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Old Jan 19, 2013, 12:06 AM
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Canada, ON, Ottawa
Joined Mar 2011
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Throttle servos frying - cause unknown

It appears that I have fried a couple of throttle servos - the one that came with the plane when I bought it, and a spare I used for testing. Here's the background:
  • When I first connected the receiver (Futaba 6000HS) and transmitter (Futaba 8FG), all of the servos were performing properly
  • Over the last couple of days I've done some work with the wiring - rerouting, shortening leads and labeling
  • Today after putting everything back together, the rudder and elevator servos responded but throttle servo (Futabe S3152) did not.
  • I noticed as I advanced the throttle past the halfway point the ignition LED goes out. It comes back on again as the throttle is lowered
  • I plugged the throttle servo into another channel on the receiver but it still did not respond - this is when I suspected it was fried
  • I plugged another servo into the throttle channel (3) to test the receiver and the servo responded. This also leads me to believe the problem is with the throttle servo
  • I plugged a spare servo (JR DS821) into the throttle channel (3) to test it and it worked (at first)
  • A second test of the spare throttle servo saw the servo not responding to transmitter input. However, when the receiver is turned on the throttle servo rotates 1/8 turn counter-clockwise and emits a low-volume, high pitched hum - and it gets hot fast. Thus I suspect this servo is now also fried.
  • The wiring of the ignition cutoff (42 percent products Opto Gas Engine Kill Switch) has been verified as correct
  • The wiring of the voltage regulator (Smart Fly 2S Lithium, 5.2V output) has been verified as correct

Here's the wiring diagram:

The lead between the ignition cutoff and the voltage regulator is especially long. While I was cleaning up the wiring I folded the wire back on itself several times and secured it with a zip tie, like so:

I have no idea if this could be the source of the problem but I have since removed the zip tie and unfolded the wire again.

I bought a new throttle servo but I'm reluctant to try it before I can figure out what the problem is. Help would be much appreciated!
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