Autopilot problems and need avionics shop

[jeckford]

I have 2 related issues that I need input on.

 

Recently purchased a well maintainted 1982 M20J and initially the Century 31 autopilot was working perfectly.  There were some pitch related problems with it during the prebuy but this was fixed with overhauling the attitude indicator.

 

Recently it suddenly stopped tracking the HSI (Century360).  It will maintain altitude perfectly and will maintain the heading bug in heading mode but it is tracks 10 degrees to the left in heading mode.

It will not track the CDI.  When the course is put into the G530 and CDI is alligned, the CDI appears to connect appropriately.  When I drift off track the CDI deflects appropriately.  The autopilot does not seem to communicate with the CDI and the heading is all over the place or "wanders"

HSI seems to be slaving appropriately.  Any ideas?

 

2nd question is a good avionics shop in Central Texas to look at this issue.  I am about to fire my current one.  I dropped the plane off Sunday night and they understood that I need the plane this weekend and promised to jump right on it Tuesday.  It is now Wednesday morning and they have not started on it to my knowledge and no one will return my phone calls.  I left 2 messages Monday and 3 message yesterday for the GM.

 

Thanks.

[AndyFromCB]

My problem was identical, however with a King HSI. Take out the HSI and send to Autopilots Central in Oklahoma. My HSI came back working like a charm for about $500 bucks. The needed to replace a photo receptor.

[jetdriven]

take the whole plane to Autopilots Central.  They are good, and will fix it right. FWIW, our Century IIB was gone through by them 8 years ago and it all works great.

[bnicolette]

John,

I also have a 1982 M20J with a Century 31 autopilot and the NSD360A HSI.  My autopilot was doing the same thing.  It would track the heading bug and maintain altitude great.  However, anytime I selected NAV or APR the autopilot would turn right then left and visa versa not tracking the CDI at ALL.  It wandered all over the place with little to no rime or reason.

I called Autopilot Central after a lot of troubleshooting with Century themselves through email.  After a 5 minute phone conversation with Barry at Autopilot Central who had me do some tests while he was on the phone determined the problem.  I removed the HSI and sent it to him for repair.  When I got it back everything is perfect and still is.  This was an ongoing problem with this airplane for years and the seller disclosed this to me before the purchase.  I have multiple receipts where they took it to different shops to get the autopilot fixed with no success.  Barry had the problem dianosed without even seeing a thing!!!

It ended up costing me $2500 to rebuild the HSI but she should be good to go now for many years!  I HOPE!!!!

If you have any questions, please don't hesitate to contact me through PM or my email.

Brett

[bnicolette]

John,

Also, you might want to make sure your heading bug is perfectly aligned under the lubber line before you do anything.  I have heard that if this is off, then everything will be off.  On the control panel of the Century 31 autopilot there are 3 little flat head screws on the very bottom front of the unit.  The one in the middle controls the heading bug and lubber line alignment.  Go flying and make adjustments as neccessary to get them perfectly aligned.  It will take quite a bit of screw turn to move it even 10 degrees.  Don't be afraid to twist the screw.

Also, the screws on the left and right control the amount of bank when turning left and right.  If you turn the heading bug 90 degrees away from your present heading the airplane should not bank more than 24 degrees getting to the new heading.  This is adjusted with the screws on the left and right.  Very easy to adjust these and I would make sure that these parameters are all met before calling Autopilot Central.

If your HSI hasn't been overhauled in a while (mine went close to 20 years before it needed done) then it could quite possibly be the same problem I was having.  However, a call to Barry will solidify your problem.

Let us know how you make out.

[jeckford]

Thanks for the above input guys.  This is why I love this site!

Avionics shop is currently correcting the heading bug and lubber line as they are off 10 degrees.  Hopefully that will fix things.  If not I will investigate getting the HSI rebuilt.

Thanks,

John

[jax88]

I took my Century AP problems to McKee Avionics in San Marcos.  However, I believe most of the repairs were eventually done by Century Flight Systems in Mineral Wells.

[steelerp]

Call Davis Field Aviation located at MKO in Oklahoma.  They have treated me right and never a squak.   http://www.davisfieldaviation.com/    Ask for Nate.     Rick