Gilles.Thesee(at)ac-greno
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 Posted: Sun May 27, 2007 8:47 am Post subject: How to (sc...) ruin your VHF |
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Hi all,
Recently a buddy building a microlight asked for some help wiring his
electrical circuit. He had already installed everything on the panel.
The wiring went well until a few days ago when powering up the brand new
Microair 760 VHF and PM-501 intercom. While the VHF back light was
glowing, the VHF display remained blank and nothing worked.
After checking every wire in the circuit, much head scratching, and
enduring some veiled accusation of inverting polarities, etc., I called
the seller and brought him the Microair. He diagnosed a blown internal
fuse, due to some overvoltage or polarity inversion. But he was gracious
enough not to openly saying I was the culprit...The VHF was quickly
tested on the bench, with a dummy antenna load.
Back to the hangar I double-checked the supplied harness and my wiring,
opening every thermosleeve to make sure nothing was wrong, then my buddy
reinstalled the radio. Same behavior : the VHF display stays blank,
while the intercom works as expected.
This time I removed the VHF from the panel myself, and guess what ? My
buddy had changed the supplied black screws for SS socket screws more to
his taste. And those screws seemed very long. Indeed looking into the
screw holes, the PC board seemed very close...
I reminded my buddy of the red notice in the manual about the screw length.
Back to the dealer again, and indeed, once the radio was opened, we
could clearly see where the screws had damage the PC board. The internal
fused was changed once again, and the radio tested on the bench, but in
the aircraft (without the screws...), the display was OK, but all I
could hear was a garbled local music broadcast and no aviation transmission.
The little VHF will have to be sent to an approved avionics repair shop...
Morality : read the manual, and do NOT change the screws....
Best regards,
Gilles Thesee
http://contrails.free.fr
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