GPSS - STEC ST-901 vs Garmin G5

teejayevans said:
Yes, I had 901 before G5 upgrade, it works well.
Caveat: 901 must be configured by factory for specific HSI, make sure you get one that matches what you have. It’s stamped on the box, ask for picture to be sure.
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if I only have a DG I won't have that issue, I assume?
 
The mystery deepens. My STEC 30 was sent back to be reconfigured but it was already configured correctly. My shop is rechecking everything but so far has not figured it out. They've always done great work with avionics in the past. I am told it turns at only about half rate and turns faster in one direction than the other. Something is amiss. :(

Before: Mechanical DG, GTN750, ST-901 GPSS, S-TEC 30 (all working perfectly)

Now: G5 AI & HSI, GTN750, GAD29B, S-TEC 30 (only half rate turns, faster in one direction, GPSS not working)
 
I also want to switch to a G5 that will be connected to a STEC 60-2 autopilot.

I wonder if anyone managed to configure it to correctly turn and not hunt while on GPSS...
 
They tried a different GAD29B and a different STEC-30 with the same results. I think they have swapped the two G5 positions too. Everyone is just at a loss. Servos are good, voltage is good. Something has to be misconfigured. :(
 
DesertNomad said:
They tried a different GAD29B and a different STEC-30 with the same results. I think they have swapped the two G5 positions too. Everyone is just at a loss. Servos are good, voltage is good. Something has to be misconfigured. :(
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Is the shop you’re using an Stec dealer?
 
I'm sure they will get it figured out. Google "stec configuration resistors" there are a lotta hits but little useful data.
 
Just got off the phone with the shop who flew it again today. If you start out in HDG mode, it will follow the bug for a while with good turns, but after a few minutes it basically stops working. During this initial time when it is working, putting it in GPSS mode results in it not following a course and then going back to HDG mode results in it still not working.

Cycling the power while in flight does not fix it. They have to land and shut down for a while before it will work again. The G5 indicates a good heading so I think the GMU11 is working.

And yes, the shop is flying the plane... every time they make a change they have to fly it.

They have tried two different G5s acting as an HSI, two different GAD29Bs and two different STEC-30s (both of which were reconfigured to KCS-55 by the same STEC dealer). The wiring shows good continuity. Keep in mind that I am 400 miles away so I can't go look at it. I'm pretty convinced it really needs another set of eyes at this point.

Sigh.
 
Given that my airplane is currently in the shop to have a G5 HSI fitted, that will drive my STEC-30 (which currently has the STEC GPSS module)...I am worried about this! Keep us updated...
 
Are you removing the STEC GPSS in favor of the built in GPSS in the G5?
 
I suggest that you determine if there is a STEC autopilot pin that sets the unit to be in DG mode or HSI mode. It should be in HSI mode. Looking at Garmins install diagram I suspect STEC30 P1 pins 20 and/or 21 are set incorrectly. Find out if those 2 pins are for setting the autopilot to HSI mode. The install diagrams should differentiate between starting with a DG or HSI, but it does not.

When I went from a DG to a G5 HSI my Century21 autopilot would not track the heading bug anymore. I looked at the interface to the C21 and saw that there was a C21 pin that is for configuring the autopilot to be in DG mode or HSI mode. As soon as I changed this C21 pin config (removed ground connected to pin) to HSI mode everthing worked perfect. The Garmin G5 HSI installation diagram was incorrect for my C21 autopilot and did not call out this pin setting correctly. Finding the C21 maintenance manual online was a big help to resolve this issue so I knew which pin to set.

Funny thing is that I told my shop what I thought the problem was and then they tried many other things with no luck. After they spent half a day box swapping, they tried what I suggested and bingo! All it took was removing the ground jumper from the C21 harness.

Hope this helps!
 
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STEC says the AP is configured correctly for a G5, but I'll forward your post to my shop. It's certainly possible the G5 install manual is wrong or misleading.

The G5 manual says GAD29B pins 8/14 go to STEC30 pins 8/7.

I found this STEC manual online and in section 6, page 6-3 for a KCS-55 (which is what the STEC30 has to be configured as for a G5), it shows pins 8/7 but also that pin 35 is involved.

http://www.aeroelectric.com/Installatio ... Manual.pdf

Thoughts?
 
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DesertNomad said:
Are you removing the STEC GPSS in favor of the built in GPSS in the G5?
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After reading your posts I asked about leaving the STEC GPSS. They said that it didn't really make sense, but they'd leave the old GPSS in the panel for an easy switch back if we have issues - but it sounds like it might be more involved than that if the STEC needs to be reconfigured depending on input (G5 vs other DG).

I'm just going to leave it to them for now, haven't used them before but they seem a very competent shop!
 
When something like this happens, who pays the labor for the learning curve?
 
Heftiger said:
When something like this happens, who pays the labor for the learning curve?
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I have already paid for the equipment and have a written quote for the install of the G5s, GMU11, GAD29B and reconfiguration of the STEC-30. The quoted amount is what I plan to pay.
 
DesertNomad said:
I have already paid for the equipment and have a written quote for the install of the G5s, GMU11, GAD29B and reconfiguration of the STEC-30. The quoted amount is what I plan to pay.
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If not they would have told you. This happened on a avionics upgrade, my rack was like Swiss cheese, they called and said they have to rebuild it and it would cost extra.
 
DesertNomad said:
STEC says the AP is configured correctly for a G5, but I'll forward your post to my shop. It's certainly possible the G5 install manual is wrong or misleading.

The G5 manual says GAD29B pins 8/14 go to STEC30 pins 8/7.

I found this STEC manual online and in section 6, page 6-3 for a KCS-55 (which is what the STEC30 has to be configured as for a G5), it shows pins 8/7 but also that pin 35 is involved.

http://www.aeroelectric.com/Installatio ... Manual.pdf

Thoughts?
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The connection on P1 pins 8 and 7 looks correct to me.

See note #3 on page 7-3 of your stec30 manual for pins 20 and 21. It says to remove the jumper between the pins for a DG which is your old set-up. I believe that with the HSI you need the jumper between pins 20 and 21. My guess is that the Garmin install diagram is incorrect on just the DG/HSI config piece.

I am not bashing Garmin. They make terrific products, but have many integrations to define and can make mistakes like anyone. Good luck. BTW I was an Avionics Systems Integration engineer for years until I transitioned into IT work.
 
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The STEC install manual says "remove jumper across pins 20 and 21 of the turn coordinator computer when optional directional gyro or a heading system in being installed".

Garmin's G5 manual says "Remove all jumpers for no heading system."

While the STEC is clear, the Garmin is not. Does it mean "remove all jumpers if you don't have a heading system"? But you do have a heading system since you have a G5. I think what Garmin is saying is remove the "no heading system" jumper.

My installer says there is no jumper and that the heading bug would not work at all with that jumper in place. My heading bug works for about 2 minutes, before stopping completely.
 
The confusion is around what is a "heading system". I think that an HSI is not a directional gyro or a heading system, it is an HSI with different electrical functionality that a DG does not have. The autopilot config should align with an HSI interface so there must be a config pin somewhere. I believe that with the HSI you need the jumper between pins 20 and 21. Its really a small test.

When my autopilot was still incorrectly in DG mode, any GTN flight plan impacted the G5 heading bug (non functional) because it was be impacted by the course arrow signal. Flight plans should not impact your heading bug at all. You can test this when sitting in your airplane. If it does this, then surely try the jumper.

I test my heading bug on the ground with the autopilot "on" and in "Heading" mode. On your G5 in "Heading mode" you should be able to make the yoke turn left or right of current heading with the knob. Flight plan course changes should not impact the heading bug when doing this test. Be prepared to shut the autopilot off if needed. (Note that your AI doesn't need to be driven as long as it is not indicating a turn.)

You will like the G5 once it is set up correctly. Love that it comes with GPSS.
 
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That's a possibility. Garmin seems to think it is a bad G5 so we'll see what happens. This is very frustrating.... I want my plane back.
 
I thought it was the G5 at first as well. I had to start digging through the documents just like you are doing. Try that easy ground test with flight plans changes.

Even though I really liked the work of my avionics installers, I could tell they did not know how to do a quick ground test of the of the GTN to G5 to Autopilot interface using the heading bug and GPSS as described above. No need for a flight test until it passes the ground test.
 
And more data...

1. Replaced the cable between GAD29B and STEC 30.
2. Put the autopilot in heading mode. Got 12 volts to left and right as expected.

Then it gets weird...

With a GPS position (GTN750), put the G5 in GPSS mode with a course between two points which was not over the airport. The course indicator slewed to the desired course and showed a deviation. Measured 20 volts going into the autopilot from the GAD29B. Then put a new course with a different path and the course indicator correctly slewed... again got 20 volts for full turn. This was measured with two voltmeters.

Put the AP back in heading mode and to the right there were 16 volts and to the left only 4 volts with heading bug full left. All this happened with two GAD29Bs. The voltage was piggy backed at the GAD 29B. My installer also removed the plug from the STEC 30 and measured at the STEC 30 plug. I think we have run the course with GAD29Bs as all three have reacted similarly.

We're replacing both G5s.

How is it possible to measure 20 volts on a 12/14 volts system?
 
DesertNomad said:
And more data...

1. Replaced the cable between GAD29B and STEC 30.
2. Put the autopilot in heading mode. Got 12 volts to left and right as expected.

Then it gets weird...

With a GPS position (GTN750), put the G5 in GPSS mode with a course between two points which was not over the airport. The course indicator slewed to the desired course and showed a deviation. Measured 20 volts going into the autopilot from the GAD29B. Then put a new course with a different path and the course indicator correctly slewed... again got 20 volts for full turn. This was measured with two voltmeters.

Put the AP back in heading mode and to the right there were 16 volts and to the left only 4 volts with heading bug full left. All this happened with two GAD29Bs. The voltage was piggy backed at the GAD 29B. My installer also removed the plug from the STEC 30 and measured at the STEC 30 plug. I think we have run the course with GAD29Bs as all three have reacted similarly.

We're replacing both G5s.

How is it possible to measure 20 volts on a 12/14 volts system?
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These are the values inside the G5 software for every preset in it with an earlier software version. It is possible to set each value manually. Why the shop is getting the results they are is beyond me.

upload_2018-12-11_13-29-14.png
upload_2018-12-11_13-29-31.png
upload_2018-12-11_13-29-49.png
upload_2018-12-11_13-30-7.png
 
Looking at the chart BNT83 posted it almost looks like the measurements are off by a factor of 100. Maybe they had the meter on the wrong setting. If you divide their reads by 100 it looks like it makes sense?
 
Also, look at the difference between the heading and course voltage outputs. I can see how if they’re configured improperly one might get “half rate” turns. If it’s sending a “full scale deflection” voltage of .2 when the autopilot is expecting .5 as full scale...
 
Why does the STEC-30 even list a course voltage input since it has only heading input?
 
They have now replaced both G5s and the wiring to the GAD29B and it is still acting the same. :(

Garmin has seen our wiring diagram and says it is correct as are the settings in the G5 configuration.

They have a Comanche in the shop with the same setup as mine (STEC-30, dual G5s, GAD29B, 750). A different avionics guy has been doing that install and it should be ready to fly tomorrow. If it works correctly, then they have something to compare mine to. If it behaves the same, then there is some common problem in the configuration.

They have done other similar installs with an STEC-50, but mine and the Comanche are the first with STEC-30s.
 
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DesertNomad said:
They have now replaced both G5s and the wiring to the GAD29B and it is still acting the same. :(

Garmin has seen our wiring diagram and says it is correct as are the settings in the G5 configuration.

They have a Comanche in the shop with the same setup as mine (STEC-30, dual G5s, GAD29B, 750). A different avionics guy has been doing that install and it should be ready to fly tomorrow. If it works correctly, then they have something to compare mine to. If it behaves the same, then there is some common problem in the configuration.

They have done other similar installs with an STEC-50, but mine and the Comanche are the first with STEC-30s.
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Get a loaner Stec 30 head from the mothership?
 
:eek::confused2:

I can't wait to find out the result. It's better than a mystery thriller.

When do they fly the Comanche?
 
Hopefully tomorrow (Thursday). They tried the S-TEC 30 from the Comanche in mine and there were no changes. Hopefully when the Comanche flies it works and they can do side-by-side comparisons of all the Garmin configs. If it behaves like mine, I will be tearing my hair out.
 
Albert Einstein is broadly credited with exclaiming “The definition of insanity is doing the same thing over and over again, but expecting different results”
 
Good luck finding the problem. I know it is fustraiting. Did the the Comanche start with a DG or HSI before the G5 HSI?
 
I'm not sure what the Comanche started with but different avionics guys are working on each plane so hopefully this will reveal where something was overlooked.
 
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