On Tue, 29 Jul 2003 18:01:01 -0400, "Victor J. Osborne, Jr."
wrote:

I flew my (new to me) '87 A36 Bonanza at night for the first time recently
and discovered a whine when the panel lights where turned on. The flood
light switch / circuit doesn't do it and the rheostat for the panel light
dimmer changes the frequency.

Where do I start with the troubleshooting? I know any component has to be
replaced by an approved shop but I can read a meter. Could it be as simple
as a lose ground?

I'll bet that the Bo uses a Pulse Width Modulator (PWM) style of lamp
dimmer. If the chopping frequency (or harmonics thereof) are between
30 and 10000 Hz, it might be getting into the low level audio.

You have to ask yourself why? Has it always done this? Did some idiot
avionics tech install an intercom/stereo entertainment system and
screw up the audio grounds by grounding the jacks? Do you hear
alternator whine or strobe squeal in the audio?

Ask the previous owner when it started doing it...

MikeM
Skylane '1mm
PAcer '00z