[John Hoffman]

I was flying a localizer approach this week when the no.1 nav com. dropped off line. There was no intermittent operation, it just stopped and no flipping of switches, breaker ect. would bring it back. I was considering switching no. 2 nav com, an identical unit,to no. 1 as a quick way of troubling shooting the supply circuit but in "googling" this radio for info and units for sale I never saw a24V unit. Are all MX170Bs 12v - Im cncerned that Cessna had some kind of voltage step down device that could have failed , if so the no.2 or a replacement radio could get "fried" . Any advice on how to proceed would be a big help.