DX9/AR9020 system issue?
 

After several years of trouble free flying with my DX9 I had a problem with the DX9/AR9020 installation in an EDF airplane this past Friday. The airplane had 3 previous flights and extensive bench and ground testing. It is set up with two aileron channels and two flap channels so I am using all 9 channels. Since setup, there have been no bind issues with this installation. Range check is also good. To my knowledge there are no RFI issues at our field that might affect 2.4 Ghz.

After a normal power up sequence, I started a control check. When I moved the stick to check the aileron function, the right aileron (connected to the aileron channel) began to oscillate between full up and full down without stopping at midpoint, etc. The servo seemed to be running at full servo speed. It was not "jittering" but driving up/down/up/down, etc. All other control functions, including the left aileron were normal. I unplugged all power in the airplane and turned off the transmitter. Leaving the transmitter off, I plugged the RX power back in but did not power up the ESC/EDF unit. The servo oscillation started again, on the right aileron. All other control functions remained still. (All servos in this airplane are analog with 3 flights on them.)

I have seen some peculiar equipment problems before but this is a new one. The receiver, servos, and electric retracts are powered by a 2S 2200 mah Lipo through a 10A Castle BEC. The BEC voltage regulation is set to 5.5V. Since the problem with the right aileron servo persisted with nothing powered up but the receiver and servos, I assumed there must be a problem with the servo. (Battery is nearly new and was fully charged when this happened.)

At home I powered up the airplane the next day to check it again. The problem did not show up, even with transmitter on and fan running. I ran all kinds of control checks, etc. for a couple of hours. Still not trusting the servo, I replaced it with a new one, then proceeded to bench test it for several hours with another receiver and transmitter. No problem.

A "phantom" problem like this bothers me, especially with a custom built scale EDF airplane that I have a lot of time invested in. Sufficient to say, every connection has been re-inspected and the system is working normally. Now I am beginning to wonder if it is possible the AR9020 could have been driving the servo? We had a "solid" problem/failure at the field, but cannot reproduce it in the shop.

Has anyone else seen this particular problem?

If it happens again I would look at the servo monitor first, that will rule out if its coming from the radio or its isolated to the airplane.

It's sure sounding like a power issue, why run the voltage at 5.5? I'm ALWAYS leary of BEC's that are not switching and I do not know if this one is but I think it's linear.

That said, after making sure it's not an errant tx signal and you think the battery/BEC are up to snuff, I'd be changing out servo leads especially if they've been there for some time and/or are not gold plated pins with a decent wire size.