Posted Tuesday, May 27, 2008 @ 08:55 AM  

In February, I replaced my com & transponder with new Garmin components (SL40 & GTX327). I also replaced the portable intercom I've used with a hardwired intercom.

Since the install, the intercom has never worked right. When you turn on the strobes, the radio would not transmit correctly if the intercom was on. If the intercom was off, the radio worked fine with or without the strobes. Technically, the radio was transmitting a carrier, but the mike seemed disconnected. All you could hear in the was the sound of the strobes charging.

The avionics shop swore it was a radiation interference problem from the older strobe power supply. I got a new one, but it made no difference.

At that point, I started to lose faith in the shop's ability to problem solve.

For the life of me, the issue sounded like a bad wiring/bad ground problem. This weekend, I made a jumper wire so I could connect the strobe power supply directly to the battery. A-ha! No interference problems. I then traced the power supply wires and found that the strobe was grounded to an instrument panel bracket. So...this bracket has one end attached to wood, the other end has a rubber grommet where it attaches to the instrument panel. (Sounds like a great connection to me......NOT)

So, I ran a jumper from the negative side of the battery to the bracket. Again, with the better ground, the radios & intercom worked fine with the strobes on or off. Then I started looking at all the other points behind the instrument panel where people have grounded equipment to assorted brackets, etc., and found many of these points suspicious.

So, I have asked my A&P to run a fresh ground from the main grounding point on the engine to these assorted grounding points just to make sure they really do have a decent ground. (I don't mind doing the trouble shooting, but I'd rather be sure that permanent wiring is done according to standards--hence the A&P.)

(Reminds me of a story about engineers with the first Corvette who couldn't get it to start or any electrics to work -- only to realize they had grounded everything to the body, just they way they had done for years.)

Anyway, it may be worth it to check your grounds with an ohm meter--even as a preventative measure.