OK, good news for now. It appears my problems were due to a water leak or condensation. Two fairly small areas or corrosion in opposite corners of the PCB (sorry, no pics!). A little work with q-tips, alcohol, eraser tip, DeOxit cleaner, and so far all is well. Unit wakes up as intended. Now just have to see if the fix holds. If this happens again, I may try coating the PCB in epoxy or something.