STEC 30 troubleshooting

[SantosDumont]

My STEC 30 decided to stop talking to the HSI yesterday.  It was acting a little strange on the ground during pre-flight.  I put the heading bug left and right to test the roll and then when I put the bug center I could hear and feel the servos still whirring.  Then in the air it decided to roll left when I put the bug center, so I turned it off.  Shot some practice approaches and on the way home tried it again and it still seemed to want to roll left.

This morning I tried to troubleshoot it on the ground and the servos would not roll with the heading bug or in nav mode.  Went up in the air and all modes were basically wings level.  Altitude hold still worked fine.

Frustrating that this is all 3 days before my IR checkride, but I guess I'll just INOP it and hand fly everything.

Anyone know anything about troubleshooting it, or is my best bet to call STEC and find a authorized service center? 

[chrisk]

I don't know about trouble shooting the STEC 30.   I took my check ride without an autopilot (or gps).  I passed, you can too.  That said, I would have really liked having an auto pilot. 

[MIm20c]

Do they allow you to use an AP during the check ride?

Sounds like you isolated the issue with the AP. Does the nav course correction data pass through the HSI or is it direct from the GPS?

[DonMuncy]

It is my understanding that the examiner can ask you to demonstrate any equipment installed in the plane. If you don't want to use something it has to be placarded in-op.

[SantosDumont]

1 hour ago, MIm20c said:

Do they allow you to use an AP during the check ride?

Sounds like you isolated the issue with the AP. Does the nav course correction data pass through the HSI or is it direct from the GPS?

The autopilot flies the needle on the HSI in NAV mode. 

[Marauder]

The autopilot flies the needle on the HSI in NAV mode. 

It sounds like a roll computer issue. I would go through the complete ground test from the STEC POH.


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[SantosDumont]

Hmm from searching STEC roll computer looks like there’s some fuses I can check as well as reseating the roll computer connector. I’ll give it a try in the AM. 

[DanM20C]

I had a 30 that would disconnect randomly or roll left randomly. Over a few months it seemed to get more frequent. The avionics guy I was going to take it to told me to unplug and clean every connector that is going to or from the autopilot. After I did the problem never returned. He saved me a lot of money with that one phone call.

Worth a try. 

Cheers,

Dan

[1964-M20E]

Santos

Make sure that the mode selector knob on the lower left is completely pulled out.  Don't rip it out but gently pull back on it.   It is supposed to spring back but as it gets older that sometimes will stop happening.   I had to have mine repaired and ultimately I had the avionics shop install an external mode select button to minimize the wear.   When the button does not come out to it's normal position it will cause the STEC 30 to do weird things.

I now use the knob only at run up when I am testing the AP to make sure the left right servos are functioning.

[DualRatedFlyer]

6 minutes ago, 1964-M20E said:

Santos

Make sure that the mode selector knob on the lower left is completely pulled out.  Don't rip it out but gently pull back on it.   It is supposed to spring back but as it gets older that sometimes will stop happening.   I had to have mine repaired and ultimately I had the avionics shop install an external mode select button to minimize the wear.   When the button does not come out to it's normal position it will cause the STEC 30 to do weird things.

I now use the knob only at run up when I am testing the AP to make sure the left right servos are functioning.

Have any pictures of this external mode select button?  Would be interested in doing that on mine.  

[1964-M20E]

Just now, DualRatedFlyer said:

Have any pictures of this external mode select button?  Would be interested in doing that on mine.  

It is just a non descriptive black momentary push button located on the main panel.  It makes selecting the mode easier than using the knob on the STEC.  You could locate it on the yoke if you have space.  The wiring diagram for the STEC30 shows which lead to connect it to.  I thought about doing it myself but when I had the IFD540 put in just had the avionics guy do it while he was there.

[SantosDumont]

Ok pretty sure the turn coordinator unit is burned out.  Engaged the autopilot on the ground to troubleshoot it today and the smell of burnt plastic started coming from the panel. Took off the panel cover and it’s definately the TC making the smell. Time for an overhaul I guess. 

[Marauder]

Ok pretty sure the turn coordinator unit is burned out.  Engaged the autopilot on the ground to troubleshoot it today and the smell of burnt plastic started coming from the panel. Took off the panel cover and it’s definately the TC making the smell. Time for an overhaul I guess. 

At least now you know. Report back on the repair costs.


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[SantosDumont]

I called STEC support and the dude that answered the phone said it could be anywhere from $900-$1500 for an overhaul.  He said to take it into a shop to have it looks at though because it could be a surge from the servo burning out a diode in the roll computer. 

I need a TC for my IR checkride though so I’ll probably leave it INOP until after my ride. 

[SantosDumont]

Well passed the checkride and took the plane to the shop.  They said the servo had corrosion which was shorting out the roll computer.  They took both out and sent to STEC for overhaul.  This sounds like it’s gonna be expensive.  Too bad I can’t get a Garmin GFC500 yet...

[1964-M20E]

congrats on passing the check ride.

[SantosDumont]

Finally come back from STEC and getting installed today.  $900 for the roll computer and $1400 for the servo... not super horrible.  I was worried it was gonna be upwards of $5k.  Now hopefully it lasts another 20 years.