Norelco 6863 XL Razor

I have 2 of these models. The first one refused to shut off [continued on at full throttle] so I plugged it into power thinking that might trigger something to change state. Instead, there was a small "poof" and the power led turned "red." It worked corded a for a few hours and then died completely. The second unit is just now refusing to turn off [at least it slows down and gradually stops]. I disassembled the first unit and was unable to visualize any defect or find anything obvious with a multimeter. I did read the SER FAQs on Norelco. [Having used these for 40 years, I preferred the simpler models.] I'd probably have better luck if anyone has a schematic. Or any hints? Thank you.