Today changing out that control board.
Note in the pic below that there is nothing plugged into the 2 pin plug next to the plug for the rainbow cable from the mainboard, bottom left of control board.
What's not plugged in here is that ground wire that should connect to the neg battery terminal. Powerjack forgot to install one. I failed to notice that it was missing till now. Did that contribute to the hi voltage event/failure? Probably.
Pulled the old control board and noted that resistor 117-1 is blown out on the source board. Nothing else obvious so will probably get a new source board and lfdriver and test it out... someday.
In the first of the above pics, note the blown resistor 117-1 and two ribbon cable connectors for two mainboards. The replacement board (second pic) shows only one connector. I guess powerjack must have known I was going to use only one mainboard (I didn't tell them!).
So changed control boards and made sure of connections, including that ground connector plugged in. Crossed my fingers, connected to batteries, and turned it on. It runs!
Good sinewave. Not going to put this one on the house till I'm reasonably sure it won't blow my stuff up again. Loaded it with a 1500w heater plugged into the 110v receptacle and a 200w 220v heater plugged into the 220v receptacle. Ran that for about 3 hours. Voltage drifted about 2 or 3 volts.
Not as rock steady as I would like but not spiking high. Tomorrow I will run a cord out to my freezer in the garage and run it along with the heaters for a few hours. Something besides resistive loads.