The question becomes is the damage I described consistent with the likely
damage caused by hooking 24 volts into a 12 volt system?

There seems to be other things that were undamaged. Starter and alternator
appear ok, but then they were not in use when a GPU would be hooked to it.
Doesn't mean they couldn't have been fried anyway, but the last time I
remember this happening it was only radios that were damaged. No idea yet
if the transponder was damaged in anyway yet either.

Aren't airplanes fun LOL
"Ronald Gardner" wrote in message
...
Hooking +24 VDC to a +12 VDC system could most definitely cause major
damage to
electronic components!

Ron Gardner

mark wrote:

Well I had an old student that just got an education in radio shops.
He
has an older 172. He took the airplane in for a pitot static check and
to
certify a transponder. Spent all day there. First is that they came
back
and said he had a blind encoder that was bad, even though he got no
complaints from controllers on the way in.

When he got back in it to fire the airplane up, BOTH radios were also
dead.
They quickly looked at it and found a burnt out diode in one on the bench
and the other they kept to check.

All this is HIGHLY unlikely without some help. Then I asked does the
airplane have an external plug for ground power. hmm He said yes. Its
an
older 172 with a 12 volt system, but I suspect the shop hooked it up to a
24
volt ground power unit.

Would these symptoms be consistent with a young kid hooking a GPU up at
too
high of voltage? Hes learning that many shops you are lucky to get your
airplane back undamage, even if they don't fix what you took it there
for.
Thanks in advance.

Mark