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Thread: AFS 3500 Phase I test issues

  1. #1

    AFS 3500 Phase I test issues

    I am seeing an RPM display that is useable but it oscillates +/- 50 RPM in cruise. I have the constant speed prop set to 2350 confirmed by an optical tach on the glare shield and the RPM display varies between 2300 and 2400 three or four cycles in a 2 minute period.

    Looking at the same 2 minutes of data, EGT and CHT are +/- 5.

    A probably unrelated symptom is, "No GPS". The GPS talks to the Trio autopilot reliably but the AFS only gets the signal once in a while. Strangely, the data file shows Latitude, Longitude, and Ground Speed consistently.

    I am saving the .ALD files for each flight and it is an amazing amount of detail.

    Any help is greatly appreciated.

    John Morgensen
    RV9A

  2. #2
    Make sure your RPM sensor wires are not located with the P Lead wires.
    Rob Hickman
    Advanced Flight Systems Inc.

  3. #3
    My tachometer finally died completely.

    I have tried the LCOM filter, ran a new shielded sensor wire, and re-routed the P Lead wires with no joy. I have learned to live with the oscillation and just ignored it.

    Sunday, on a flight from Phoenix to Reno, the tach stopped working completely. The flight started as usual, but in cruise the tach started jumping around to 3000+ rpm and zero. It stopped at 0 for a while and then decided to show ~550 rpm. Later it hoovered around 300 and finally went to zero and stayed there. Briefly, it showed ~100 rpm and went back to zero.

    The Hobbs flight time for the day shows 2.28 hours - the actual flight time was 3:50. The tach time did not move at all. There was a stead high pitch noise in the intercom that went away when the tach was zero. I have never had noise in the intercom before. I was solo and only listening to the XM radio.

  4. #4
    Advanced Flight Systems Shawn McGinnis's Avatar
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    What pin are you using for your RPM pickup. What type of mag pickup do you have? Have you verified that the sensor is still installed and give a slight tug verify it is solid in its housing.
    Shawn McGinnis

    Advanced Flight Systems
    support@advanced-flight-systems.com

  5. #5

    Tach signal

    Quote Originally Posted by Shawn McGinnis View Post
    What pin are you using for your RPM pickup. What type of mag pickup do you have? Have you verified that the sensor is still installed and give a slight tug verify it is solid in its housing.
    The 3500 serial numbers are 60281 and 60282.

    The installation is dual P-Mags and the sensor is on pin 33. When I was getting ready for the first flight in July of 2013, the Pmags were refreshed to the latest and greatest version and the signal was verified. After talking to Rob, I sent the unit back to you and some hardware magic was performed so that it would read the signal on pin 33 as indicated in the manual. It started giving me a tachometer display that was accurate but it fluctuated +/- 50 rpm around the actual rpm. Rob sent me a document of various fixes for the rpm signal and I installed the LCOM filter, moved the p-leads, tried the sensor from the other p-mag, and installed a shielded sensor wire. None of these attempts had any affect.

    I have lived with this oscillation for almost 2 years but have not found a fix. However, the oscillation is not the current problem. I am grounded with no tachometer, no tach meter, and the hobbs meter is reporting less than actual time.

    I would like to find a fix for the annoying oscillations but my primary concern is getting back in the air.

    What can I do now? Do I need to send the unit in? Is there an add-on board to take a P-Mag signal and process it for pin 32?

    Please help,
    John Morgensen

  6. #6
    Advanced Flight Systems Shawn McGinnis's Avatar
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    Have you ran the lead to the second P-Mag?
    Try removing the additional filter to see if the filter is damaged.
    Remove the signal line and tap it to +12v and see if you get pulses on your EFIS.

    You could switch to the 5v signaling (install diode) and move pin 33 back to pin 32.

    Alternatively, our 71420 RPM Interface board allows for a dual P-Mag installation using Pin 32.
    Shawn McGinnis

    Advanced Flight Systems
    support@advanced-flight-systems.com

  7. #7
    Just a quick update. Adding a ground from the Pmag to the airframe brought back the tach signal but it still oscillates as before. The next step will be to try a 5 volt signal to pin 32. I will report back on this thread.

    john

  8. #8
    Added diode for 5 volt signal and changed input to pin 32. No joy. I am looking for an "Aha" moment where all of the symptoms come together.

    Symptoms in cruise:
    RPM +/- 50
    Noisy EGT and CHT
    Fuel flow +/- .1
    All of the other guages are stable - oil pressure, oil temp, fuel pressure, volts, amps, etc.

    Other anamolies:
    On landing, EGT#3 becomes eratic -1276 to 475 in 30 seconds.

    Looking over the RPM wiring, where should pin 31(White/Orange) and Pin 16(Black) go when using P-Mags?

    john

  9. #9
    Advanced Flight Systems Shawn McGinnis's Avatar
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    Lets start with the EGT / CHT noise. Are the sensors from an upgrade or from AFS? If you disconnect the crimp terminals and measure ohm from each lead to the probe case are you getting any readings below 5MΩ? If they are they probably need to be replaced. Try leaving any out of spec probes disconnected and testing for noise.

    Quote Originally Posted by johninreno View Post
    where should pin 31(White/Orange) and Pin 16(Black) go when using P-Mags?
    Those can be removed or capped off.
    Shawn McGinnis

    Advanced Flight Systems
    support@advanced-flight-systems.com

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