New G-5 HSI and Autopilot Interface Problems

[bucko]

1965 M20-E now with a G-5 HSI (joining a G-5 AI that has been installed for a while) that is having troubles interfacing with the S-Tec 30 autopilot with altitude hold.

In Heading Mode, the plane rocks back and forth, blowing through the desired course by 8 to 15 degrees and then reversing with a hard bank back through the course in the other direction. Was also doing the same thing with GPSS, but decreasing the sensitivity  (to 10 from 100)" fixed" that, sort of.  Have the GAD29b installed.

Avionics shop has cleaned contacts in the autopilot and checked connections to the servos. Autopilot was working fine before the new installation.

 

Any suggestions on getting the airplane to follow HDG and GPSS (without such a low sensitivity setting) without this awful roll.  I have videos that show wings rolling 15 to 25 plus degrees up and down.  It's not a nice ride.

Still waiting to hear from Garmin.

Thanks for any suggestions.

 

Bucko Strehlow

[Andy95W]

Make sure the STEC autopilot has been re-configured to accept the King KCS55 heading protocol.  The “normal” STEC heading input is different, but the G5 outputs the KCS55 instead.  It should be a simple resistor removal, if it is similar to my STEC 50.

[67 m20F chump]

Mine is doing the same thing but I haven’t had time to let the avionics shop look at it.  One guy I talked to thinks the startup voltage of the roll servo is high.  Post if you come up with a solution.  Mine was working fine but started rocking back and forth on a 4 hour flight.

[Jake@BevanAviation]

Start with checking the S-Tec unit strapping for the compass system, it needs to be strapped for a KCS-55A (KI-525A).  If this is not done the system will not work correctly.  After that check servo rigging and start-up voltage.  Ideally the start-up voltage needs to be under 2VDC, the lower the better.

Also, depending on what was removed (DG/HSI) you might want to double check that the unit is still getting the L/R radio error.  The GAD29B only provides the Heading/Course error. L/R radio deviation (analog) has to come from the primary navigator to the S-Tec unit.

[802flyer]

10 hours ago, Andy95W said:

Make sure the STEC autopilot has been re-configured to accept the King KCS55 heading protocol.  The “normal” STEC heading input is different, but the G5 outputs the KCS55 instead.  It should be a simple resistor removal, if it is similar to my STEC 50.

Agree with this. I had to have a new resistor installed in my STEC-30 when I upgraded from a gyro to Aspen.

[Ragsf15e]

I can say that I have the exact same setup and it works perfectly.  Before the g5s, I had a kcs-55a, so I’m thinking mine was already configured for the proper input.