KJBSouth
Well Known Member
The dream weaver lost its ability to trim left roll. (Stick grip hat switch; Ray Allen 2-10a trim servo; VPX power supply and Garmin GSA28 roll servo) Trim to the right worked just fine. The autopilot had pushed it to the right during the last flight. The fault was found on the ground when I attempted to center the trim.
Day one: I started diagnosing at the wrong spot in the electronic chain. I pulled the seats and floor pans, and removed the Ray Allen only to find that its motor ran well in either direction depending on voltage polarity. I believed the hat switch was working OK as the small trim active light was appearing on the G3X PFD when the switch was pushed either right or left.
Day two: I finally resorted to studying the excellent wiring diagram Stein had supplied with the G3X system. The hat switch grounds a pin on the VPX box which then connects voltage and ground to the Garmin GSA28 sutopilot servo located in the right wing.
The GSA28 is a smart servo. When the autopilot is on, the servo generates it own trim instructions depending on the aileron induced torque at the servo arm. When the autopilot is off, any hat switch/VPS trim signals are passed directly on to the Ray Allen.
Finally enlightened I pulled the wing cover plate and unplugged the DB15 connector from the Garmin servo. I refreshed my memory of connector pin layout and checked for voltage and polarity on the two incoming signal wires. All checked OK. Since there is only one well secured wire pair directly from the Garmin servo to the cockpit and on to the Ray Allen, the fault must be with the Garmin servo.
At this point I brought Stein Air back into the picture. The Garmin servo is beyond warranty. Chris and Nick have arranged an exchange with Garmin at less than half the cost of a new servo, delivered. It should arrive in two days.
I plan on being back in the air this weekend.
Lesson forgotten and relearned: Thoroughly understand the operation of any system before tearing into it for a repair!
Day one: I started diagnosing at the wrong spot in the electronic chain. I pulled the seats and floor pans, and removed the Ray Allen only to find that its motor ran well in either direction depending on voltage polarity. I believed the hat switch was working OK as the small trim active light was appearing on the G3X PFD when the switch was pushed either right or left.
Day two: I finally resorted to studying the excellent wiring diagram Stein had supplied with the G3X system. The hat switch grounds a pin on the VPX box which then connects voltage and ground to the Garmin GSA28 sutopilot servo located in the right wing.
The GSA28 is a smart servo. When the autopilot is on, the servo generates it own trim instructions depending on the aileron induced torque at the servo arm. When the autopilot is off, any hat switch/VPS trim signals are passed directly on to the Ray Allen.
Finally enlightened I pulled the wing cover plate and unplugged the DB15 connector from the Garmin servo. I refreshed my memory of connector pin layout and checked for voltage and polarity on the two incoming signal wires. All checked OK. Since there is only one well secured wire pair directly from the Garmin servo to the cockpit and on to the Ray Allen, the fault must be with the Garmin servo.
At this point I brought Stein Air back into the picture. The Garmin servo is beyond warranty. Chris and Nick have arranged an exchange with Garmin at less than half the cost of a new servo, delivered. It should arrive in two days.
I plan on being back in the air this weekend.
Lesson forgotten and relearned: Thoroughly understand the operation of any system before tearing into it for a repair!
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