Avionics powered up, no smoke! But...

John Courte · #1 09-20-2011, 07:05 PM

I can hear my relays clicking in the headset. I have one set in the floor operating the flaps and trim, and another one on the subpanel activating the starter solenoid. All the avionics (430W, GMA340, GTX327, odyssey) are all grounded on a common forest of tabs attached at the firewall.

In addition to this, when I key the mic, the MGL Odyssey EFIS goes slightly crazy, showing me a 1500fpm descent and a 30 degree yaw until I let go.

What am I missing? Other than a low skill level in avionics installation...

pilot2512 · #2 09-20-2011, 08:47 PM

I'm going to say to look at your com coax and ant very carefully for your second problem.

Jay

Trevor778 · #3 09-20-2011, 08:50 PM

check your audio shields are connected at the audio panel only

Walt · #4 09-20-2011, 09:05 PM

Do you have spike supression diodes on the relays?

John Courte · #5 09-20-2011, 09:43 PM

I do not have spike suppression diodes on my relays. I've not heard of them before. Where should those be wired in? On the power lead on the hi-current side, the driven loads?

My antenna cable is RG400, and I'm pretty sure I did those right, but I don't know. What does a messed up crimp-on BNC connection look like? Would a less than optimal ground plane connection at the antenna mount be a possible culprit?

All my audio shields are definitely all grounded to the frame of the audio panel, per installation manual.

My antenna is mounted just forward of the main spar, as far outboard as I could put it, and which puts it about 2.5 feet directly below the EFIS.

Toobuilder · #6 09-21-2011, 06:48 AM

Did you ohm out your coax cables after the crimps to make sure the center conductor was still isolated from the shielding, and also that your shielding had continuity from one end to the other?

Walt · #7 09-21-2011, 06:48 AM

Quote:

Originally Posted by John Courte

I do not have spike suppression diodes on my relays. I've not heard of them before. Where should those be wired in? On the power lead on the hi-current side, the driven loads?

All relays/solenoids/contactors should have a diode installed, the same as on your master and start contactor. LINK

John Courte · #8 09-21-2011, 10:55 AM

well, I found one possible factor for the antenna issue. On one end of the cable, the pin isn't all the way flush with the plastic end of the BNC connector, which might contribute to a weaker signal and more RF radiating from the cable. The coax ohms out fine when tested, though.

I will have to revisit some of the wiring of sensor packages and the backup battery on the EFIS, I think, and definitely install the spike diodes on all relays.

Thanks for your advice.