Since the Mio+ wouldn't boot, I suspected too low input voltage from the AC adapter while using it in my RV. Original AC adapter output voltage measured 12.12V, no load. I tried inputting 13.8 V DC, positive center pin. This produced smoke from the right side of the case when looking from the front.

On opening the Mio+, I found just one user serviceable electronic part: a small 330 uF (could be a decimal in that value somewhere) electrolytic capacitor across the DC input plug. All else is surface mount. A thing of beauty. The electrolytic doesn't appear to be physically damaged.

At this point, I still don't know if the Mio+ is actually damaged. But smoke and damage usually walk hand-in-hand.

Besides advising to carefully put the Mio+ back together, anybody have any tips at this stage?