Erratic readings - heat issue? AFS 3400 non-S

I recently acquired an RV-9a project which is ready for first flight except for a puzzling engine monitor issue. When the master switch is turned on, everything displays correctly on the AFS engine page for 5-40 minutes (the time frame seems correlated to ambient temperature). Then suddenly most readings go completely erratic with the values jumping wildly many times per second. The screen becomes very animated with needles, bars, and numbers constantly changing colors and values fluctuating. The only steady and correct values are RPM and Voltage. This eventually occurs on every power-up and will continue until the unit is de-powered and allowed to rest.

But if I remove ship's power (switch to the AFS backup battery, which is lower voltage) the crazy readings will continue for 4-12 minutes and then slowly settle down to normal. At this point all elements of the engine page are valid and correct. I can repeat the cycle by switching between external power and internal backup battery power.

The panel was professionally built by Aerotronics (they built a lot of AFS panels of this vintage) and incorporates an Exp-BUS DC Load Center for power distribution. The continuity of all wires and security of all connectors have been tested. All grounds, including the case ground, have been verified. The behavior occurs even if I unplug both of the sensor connectors on the back of the AFS.

My guess would be something in the AFS unit is overheating with higher voltage. When this first occurred several years ago the unit was shipped to AFS and bench tested (no problems found, but what power supply was used?).

I could likely perform the airworthiness inspection and first flights only using the internal backup power ... but certainly the problem must be solved. Please let me know if you have any troubleshooting ideas, I have exhausted all of mine! Thanks -Kevin


AF-3000 Software Version: 7.5.0-MV15 (Oct 30 2015), Firmware Version: 1.6.6, Unit Serial Number: 60362
All values jump at approx 5 Hz: Fuel Quantity - both tanks, Flap position, Trim position, MAN, Carb Temp, all CHTs/EGTs, Fuel PSI, Oil Temp + PSI, AMP

Kevin Jackson
bossjackson@gmail.com