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Problem found, I hope
My avionics guy, who is also an A&P/AI, helped me troubleshoot this problem (first one, then the other alternator going off line, intermittantly). After examining the schematic and listening to my description of the symptoms, he initially suspected the overvoltage protection unit, but we removed that and jumpered past it (on the ground), and the problem remained. He examined the voltages at that point in the circuit and decided the main isolation diodes (on the firewall center in the front, behind the warning light circuit board) were probably the culprit. We found that both diodes were loose in their bases, and one diode had a loose connection on the bottom of the diode as well. We tightened all these connections (easy to say, took five hours to disassemble, tighten, and reinstall), and everything seems to work great now. Since this is an intermittant problem, I won't really know if we fixed it for a while, but I am hopeful because it matches all the facts. "Whacking" the voltage regulator was also vibrating the diodes (right next to regulator), jiggling into better contact. The "laying on of hands" repair in Minnesota was the A&P feeling each wire in the bundle below the diodes, so in fact, he was applying force to the diodes.
Thanks Bob and Gmas for your suggestions, you both included the actual problem in your lists of areas for investigation.
Kevin
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