COMPASS REPAIR PROCEDURES
VARIATION ADJUSTMENT PROCEDURE
Variance is the difference between magnetic North
and geographic North. In some areas the difference
between magnetic and geographic north is great
enough to cause the compass to give false readings. If
this occurs, the variance must be set.
To set the variance:
(1) Turn ignition switch to the ON position.
(2) Depress both buttons and holddown until VAR
light appears. This takes about 5 seconds.
(3) Release both buttons.
(4) Using the map (Fig. 1) find your geographic lo-
cation and note the zone number.
(5) Press the U.S./METRIC button to sequentially
go through the numbers until the zone number for
your area appears in the display.
(6) Press the COMP/TEMP button to enter this
zone number.
(7) Confirm correct directions are indicated.
COMPASS CALIBRATION PROCEDURE
CAUTION: DO NOT use magnetic tools when servic-
ing the overhead console.
CAUTION: DO NOT place any external magnets
such as magnetic roof mount antennas, in the vicin-
ity of the compass.
Do not attempt to set compass near large metal ob-
jects such as other vehicles, large buildings or
bridges. The compass features an ``Auto-Cal'' design
which simplifies the calibration procedure. During
normal driving this feature automatically updates
the compass calibration. This takes into account in-
cremental changes in magnetism the vehicle may see
over its lifetime.
Whenever the compass is calibrated manually,
the variation number must also be reset.
Calibrate the compass as follows:
(1) Start the engine.
(2) Depress both buttons on the compass and hold
down until CAL light appears. This takes about 10
seconds and appears about 5 seconds after the VAR
light appears.
(3) Release buttons.
(4) Drive vehicle on a level surface that is away
from metal objects through three or more complete
Fig. 1 Variance Settings
Chart 3
8C - 4 OVERHEAD CONSOLEJ
circles, in not less than 48 seconds. The CAL light
will go off and the compass is now calibrated.
(5) Reset variation number. This step must be
done every time step 2 is performed.
If CAL light does not go off, either there is ex-
cessive magnetism near the compass or the unit
is defective. Repeat the degaussing and calibra-
tion procedures at least one more time.
If the wrong direction is still indicated, the
area selected may be too close to a magnetic
source. Repeat the calibration procedure in an-
other location.
DEGAUSSING PROCEDURE
The tool used to degauss or demagnetize the forward
console attaching screw and roof panel is the Miller
Tool 6029. Equivalent units must be rated as continu-
ous duty for 110/115 volts, 60Hz with a field strength of
over 350 gauss at 1/4 inch beyond the tip of the probe.
In this degaussing procedure the degaussing tool is
used to demagnetize both the roof panel and console
forward mounting screw.
(1) Be sure the ignition switch is in the OFF posi-
tion before you begin the degaussing procedures.
CAUTION: Keep the degaussing tool at least 2 inches
away from the compass area when plugging it in.
(2) Plug the degaussing tool into a standard
110/115 volt AC outlet.
CONSOLE FORWARD MOUNTING SCREW
(3) Slowly approach the head of the forward
mounting screw with the plastic coated tip of the de-
gaussing tool. Contact the head of the screw for
about two seconds.
(4) With the degaussing tool still energized, slowly
back it away from the screw until the tool is at least
2 inches from the screw head then unplug the tool.
ROOF PANEL
(5) Place an 8 1/2 X 11 piece of paper on the center
of the roof at the windshield, oriented lengthwise
from front to rear. The purpose of the paper is pro-
tect the roof panel from scratches and define the area
to be degaussed (Fig. 2). Figure 2 shows the recom-
mended sweep pattern of 1/2 inch between passes in
a sweeping zig-zag pattern.
(6) Plug in the degaussing tool. Keep the tool at
least 2 inches away from the compass unit.
(7) Slowly approach the center of the roof panel at
the windshield with the degaussing tool plugged in.
(8) Contact the roof panel with the tip of the tool
(be sure template is in place to avoid scratching the
roof panel). Using slow sweeping motions of 1/2 inch
between sweeps, move the tool approximately 49ei-
ther side of the centerline and at least 11 inches
back from the windshield.(9) With the degaussing tool still energized, slowly
back it away from the roof panel until the tip is at
least 2 inches from the roof then unplug the tool.
(10) Calibrate the compass and set the variance as
described.
SELF-DIAGNOSTIC TEST
The self-diagnostic test is used to verify the com-
pass is working properly electrically. This can be
used to confirm that the display and all of its seg-
ments are operating properly. Initiate the self-diag-
nostic test as follows:
(1) With the ignition switch in the OFF position si-
multaneously press and hold the COMP/TEMP but-
ton and the US/METRIC button.
(2) Turn ignition switch to ON.
(3) Continue to hold both buttons until the display
performs a walking segment test. In this test all of
the compass points are displayed along with various
number combinations. These combinations verify
that all segments work. To repeat the test, press the
COMP/TEMP button.
(4) Press the US/METRIC button, and all segments
will light simultaneously for about 2 seconds. To re-
peat the test, press the COMP/TEMP button.
(5) Press the US/METRIC button to return to nor-
mal operation.
Fig. 2 Roof Degaussing Pattern
JOVERHEAD CONSOLE 8C - 5
