Alternator whine

Dave Anderer writes:

I'm looking for advice to help shorten the trouble-shooting process here.

My Arrow has developed an alternator whine over the past few hours. It
is *barely, barely" noticable on both radios when receiving, but loud
and obnoxious (both to me and other aircraft) when transmitting. No
doubt it is the alternator - switching the alternator off fixes the
problem.

So your first troubleshooting fork is this:

1) The alternator/charging system may be making more ripple than
before.

or

2) The ripple may be the same, but the comm system is doing a better
job hearing it.

For 1) two major suspects:

a) Bad grounds.
b) Bad diode{s}.

b) Is easy to {dis}prove with a o-scope; without it takes some
experience & judgement. One clue is it can't generate full current
when loaded. a) is usually diagnosed by inspection and cleaning the
connections; those being the battery ground, the alternator ground,
the engine-to-frame ground, etc...

2) Note that while the alternator IS the source; it may not be at
fault at all. The mike line should be grounded at one and ONLY
one place... An added, improper ground on a mike jack may make a
nasty ground loop.

That can be as simple as the insulating washers having slipped. Mike
jacks mounted in a metal panel may have insulating shoulder washers:

--|-- --|--- washer
| |
\-- --/ w/shoulder

-- --
-- -- metal panel
-- --

/-- --\
| |
--|-- --|--


The panel hole is bigger than the jack shaft. The shoulders sit in
the hole; holding the jack's shell centered away from ground.

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& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433