the scope (across 10-ohm resistor at output leads of meter's clamp-on current probe). As Grady expected, it's not a pretty sine wave, but instead has sharp +50A peaks and -50A valleys. So I think the non-sinusoidal current is merely irritating the 30A panel circuit breakers. I'll contact the electrician about upgrading to beefier circuit breakers.
I'll email today's new scope pictures out on Monday morning ... . - Robert