Troubleshooting advice for panel mount GPS installation

ChiefPilot · #1 12-23-2010, 05:26 PM

Hi All,

I finished wiring in my King KLN89B GPS and Dynon D10A/EMS-10 over the last couple of days, and both are working great with one exception - the GPS resolver interface.

The GPS thinks the CDI (KI 209A) is always at 15 degrees +/- a degree. Calibrating the unit doesn't help; it just stays at whatever value the calibration value sets it to. I've triple checked the wiring and it matches the King-supplied diagrams. Everything else works correctly; the self-test moves the needle and to/from flag as would be expected.

Can anyone offer any suggestions on where to look next? My guess is that perhaps one of the units are bad but I'd still suspect a wiring issue before a bad unit. The interface is quite simple - only four signals - and as I mentioned I've verified correct continuity several times.

Thanks for any advice anyone might be able to offer!

ChiefPilot · #2 12-26-2010, 09:47 PM

After much investigation and a complete re-do of the harness, I figured out the issue. I thought I'd post the solution here since it may affect anyone using a King KI 208A/209A indicator with any make of GPS.

Although the installation docs for the indicator state that it has two separate power inputs (NAV & GPS) to allow it to be powered by either source, the OBS resolver is in fact powered only by the NAV. This means that while the needle and to/from flags are functional when the indicator is powered by the GPS, power must still be supplied via the NAV power input in order for the resolver to function. Once I figured this out, I reassembled everything and added power to the indicator via the NAV pin and everything worked properly.

No wiring mistakes on my part after all - I thought I had made a mistake somewhere, but it turns out I was mistaken :-). Incidentally, I think stuff like this is why it's worth the $$$ to pay someone like Stein to handle this - if I could have afforded to do so, I certainly would have.

Bob Axsom · #3 12-27-2010, 01:23 AM

I have been flying our RV-6A for close to seven years now and and I have modified the panel several times. If you draw up your schematics/wiring diagrams and design and build you own panel it gives you an intimate familiarity for work that will come up farther down the road.

Bob Axsom

ChiefPilot · #4 12-27-2010, 05:59 AM

Quote:

Originally Posted by Bob Axsom

I have been flying our RV-6A for close to seven years now and and I have modified the panel several times. If you draw up your schematics/wiring diagrams and design and build you own panel it gives you an intimate familiarity for work that will come up farther down the road.

Bob Axsom

Hi Bob,

I completely agree - I have at least one schematic for everything in my aircraft that has electrons flowing through it on a regular basis, and even though I'm not flying yet it has proven to be valuable several times. In fact, this GPS/CDI thing is the first issue I've had where things didn't just work when I applied power. My entire electrical system firewall aft worked the first time without any smoke, and the other avionics I've installed so far (Dynon EFIS, EMS, AP74, pitch & roll servos, PM3000 intercom, Garmin GTX327, Dynon serial-2-gray code convertor, etc.) all worked on the first try. I suspect that I would still be trying to find wiring errors if I didn't have the diagrams (and the hours of thought put into them) to work from. Some people could do it without the diagrams, but unfortunately I'm not nearly that smart :-)

Thanks!
Brad Benson