That could be caused by a number of factors. Someone else already pointed
out the capacitors going bad with age. I usually try to start with the
least expensive "fixes" and work my way up if the problem persists. The
first thing I'd do in your situation is remove and clean all the connectors
to make sure you aren't getting intermittent connections. I have see the
IIIB do what you described due to a dirty connector on the AI. I've also
seen worn cables so that intermittent shorts were developing. If you can
reach under the panel and affect the autopilot performance by wiggling wires
you should carefully inspect the cabling.

JimC

"Tom Jackson" wrote in message
news:Qexzb.408939$HS4.3307083@attbi_s01...
Jim,
Sounds like you know a thing or two about autopilots.

I have a '74 Warrior, with an Autocontrol IIIB. I find the unit to be
somewhat intermittant at times, when slaved to the heading bug (I don't
have
the piece that ties it into the VOR.)

Sometimes, it holds for a while, then "lets go" and the plane starts a
very
slow circle to the right. If I cycle the autopilot switch on/off several
times, sometimes it starts to hold again (sometimes it doesn't.) It also
seems that the more I use it, the more reliable it gets.

I made a similar post once before, and about the only real comment I
received was someone thinking it may be in the connector on the back of
the
DG.

Would any of these potentiometer adjustments help here (specifically the
one
that has to do with gain/threshold?) Any other ideas?

Thanks



"JimC" wrote in message
...
Jay,

You can adjust the bug centering. I posted a note several months back
(maybe more than a year) regarding the Autocontrol IIIB and its various
adjustments. Do a search on "Autopilot Oscillation Fixed" and you'll
find
the whole posting. I've attached part of the post below covering the
location of the bug centering adjustment potentiometer.

JimC

start
Making the Adjustments:

The adjustments required access to 4 potentiometers located on the
front of the autopilot, behind the faceplate. Removal of the
faceplate required two tools. One Allan wrench to first remove the
roll knob, and a small screwdriver for the faceplate screws. The roll
knob screw is on the bottom of the knob, and the two faceplate screws
are visible after the roll knob is off.

The potentiometers are quite small, arranged horizontally, and are
found directly under the right rocker switch. These pots will not be
visible if you are of normal height and are sitting up in the pilot
seat. A small jeweler-type flat screwdriver is required to adjust
these pots. The pots are 20 turns for full range.

From left to right, the potentiometers adjust the following functions:
gain/threshold, left roll, heading bug centering, right roll.
end


"Jay Honeck" wrote in message
news:dtuzb.213271$Dw6.776220@attbi_s02...
We have the Piper Autocontrol IIIB in our '74 Pathfinder. It has
worked
fairly well since Day One, failing only when our vacuum instruments
each
went Tango Uniform, in the space of six weeks.

However, the "heading bug" on our DG has always off by about 10
degrees.
If
we wanted to fly 180 degrees, we had to set the bug to 170 on the DG.
This
was mildly annoying, but easy to work around.

When the DG died, and we got our newly rebuilt unit (from the Gyro
House),
I
was expecting the heading bug to be PERFECT. Well, imagine my
surprise
when
the NEW heading bug is ALSO off -- by exactly the same amount! We
*still*
have to set the bug on 170 to fly 180!

It's apparent that there is some other adjustment out of whack. But
what?

Even my A&P (who admits he's no autopilot expert) was completely
surprised
that our new DG didn't fix the problem.

What the heck is up? What needs to be adjusted, if not the DG?

Thanks!
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"