Electric trim: Request help to diagnose failure

[Riseric]

Searched the forum but didn't find much help. Link me if something is relevant.

Probing the collective minds here for suggestions.

During pre-flight, 19 times out of 20 I check the electric trim's operation.
It always worked.
Last Sunday was one of those, "naw, it worked perfectly last time" skip the trim check moment...
On initial climb, as I had to hold back pressure to keep +/- 100KIAS, I activated the stick's hat-switch for nose up. No Joy.
Levelled off, speed increased, only slight back pressure needed but still no response from the hat-switch.
Tried the rear stick hat-switch, nothing...
Turned the A/P on to see if that could command the trim but no... Message to "Trim Nose UP" of course.
Function of A/P buttons on the SV-AP-PANEL are OK.
Checked the VP-X breaker to the SV-AP-PANEL, was OK, reset anyway (OFF/ON) but no change.

No issues handling the RV, slowed to approach speed, flaps down, flared and landed quite normally, just some extra back pressure needed on the stick. Easily manageable.
Shut down completly, waited a few moments for any magic to happen and restarted all as usual. Still no trim.
Previous flight was with a passenger (RV-8), this one was solo, explaining the more nose down trim on approach, requiring extra back pressure.
Since new, (Nov. 2021, 125 hours) trim operated normally, never an intermittent episode.
Since that last flight, all attemps to operate the trim were negative.

Setup:
Dynon HDX.
SV-AP-PANEL wired for auto-trim. (serial # 6474, not concerned by SB-00090).
VP-X providing power to SV-AP-PANEL.
Ray Allen T3-12A trim servo (2011 - 2012 ish).
Front and rear Infinity Aerospace grip sticks with hat-switches.

Here's a summary of what was checked this past week.

Dynon network check shows all modules "Ready", no fault messages.

Disconnected the 15 pin connector from the SV-AP-PANEL, (wired as per Dynon's instructions).
Measured 13.1 Volts between pins #9(+) and #2 GND.
Applied power from a battery to motor pins #7 & #8 and servo motor responds both ways.
Checked electrical continuity in wires from pins #3, #4, #5, and #6 to their respective ends in both hat-switches.
Checked above 4 wires that they are not grounded except when hat-switches are operated.
Hat switches grounds were checked OK.

To me, all wiring seem sound, tell me if I missed something.

Further, with the system powered and no trim command input, this is what I measured (Volts) on each of the 5 wires running back to the servo:
Between WHT/ORG and any of the 2 (motor) WHT: 4.95
Between WHT/ORG and WHT/BLU (ref): 4.95
Between WHT/ORG and WHT/GRN: (pos) 2.68

Can anyone say if these are desireable values or can anyone measure their values if your similar system is under maintenance or construction??
I will also post this on VAF for support on these findings.

With all this, I'm starting to suspect the SV-AP-PANEL's internal trim circuit board or 15 pin connector.
I would try another module if there was one available for swap on or near my field. Still looking...

Thank you for reading !!

 

[jakej]

FWIW I’d do is try your a/p panel in another plane - NOT a ‘loaner’ in your 8. If there is a problem in your 8 other than the a/p panel it could cause damage to the loaner unit, if your a/p panel does have a fault it will show up in the plane you test it with.

 

[Riseric]

Yes, that would be prudent, thank you for the suggestion.
For now, no immediate or close-by candidates available to test my A/P PANEL in their airplane.
I have a buddy that has a A/P PANEL installed but with manual trim... He's an hour away, flight time.
As I'm pretty confident that all my hard wiring is sound, chances are low that another unit in my plane gets damaged.
In the meantime, on Monday, I'll disable the A/P AUTO-TRIM feature through the SETUP MENU and see if that brings any change.

 

[CanardMulti]

You might try temporarily removing the AP panel from the circuit by simply wiring around it directly to the hat switches, one at a time. If the trim operates normally without the AP panel included, that pretty much narrows it down to either the panel itself or just maybe a pin problem.

Good luck.

 

[jakej]

A while ago, before the SB, I had several customers with issues with the a/p panel. My temp solution to enable them to fly was to make a plate, same size as the panel, & mounted a biased switch on it to just control pitch trim servo (pitch was all they really needed) while the issue was being worked on - simple & no need to mess with anything else

 

[Riseric]

Yes, I thought about wiring a separate circuit to by-pass the a/p panel.
Guess I could temporarily use the 15 pin connector to power a proper relay and connect the servo and pilot switch.
I know that the wiring to the 15 pin connector all checks OK...

 

[jakej]

I have a diagram on how to do that if you want, it uses the same pin numbers as the 15 pin connector ?

 

[Riseric]

Thanks Jake, I'm confident I'll manage. If lost, I'll come back to you.

I ordered a trim relay and it has a pretty straightforward wiring diagram. Should get it in a couple of weeks.
I will disconnect the 15 pin connector and insert D-Sub male pins in it to connect power, servo and hat-switch.
I'm very confident that the wiring to that connector is sound.
That should make the trim function again. If not, I'm in it deep, cause I don't know where else to look...
If it works, that would increase suspicion about the AP-PANEL.

Still looking/asking around to get another plane with similar setup for a test swap.

For those that want to know, I manually adjusted the trim to neutral and test flew this morning.
RV-8. Easy-peasy to handle from stall to 170 Kts. Yes, some pressure is needed other than in level cruise at 150 KTAS.
Very manageable.

 

[CanardMulti]

I have Infinity stick grips in my airplane and had a similar relay board before I installed my AP panel which now serves that function. I agree that a relay board is a good idea for a permanent or even a semi permanent flying installation. That said, know that if all you want to accomplish is testing then the Infinity paperwork notes that the switches are rated for about 6 amps for 12V / 3 amps for 28 volts. See the last bullet point:

 

[Riseric]

OK, thanks for the reminder.
If I read correctly, the Infinity hat-switch can handle up to 6 A.
Knowing that the Ray Allen servo pulls about 800ma, to further test the hat-switches, I could jump connector #9 (+12v) to, say #7 (motor) then jump #3 (pilot up) to #8 (motor).
Nothing should move until I activate the UP trim command on the pilot hat-switch.
# 4, 5 and 6 connectors could be tested the same way, correct ???

Continuities and switch functions were already confirmed.
That test would confirm the confirmation... lol

Next step would be to swap AP-PANELs or contact Dynon support.

 

[CanardMulti]

Sorry, the pin numbers you cite sound like the leads for the Ray Allen trim motor, for which I'm clueless. My trim is via a surplus 24 volt Globe gear motor being run on 12 volts to slow it down.

The attached pictures document which buttons on the stick connect to which wires. The #1 refers to left side stick. Prior to adding my AP panel control of which stick (left or right) commanded the trim was selected by a switch on the panel in order to keep the relay board simple. The autopilot on / disconnect have since been added to button #6. The pins in pencil refer to the pins in the 25 pin Dsub connector I use to connect the lead from the stick to the rest of the plane's inputs.

 

[Riseric]

The connectors #'s I referred to above are those from the 15 pin to the AP-PANEL.
Disconnected, I then have access to 12v power, the servo and both switch wires.

 

[jakej]

Riseric, I’ll pm u a diagram of what i use - is easy to follow & uses the existing 15 pin dsub connector numbers so its a plug & play solution & can be kept for future use if ever needed. No need to mess with anything else, just plug into the a/p panel connector.

 

[jakej]

 

[Riseric]

Thank you Jake for the diagram.

Today I can really confirm that all related wiring from the 15 pin connector to the servo and respective stick switches is sound.
I jumped connector #9 (12v) to #7 (motor)
I jumped connector #3 (pilot nose up) to #8 (motor)
No movement as expected.
Then the Nose Up command was activated and the servo responded.
Same for connectors 4, 5 and 6. (respective commands on both sticks of course).

Seems the culprit is internal to the SV-AP-PANEL or software.
I will get in touch with Dynon support.

Again, thanks to all that replied here.