"BRG/NONE" where my heading should be. Autopilot very confused!

[Matt999]

Hi everyone,

I have a dual AF-5500 deck system in my RV-7, and I've been very pleased with it, but after a year of happy flying, it has developed a fault:

When I engaged the AF autopilot recently, the plane veered off the set course, gradually increasing bank angle until I turned the AP off at around 45* bank. The AP seemed to work as expected for the elevator, trying it's best to keep me level. As far as I remember, the AF-Pilot screen appeared as you would expect while this was going on.

The EFIS (PFD and MFD) both appear to be working correctly, but at the top centre of both screens is a message "BRG/NONE" where I would expect the heading (see pic 1).


Background is I bought this RV-7 already built, and noticed a broken wire below the panel. On investigation, I found another unrelated wire also floating in the breeze. I soldered and heat-shrinked where necessary, and removed two wires that didn't go anywhere. To add to my woes, the wiring wasn't documented when the plane was built.

As part of trying to solve this problem myself, I've been going through the manuals, trying to document what I think should be there, and comparing it to what I've actually inspected so far. As part of this process, I've also opened a couple of D-sub connectors and been horrified by what I saw (see pic 2 3 and 4), so intermittent faults may well exist. I'm drawing up a list of D-sub connectors, pins, backshells and wire to replace these soldered horrors. Plus of course a suitable crimp tool.


So back to my "BRG/NONE" issue:
Note both screens are the old OS1 models, so no fancy SV.

Summary info below:

EFIS1 (PFD)
Port 0 AFS AHRS
Port 1 AF-PILOT
Port 2 TRFC/ICARUS (I assume this goes to the Garmin GTX328 transponder)
Port 3 AFS ARINC (71400)
Port 4 GTR/GNC2xx (I have a Garmin GNC255A nav/com fitted)

GPS/NAV1 Remote GPS
GPS/NAV2 Serial port #4
GPS/NAV3 None

Module config:
Engine module HW: off NET: rxd
Air module HW:int NET:txd
AOA module HW:wing NET:txd
AHRS module HW:int NET:txd
XMWX module offline (we don't have XM in Europe)

Diagnostics show activity on ports 0, 1 and 4, but nothing now on ports 2 or 3. Note pic 4 does show ARINC (port 3) as 'alive'.


EFIS2 (MFD)
Port 0 XBOW 525
Port 1 DISABLED
Port 2 GTR/GNC2xx (Garmin GNC255A nav/com)
Port 3 DISABLED
Port 4 NMEA 9600

GPS/NAV1 Serial port #4
GPS/NAV2 Remote NAV
GPS/NAV3 None

Module config:
Engine module HW:int NET: txd
Air module HW: off NET:rxd
AOA module HW:wing NET:txd (same as PFD?)
AHRS module HW: off NET:rxd
XMWX module offline (we don't have XM in Europe)

Diagnostics show activity on port 4, but no others.

The way this plane has been built and wired (eg no 'service loops') makes it tricky to access anything, and I think it not unlikely that by disturbing D-sub connectors, a soldered joint or two may have broken.

I've tried to diagnose this myself, but being new to serial ports and having never heard of ARINC before, I've found it difficult to say the least.

I'm getting to the point of considering how difficult (or expensive!) a complete rewire might be, so if anyone can give me any pointers, I would be extremely grateful!

Kind regards,

Matt
G-RIDG