Trim and Flap Senor Reading Problem - HELP!

[andrewbutler]

Hooking up my three Ray Allen sensors (Flap, Aileron & Elevator Trim) for the final time. I am having some reading problems when I hook up the elevator tab. Flap and Aileron trim readings are perfect.

Can you please tell me how the EFIS uses the three sensor wires (GRN, ORN and BLU) to get a reading. What is the relationship between the ORN & BLU wires and the GRN signal wire? I spoke to the guys at Ray Allen and they said the resistance of the GRN varies from 0 to 5K Ohms, depending on position. How is this read by the EFIS? Is it the resistance from the GRN to GND? Ray Allen send a constant 1.2v through the ORN & BLU wires. What is the purpose of this? Does the EFIS do the same? If the GRN is used to determine the travel of the tab, what is the relationship between the GRN and the ORN/BLU circuit that determines the position of the tab on the screen, relative to the centre position? Ray Allen said if you flip the ORN/BLU wires, the tab will flip about the centre. Is this the same on the EFIS? How does this work?

Symptoms: When I hook up the elevator trim, the Flap reading goes to the bottom, and the trim reading goes to the bottom left of the cross. When I press the elevator trim up botton, the flap reading resumes its correct position, trim reading goes back to the centre and up the line to towards the top and moves towards the top. When I let go of the trim up button, both the flap and trim readings go back to the previous incorrect positions. Pressing the Trim down button has no effect. Anyone seen this before? Any quick answers?

My steps to troubleshoot are:
Hook up my (spare) LED sensor and check that the readings directly from the trim tab are good.
Check the wires going into the back of the EFIS are not crossed
Check for shorts between the elevator trim, flap sensor and aileron trim sensors
Anything else I should consider?

[Trevor Conroy]

As per the EFIS Main cable drawing: Pin 2 is trim/flap sensor power which goes to the White/Blue wire. Pin 3 is ground which goes to the White/Orange wire. Pin 35 is the elevator trim sensor input which is the White/Green wire. We output 10volts to the White/Blue wire and then read the voltage back on the White/Green wire. With trim servo movement, you should have a voltage variation of approx 0-10V on the White/Green wire relative to ground.

Your elevator trim position indication portion of the servo could be blown if it was connected improperly. If the white/green wire is connected to Trim Power (pin 2), it can ruin the potentiometer in the servo and cause those indications.

I would disconnect everything, then connect the flap sensor, run the flaps up and down and verify correct indication. Then disconnect the flap sensor and connect aileron trim. Verify its operation and indication. Then disconnect aileron trim and connect the elevator trim and verify operation and indication.