> Hi Guys,
>
> After four years of satisfactory service in my Europa, the Flightcom 403
> intercom installation has begun to
> exhibit a highly irritating background hum with headsets attached and
> engine running.
>
> The hum frequency follows the engine RPM closely. Pulling every circuit
> breaker in the panel, bar the intercom
> itself does not alleviate the problem.
>
> Turning down the individual headset earpiece volume controls helps, but
> does not cure the problem.
>
> Both headsets suffer equally, irrespective of which whether pilot or
> passenger circuit is connected. Disconnecting
> either has no effect. In all other respects the installation behaves as
> it should. (transceiver etc)
>
> Having pulled the panel several times and checked for obviously loose
> wiring, I'm becoming a tad frustrated.
>
> This is clearly leakage and is related to engine turn rate.
>
> Any panel wizards out there got it figured ? Please help. I'm getting
> p...ed off !!
>
> Alan
Have you got an electrolytic capacitor on the output of your alternator? If
so, it might need replacing. They can dry out, especially when used in
somewhere hot.
If not, try adding one. Europa sell a 22000uF one which is probably a bit
overkill, anything over about 4700uF will probably be enough. Use one of at
least 25V. If you have several, you can put them in parallel to add their
values and make a larger combined capacitance. It might also be worth
adding a 0.1uF polyester capacitor at the same point (in parallel with the
electrolytic) and at the point where the supply goes into any box of
avionics.
Maybe worth checking for bad earths and earth loops, which were mentioned a
few weeks back.
Cheers,
Mark.
________________________________
Mark Jackson - +44 (0)7050 645590
europa-builder@ntlworld.com
http://harley.pcl.ox.ac.uk/~mark/Europa
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