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Thread: Erratic readings - heat issue?

  1. #1

    Erratic readings - heat issue?

    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

  2. #2
    Does this problem occur with engine running or even with engine off? If the engine is running, have you tried shutting off the alternator? If the engine is not running, are you on a ground power source? If so, what happens running on aircraft battery alone with the ground power source disconnected?

    Please email sys and data logs to support@advanced-flight-systems.com

    CHECK--> MAINT--> ADMIN--> DATA LOGS / SYS LOGS --> START. Files will be on SD card when transfer is complete.

  3. #3
    Quote Originally Posted by Jonathon View Post
    Does this problem occur with engine running or even with engine off? If the engine is running, have you tried shutting off the alternator? If the engine is not running, are you on a ground power source? If so, what happens running on aircraft battery alone with the ground power source disconnected?

    Please email sys and data logs to support@advanced-flight-systems.com

    CHECK--> MAINT--> ADMIN--> DATA LOGS / SYS LOGS --> START. Files will be on SD card when transfer is complete.
    Jonathon, thanks for the speedy reply. I will capture the sys/data logs soon and email them to you.

    The problem occurs both with the engine running and engine off (just the panel powered).
    With the engine running, yes I have shut off the alternator - no affect other than voltage dropping from 14.5 to ~13. Erratic readings will commence (or continue).
    Without the engine running, I have powered the panel many times with just the ship's battery (~12.5V) and many times with the ship's battery on a charger (13-13.5); no difference. Either way the erratic behavior begins sometime after 5 minutes (colder seems to equate to longer, up to 40 minutes).

    Once I accidentally left the master switch on overnight (with a trickle charger which couldn't keep up). The next morning I expected erratic readings - but no, readings were steady and accurate! Voltage was down to around 11.7 so this made me think the 'cut-off' voltage for this behavior is somewhere in the upper 11s. (assuming voltage is the factor causing the problem...). -KJ

  4. #4
    Roger. We should probably get the EFIS shipped back. Just because we didn't find a problem on first blush doesn't mean it isn't there. But do send the logs still, would be good to get a look at those first.

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