Jerry ...

I don't think that is going to be it. If the Grover diode is in parallel
with the input, yes, it will have blown the fuse and probably trashed itself
in the process. However, if that diode failed open, then the adapter will
work albeit without any protection. If it failed shorted then it will blow
the next fuse and according to the OP that didn't happen.

If that diode were in series with the hot lead, then all that would have
happened is that the diode would have been back-biased and not passed any
current. That didn't happen either as it did blow the primary fuse.

Most of those little adapters have switching power supplies inside of them
these days to buck the aircraft battery voltage down to whatever the radio
battery supply is plus a volt or so to back-bias the summing diodes in the
radio power supply line. Most likely it got zapped. Cheapest way to fix it
is buy a new one from Icom and learn from the experience.

Jim



You probably blew the protection diode---look for a little black thingie,
close to the input jack-that has burned up.