mitch(at)skybound.com
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 Posted: Mon Feb 05, 2007 8:19 am Post subject: Garmin 430: Nav 1 audio hum |
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Okay, I'm at whit's end. I've spend the last couple weeks trying to
track down a high pitched "hum" on the NAV 1 audio coming from my new
Garmin 430. I have the Approach Systems Pro-G hub and cable harnesses,
which they just replaced to see if that solves the hum (the hum would
cut in and out when I tugged on the harness so I suspected the
harness). Well, I just spent several more hours installing the new
harness to where I could test it, and the hum is now there all the
time. Wiggling the harness no longer makes the hum cut in and out 
I've done further troubleshooting:
- all Circuit Breaks pulled except NAV (10amp) and COM (5 amp)
- all fuses pulled (everything off except Garmin 430)
- everything in hangar turned off (lights, heaters, etc)
- tried both switching power supply and aircraft battery.
- probed pin 23 on hub AUDIO PANEL HD44, hearing hum
- probed pin 10 on COMM 1 cable going to HD26, hearing hum
- pulled EVERY ground off forest-of-tabs grounding block except battery
contactor, still hearing hum
- swapped Garmin 430's with my hangar mate, still hearing hum.
SO, it seems like the radio is not the problem, and the only thing
between the radio and the headphones is the wire harness! Which is the
second one from Approach Systems, I can't imagine it also has a problem
but you never know. Here's another funny thing, even with all the
grounds pulled off the Garmin 430 it's still running, does it get
grounded through the case and/or plug shields?
P.S. Approach Systems gets an A+++ in my book, they have been extremely
responsive to my emails even on weekends.
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