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HELP!! Autopilot roll servo wiring issue.

B

Blizzard

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First let me start with the fact that the entire aircraft is Garmin. Very near having the airworthiness inspection scheduled. Last thing I did was put the wings on for the last time. First time I actually connected the d-subs to the roll servo and powered everything up. That’s when things went south. Hopefully a Garmin guru out there can enlighten me as to what the problem might be. Here’s an abbreviated list of components I have that would relate to my issue. Dual GDU 460’s PFD and MFD. GMC 305 autopilot controller. Two GSA 28’s and a GTN 650. Been trying to troubleshoot for 3 days and about to give up!

Scenario 1. Hook everything up normally. Turn power on to everything . The two screens start flashing red X’s on just about everything. Engine instruments, Attitude, HSI..etc

Scenario 2. Unplug the roll servo and pull the autopilot circuit breaker. Both GDU’s return to normal and all the information returns to normal. Both screens communicate with each other as normal. Only message I get is ADAHRs not receiving Magnetometer data. Understandable as it’s not calibrated yet.

Scenario 3. Plug the roll servo back in and leave the autopilot CB pulled. Result is see Scenario 1!

Scenario 4. Unplug the roll servo and reset the autopilot CB. Result is see Scenario 1 again!!! ARGH!!

Here’s where I ABOUT LOST IT! Decided to throw the Pitch servo into the mix.

Scenario 5. Disconnected the the pitch servo and attached a Garmin “removed GSA 28 d-sub” to the end that would attach to the servo. Disconnected the roll servo again but left the autopilot CB IN and this time everything worked as it should.

Scenario 6. Left everything as it was in Scenario 5 and plugged in the roll servo again and you guessed it…..SEE SCENARIO 1!!! *#!#!!**##

The wiring harnesses and panel were built by Pacific Coast Avionics. Sean did a spectacular job. Now as a bit of possible screw-ups on my part. I have d-subs at the wing root to the actual servo in the event I ever had to remove the wing I would just have to unplug it instead of de-pinning it. Could the described scenarios above be a result of possibly swapping either the can-bus pins or the RS-232 pins? The common denominator in all this is the roll servo connector at the wing root. The other possible issue could be in the configuration modes for the RS-232 settings for the autopilot. I don’t mind repinning the can-bus pins or the RS-232 pins at the connectors I just want to be sure that screwing with these pins won’t damage anything if they are wrong. (Maybe they already are wrong). My gut tells me this a communication issue between my roll servo and the autopilot and or the rest of the can-bus or RS-232 communication link. Does this sound like a can-bus or RS-232 communication conflict?

Starting to feel like this RV-10 is trying to get in it’s lost shot to the “you know what’s” before it concedes and let’s me win!!! LMAO


Thanks for any input that anyone can provide.
 
Map your can bus out. There should be one path end to end and only the ends should have the 120 ohm can termination resistors. The servos have the ability to be can terminators if you join two pins and there are also the can terminators that go between the dsub and lru.

Also be sure you have the servo id strap correct to differentiate the pitch from roll.

The resistors have effect even if the cbs are pulled. I would start there given your symptoms.
 
how is the canbus looking when you look at the set up screen. are you getting errors.. where are the two terminal ends of the can bus ? if you need a break from troubleshooting take the autopilot out of the equasion and keep moving forward.. you dont need it for the inspection or flyoff.
 
My hangar neighbor had something similar with his -10 with the Garmin Servos, big red X's that would basically cause the whole set-up to go south, only a power reset would solve the issue for a time, then would happen again. He went through everything, tracking canbus voltage/ohms..., terminated the canbus short to see if it was too long, basically ripped his plane apart trying to find the problem....etc....Turns out there was a recall on the servos he installed. New servos fixed the problem as far as I am aware. Apparently its not a well known recall. Food for thought.
 
I’m pretty sure you’ll get a “Magnetometer Not Calibrated” not a not receiving data massage. There was a recall for the servos but that was 4 or 5 years ago but easy to check part number and serial numbers. Garmin will verify.

“Only message I get is ADAHRs not receiving Magnetometer data. Understandable as it’s not calibrated yet.”
 
dmattmul said:
I’m pretty sure you’ll get a “Magnetometer Not Calibrated” not a not receiving data massage. There was a recall for the servos but that was 4 or 5 years ago but easy to check part number and serial numbers. Garmin will verify.

“Only message I get is ADAHRs not receiving Magnetometer data. Understandable as it’s not calibrated yet.”
Click to expand...
The recall is active through May 2028. There are a ton of units affected. If they were purchased more than a year ago I’d double check they weren’t affected.
 
If Pacific Coast Avionics did the harness, did they also perform a power-on check of all components in their shop? I'm guessing they did, and most shops will ensure everything is configured properly and running correctly. If they did, then something got cockeyed when you undid a D-sub to pull the wires through the wing. Frankly, it's easy to mess that up. Been there, done that. Look at any D-sub or connector you took apart and confirm that it's wired properly. Get a magnifying glass if you need to read the tiny numbers.

If the shop didn't run a check before they shipped it, then the field opens up dramatically as to what may be wrong.
 
jacoby said:
The recall is active through May 2028. There are a ton of units affected. If they were purchased more than a year ago I’d double check they weren’t affected.
Click to expand...
The recall was issued May 2023 for 5 years. If yours is older than this MIGHT be an issue. And yes, lots were affected pre-May of 2023.

Garmin GSA 28 Servo Service-Life Extension (Service Bulletin 23038)

Good Morning, We released a Service bulletin today that outlines a Service-Life Extension program for our GSA 28 Autopilot Servos. Garmin has implemented several design and manufacturing process improvements to improve GSA 28 reliability. The latest update has been added to a consolidation of...
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