Thanks for the help everyone. It sounds like its totally consistent that
the type of damage that was done was consistent with plugging a 24 volt gpu
with a 12 volt airplane. Thanks again.

"pTooner" wrote in message
...

"Ronald Gardner" wrote in message
...
A motor Such as a starter will not be affect with this amount of over
voltage.
However, electronic components such as diodes, IC's, resistors are
another
story. It would depend on the protection built into the radio or GPS or
transponder that would clip the over voltage situation. If it is not
there,
then damage most likely will happen.

I completely concur. The most likely thing to blow would be the diodes
in the radio power supply. I too have many years in the military game.
(Retired avionics tech)

Gerry

Spent many years in USAF flight simulator
repairing electronics' in just such a situation. The best I ever saw was
later
when a fellow worker over voltage a $40,000 X-ray control panel, blew the
tops
off every IC!! A bit different though, he dropped a test lead against
the DC
trace. The other end was on one leg of a 480 VAC terminal!

Anyway, what you describe is highly probable , a tech not familiar with
older 12
VDC systems would out of habit go right to a 24 VDC hook up. With no real
problems going in and multiple failures coming out, the only common
factor is
the repair center and what they did! Did you put the repair on a credit
card?
If so, call them and dispute the charge and explain what happened, they
will
stop payment until resolved! Then at the same time call the repair
center and
speak to the top dog only. Tell them what happened and what you suspect
the
cause was. If flat refuses to except any of it, tell him you have
stopped
payment to him by the card company. And you will take the plane to
another
repair center for a check out and verification on your suspicions.

I think if they have any reputation to uphold, he will immediately make a
correction or have an explanation why that could not happen. Take good
notes,
then call and ask someone else if what they say is true.

mark wrote:

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