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View Full Version : Lost pitch/roll servos: D-sub vs Servo problem?


Aggie78
05-12-2017, 11:56 AM
Going to the brain trust on a trouble shooting issue.

I have a dual Dynon Skyview system installed, with both pitch and roll autopilot servos.

Last trip, I got a warning message stating both pitch and roll servos were offline. At home, troubleshooting seemed to narrow the issue down to the connection at the D-sub connecting the aircraft wiring harness to the pitch servo. Spraying it with some cleaner and then securely reconnecting the connections and the complete system was restored.

Until just now. Back to square one, and I know the connectors are firmly in contact with each other.

Where's the likelyhood of finding the issue? The D-sub from the wiring harness? The one attached to the servo? Or, could it be the servo itself?

Apparently, the servos are wired in series (power) and when one goes down, it takes the other with it.

I've trouble shot the power supply, and the switch breaker is good.

What's my best chance of finding the problem?

Thanks!

Edited to add: A vigorous "shake" test of the two tightly attached connectors at this point doesn't get the servos back online...

wilddog
05-12-2017, 12:36 PM
My only experience with Dsubs is from wiring my -8 so it might not be worth much. They are easy to work with only if you have the tools. I would take the connection apart and remove the pins. Check all the female pins, they should grip the male pins and if ok then check the crimps. You might try recrimping all of them. If you have enough slack in the wires, you could cut the old pins off and put new ones on in less time. Good luck!

Raymo
05-12-2017, 01:53 PM
If the D-Sub pins are over crimped, the wire may eventually break. Keep in mind that power could be present with a bad ground causing the same symptom. Ring out the wires from end to end and you should easily find the problem.

Also, consider running separate wires from your fuse/circuit breaker to each servo.

vic syracuse
05-12-2017, 03:19 PM
You didn't state if it was during flight or at startup.
If you recently updated the s/w on the Dynon you will have to scan the network. Some people forget to leave the autopilot on when doing that.

If it happened in flight it sounds like power was lost to the servos. Check that first.

Vic

Mich48041
05-12-2017, 03:52 PM
The most likely problem is inside of a D-Sub connector. Take the back shells off and gently tug on each wire, checking for pins and sockets that are not firmly seated or for broken wires.
The servos are actually connected in parallel. The problem is somewhere between the instrument panel and first servo that the wires come to. The problem is not at the farthest servo, (unless a wire is shorted to ground).

wirejock
05-12-2017, 04:18 PM
You mentioned both dropped at the same time. Do you have a Dynon Hub somewhere?

Aggie78
05-12-2017, 05:00 PM
I have a SV Arinc module, if that matters, with 11 different SV items installed.

This issue has occurred twice on ground power up.

Flew it that way for 3 days the first time, got it home, troubleshooting the breaker showed no problems, so I gained access to the pitch servo and pulled the d-sub on it apart. Had to use 2 paper clips to probe for voltage, as my meter did not have small enough ones to go into the holes. Good voltage at that end.

Sprayed the connectors with a quick dry electronics cleaner, put them back together, and it worked. Did the network detect, calibration, and all was OP's normal!

Today, went down and powered it up again, back to square 1! Auto detect/force network load no help. Shaking harness no help. Dead in the water and no AP servos detected.

How does Dynon supply the servos and wiring harnesses? Do the plugs have to be installed on both? Or, is the servo's pre-installed? I'm trying to decide if there's one d-sub "amateur" installed and one "pro" installed and where to dive in first.

Also, I understand the ease of using the d-subs...but issues like this make me leery of them, too. If length of wiring harnesses isn't an issue (both are plenty long enough) why not use a solder joint for the connections like this:

http://www.unicornelex.com/ProductDetails.asp?ProductCode=23-3791&gclid=CjwKEAjwutXIBRDV7-SDvdiNsUoSJACIlTqlEThFs_Ok1z0YgCk5JiHyPd9UZ_TZPpay _vOW2gS5vRoC38Hw_wcB

Very sturdy, robust connector....of course, if you have to take it apart, you destroy it, but if harness length isn't an issue...why not?

Thanks for the add'l guidance!

wirejock
05-12-2017, 06:28 PM
Servos come with no connector. Same for thee servo network cable.

RV7A Flyer
05-12-2017, 08:27 PM
I have a SV Arinc module, if that matters, with 11 different SV items installed.

This issue has occurred twice on ground power up.

Flew it that way for 3 days the first time, got it home, troubleshooting the breaker showed no problems, so I gained access to the pitch servo and pulled the d-sub on it apart. Had to use 2 paper clips to probe for voltage, as my meter did not have small enough ones to go into the holes. Good voltage at that end.

Sprayed the connectors with a quick dry electronics cleaner, put them back together, and it worked. Did the network detect, calibration, and all was OP's normal!

Today, went down and powered it up again, back to square 1! Auto detect/force network load no help. Shaking harness no help. Dead in the water and no AP servos detected.

How does Dynon supply the servos and wiring harnesses? Do the plugs have to be installed on both? Or, is the servo's pre-installed? I'm trying to decide if there's one d-sub "amateur" installed and one "pro" installed and where to dive in first.

Also, I understand the ease of using the d-subs...but issues like this make me leery of them, too. If length of wiring harnesses isn't an issue (both are plenty long enough) why not use a solder joint for the connections like this:

http://www.unicornelex.com/ProductDetails.asp?ProductCode=23-3791&gclid=CjwKEAjwutXIBRDV7-SDvdiNsUoSJACIlTqlEThFs_Ok1z0YgCk5JiHyPd9UZ_TZPpay _vOW2gS5vRoC38Hw_wcB

Very sturdy, robust connector....of course, if you have to take it apart, you destroy it, but if harness length isn't an issue...why not?

Thanks for the add'l guidance!

When you say "ground power up", do you mean on initial Master ON (prior to engine start), or immediately after engine start?

Aggie78
05-12-2017, 09:31 PM
As soon as it was turned on, before engine start...the servos were offline.

I have a separate AP switch/breaker for the AP.

Usually, it takes 30 seconds or so for the system to boot up. Once they go thru their startup, everything looks good.

Not these times.

Servos were offline, never came online. Warning messages never went away.

greghughespdx
05-12-2017, 09:37 PM
Have you gone into setup *again* and scanned for SV network devices? Crazy dumb question I know, but are the servos powered up at the AP switch when you scan? Don't ask me why I ask that question hah. :)

You could start by checking for power and ground continuity at the pins in the DSUB connectors. That's pretty straight forward to start with.

Bad breaker switch? Again, continuity checks in all modes.

John-G
05-13-2017, 07:43 AM
Rob,

My only suggestion for your immediate issue is to verify that the pins in the D-Sub connector associated with the servo motor are not pushing back into the body of the connector. I have seen pins push back if not fully seated in the connector causing intermittent issues.

I do have a suggestion that will make troubleshooting D-Sub connector wiring much easier for you. I'm sure most here would agree the best way to trouble shoot D-Sub wiring issues with a meter is to fabricate a couple of test wires that can be inserted into the connectors as opposed to the use of probes or paperclips.

You can purchase the male and female pins from Stein Air (good to have spares anyway) along with the crimping tool Stein carries for the pins and make up a pair of test wires with both pin genders on them. The test wires really make it super easy to buzz out a circuit being tested without the possibly of damaging the connector pins while testing. Also, having spring clips or alligator clips on the end of the meter's probes to hold the connector pin while testing with the meter frees the hands so the wiring for the circuit being tested can be held and flexed to see if there is a loss of continuity.

It is good to also have the D-Sub pin insertion and removal tool should you discover you have a bad connection at the crimp and need to crimp a replacement pin onto the end of the wire. Here again, Stein Air carries the insertion/removal tool.

Good luck with your troubleshooting,

rv7charlie
05-13-2017, 09:41 AM
+1 to what John said. Dsubs are the best you will get, short of space-certified.

What's common to both? I'd be checking grounds.

Aggie78
05-13-2017, 09:56 AM
I do believe that the problem lies somewhere in one of the two d-subs, and they have the added benefit of being easiest to replace, easiest to access, as well as the highest likelihood of being the source of the problem.

I'm having a friend with the needed equipment come by Monday, and we will cut/strip/re-pin both connectors, connect up, power up, and see what we get.

Good suggestions on having the needed tools/replacement parts on hand for these assemblies, as my aircraft has d-subs "o' plenty" and I'm sure this won't be the only time something like this will happen....so I am getting an order together for "next time".

Stay tuned, thanks again, and I'll report back on Monday with a after-action report.

Rob

Aggie78
05-13-2017, 10:00 AM
+1 to what John said. Dsubs are the best you will get, short of space-certified.

What's common to both? I'd be checking grounds.

Charlie,

Actually, my understanding is power and ground is common to both...they are wired in parallel..

BUT...I'm not the guy that wired this in originally, however and my electrical skills are limited. Up-thread there was the suggestion to run separate power leads for each servo, which is something I'm mulling over doing next annual when I have everything opened up for inspection.

Rob

RV7A Flyer
05-15-2017, 11:14 AM
As soon as it was turned on, before engine start...the servos were offline.

I have a separate AP switch/breaker for the AP.

Usually, it takes 30 seconds or so for the system to boot up. Once they go thru their startup, everything looks good.

Not these times.

Servos were offline, never came online. Warning messages never went away.

FWIW, I've had this happen on occasion as well (maybe 3-4 times in 4+ years). A power cycle (Master) fixed it every time. I've reported it to Dynon.

I think it's a problem of initialization order within the software, rather than a hardware fault. I say that because a) I'm very confident that my wiring is quite good, for a bunch of reasons not necessary here, b) it affects sometimes one, sometimes the other, sometimes both servos, c) a power cycle clears it (and the plane hasn't changed "state" in any other way), d) it never happens in flight, only on initial start, and e) it's not intermittent or even random...it's a rare event.

Unless it happens a lot on your system, you may wish to simply report it to Dynon (maybe send them a diagnostic logfile as well), and live with the need on rare events to power cycle to clear it. Annoying, yes, but less so than chasing something that isn't there with your wiring.

Aggie78
05-15-2017, 03:18 PM
So, we took both d-subs apart, and there were some non-std wiring issues..insulation under the crimped area, for example.

We cut/stripped and re-installed new pins, reassembled the d-subs and hooked it all back up.

Still dead...and I did the Skyview network scan several times to find out if it was talking to the network, and nothing. It still doesn't see the pitch or roll servos.

Checked continuity of the wiring harness ground pin back thru the harness-good.

Checked continuity of the wiring harness power pin back to the switch breaker-good.

12v power at the harness d-sub is good.

Now looking more like potentially a pitch servo problem...so I have pulled it and see nothing externally amiss, but waiting for a callback from Dynon support to see if I can "at home" bench test this thing or if they have other trouble shooting suggestions before sending the servo in for inspection/repair.

Running out of arrows in the quiver to shoot at this thing...

rv7charlie
05-15-2017, 03:38 PM
Did you do all ends? Extremely unlikely that both servos went bad at the same time. That points to the head or connectors at the head (efis).

Aggie78
05-15-2017, 03:42 PM
Just now went and turned the system on to pull the serial number off the ADSB unit thru the software for the rebate program.

Did another "network scan" with the pitch servo OUT and the harness disco'ed/safety-tied out of the way and it SEES the roll servo now.

This answers a question I had about the system installed in my aircraft.

Apparently, each servo IS individually wired for power and ground and not in parallel as I had originally thought, so that's a good thing.

It also tells me the roll servo is probably ok.

Finally, the pitch servo (or it's electronics) is becoming a prime suspect in that for some reason it's interrupting the comm link between the 2 units on the Skyview Network.

Still waiting to talk to the Dynon folks to run all this past them.

Aggie78
05-15-2017, 04:48 PM
They suggested since the system is now seeing the roll servo, if it's possible, gain access to the roll servo connector, disco it and connect up the wiring harness of the pitch servo to it.

If it wakes up out on the wing, I've probably got a wiring issue to the pitch servo somewhere...if it's still dead, that will pretty much seal the deal its the pitch servo.

Rolling into this project later tonight and will update when I have something to report.

Raymo
05-15-2017, 05:20 PM
My roll servo went out prior to first flight and I had to do the same thing. I rang out the wires and knew they were good but Dynon wanted me to do the swap.

To make things easier, I made another servo harness so I could just plug the pitch servo wiring into the roll servo. Same problem so it went in for repair and came back working like new.

Aggie78
05-15-2017, 09:33 PM
Like a failed pitch servo I could point at and go "A ha!" to.

Not to be.

Moving the pitch servo over the roll servo and hooking it up there and the pitch servo worked like a champ.

So...Not a servo issue, it's an accursed, mundane wiring issue. Bah!!

Tomorrow I do the deep dive behind/under the panel to find the offending connector/wire harness on that end.

Hopefully, it will just be the connector and not a cut wire under the floor somewhere.

Posting all of this for future Dynon troubleshooters....

Logan
07-01-2018, 10:20 AM
Hi, Rob. Did you find a bad connection to this issue? I am facing same issue.

I had to swap pins in the Molex that powered the pitch servo and pitch trim to fix a reverse pitch trim issue. When I plugged it back in, I lost both AP servos. I am sure I must have messed something up in the molex, as it was the ONLY think I touched, but can't for the life of me get it back to working. Hoping for a new aha moment for something else to look at.

Thanks,
Logan

Logan
07-01-2018, 03:29 PM
Duh. Circuit breaker had tripped. As I am using a electronic circuit breaker system, I had to check the right page on the EFIS to see and reset it.

Posting to remind myself and others to start with simple checks first! :)