It works again!
It works! at least, it does right now.
So here's what I did. I brought the audio panel home, disassembled it mechanically, looked for any distressed electrical parts, said the correct incantation ("Wow, look at all those tiny little components!"), put it back together before I either forgot how or lost a part, put it in the back of the SUV along with a 12 pack of soda, went to Sunday school and church (don't think that had anything to do with it), and went out to the airport.
When I reinstalled the audio panel, it was in backup mode, but at least Clearance Delivery responded that the comm was loud and clear. But no lights, hence, no power... at least the plane is still flyable.
So I decided to see if there was power to the unit. The installation manual said which pins were power, but didn't give a picture of the connector with pin numbers. Found that on the web, but was unable to reliably reach the correct pin, no matter what Rube Goldberg assortment of improvisations I tried.
So I put the audio panel back in and then, in a stroke of inspiration, wondered if the unit was turned on or not. I pushed the power knob, and it came to life!!
I was wondering if the problems might have been the unit coming loose from the connector in flight, and that seems plausible except that my headphone and mike continued to work after the audio panel went into fail safe mode. If it had been loose connectors, I would not have been able to use the radio.
Anyway, late last week I went looking for a good deal on a pin-compatible replacement (rewiring the plane would require lots of time and bucks to have a shop do it, so pin compatible was a major consideration), and found a new in the box Garmin 245 at a very good price. Differences are that the Garmin has 3D audio (great for side by side and with two radios), but the present PS unit has a MONitor button which gives comparably useful two radio capability. But I only have one radio. The Garmin has Bluetooth and a USB port on the front, the PS has a 3.5 mm audio plug. Audio cables are more flexible but don't provide power to the unit. So the units are different but comparable.
The Garmin does have a clearance recorder, but the manual doesn't say what it records or really how to use it. It also says that if power is removed from the unit (low voltage during engine start, maybe?), all the recordings are lost. Very few vendors these days have manuals that really tell you what you need to know...
Anyway, I'll probably sell the PS unit at a good discount (About $1200 new, IIRC, although this one is out of production) and go with the Garmin unit, just for the sake of reliability. PS doesn't sell a separate install kit, but the Garmin install kit is about $125. And the Garmin should arrive this week.
Anybody want a PS Engineering audio panel that works fine?