Avionic question for Mr. Jim Weir

I have some questions rather than jumping to conclusions...


-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)

Do you mean that you connected the 14 volt radio to the 28 volt bus and then
powered it up? If so, what do you mean by saying that the aircraft has two
voltage busses? That there is a center-tapped 14 volt bus and you connected it
to the 28 volt bus by mistake?


-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.

Do you mean that every time you turn the radio off and then back on that it will
transmit once and then not again? Or that it transmitted once when it was
powered up to 28 volts and that it now will not transmit at all?

Jim



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

"Jim Weir" schrieb im Newsbeitrag
...
I have some questions rather than jumping to conclusions...


-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)

Do you mean that you connected the 14 volt radio to the 28 volt bus and
then
powered it up? If so, what do you mean by saying that the aircraft has
two
voltage busses? That there is a center-tapped 14 volt bus and you
connected it
to the 28 volt bus by mistake?

Well, Jim, it is kind of a mistery to me. The Aircraft is a old six
cylinder C 172 (around `67 or so). On one of the avionics fuses has 28
Volt while the rest of the electrical system is 14 Volt. I did connect the
14V radio to 28 Volts.

-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.

Do you mean that every time you turn the radio off and then back on that
it will
transmit once and then not again? Or that it transmitted once when it was
powered up to 28 volts and that it now will not transmit at all?

When I first powered up the radio everthing looked fine. I had a wattmeter
in the coax line to the comm antenna. When I pressed the mike key the first
time there was a power output ( about 5 watts) to the comm antenna. When I
pressed the mike key again, there was nothing and it stayed that way. The
radio does not transmit anymore.

Henning

Jim



Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com