First law of electronics:

"The $300.00 picture tube will blow first to protect the $0.25 fuse."

Although you may be lucky and find there is a fuse in this radio, the first
law will normally operate. I'd take an educated guess and say the
transmitter output stage is burnt out. If it transmitted for a few seconds
at this higher voltage, the heat generated in the output transistor will
probably have caused it to go open circuit.

As embarrassed as you may feel, it will help the technician that repairs it
to know about the cause! This could be reflected in a lower price to repair
than to just chase the problem around without knowing the cause. Most radio
gear will handle a partial overvoltage of 16 to 18 volts as part of the
normal operation expected with an engine driven alternator, the 28 or so
volts that has been applied would be well over any design expected event.

Hope this helps,
Peter

"Henning DE" wrote in message
...
Hello !

I have some trouble with a King KX 175B Nav/Comm Radio:
I have connected a 14 V Unit to 28 V Power.
(The aircraft has two voltage buses)
Interesting, it does recieve very good and the lamps wont burn out, but
once
you set it to transmit, thats it.
It will transmit once and then never again.
It still does recieve.

Did somebody out here made the same mistake ?
How can I fix it ? Is there a fuse inside ?
Any help is greatly appriciated.

Henning DE