
Group 38 Instrumentation, VNL, VNM General
General
General Work Practices
CAUTION
When servicing or troubleshooting, do not leave the
cluster face-down for more than 15 minutes, or
damage to the gauges may occur. Gauge oil may run
out of the front of the gauge faces and make the
gauges inaccurate.
CAUTION
Welding on trucks can damage the vehicle electrical
system/components from the voltage and current
spikes that normally occur when welding. It is prefer-
able to avoid welding on an assembled truck, but if
welding must be done on any structure on or in
contact with the vehicle, disconnect the electrical con-
nectors at the rear of the instrument cluster, all ECU’s
and the battery cables. When disconnecting the bat-
tery cables, disconnect any other ground cables
connected to the battery first, then the main battery
ground. Attach the welder ground cable as close to
the weld as possible.
Preventing electrostatic discharge
(ESD)
CAUTION
To prevent electrostatic discharge (ESD), which may
damage the sensitive electronic components in the in-
strument cluster, a wrist grounding strap must be
used when working on electronic equipment such as
the instrument cluster. Failure to use a wrist strap may
result in permanent damage to the printed circuit
boards in the instrument cluster. To use the wrist strap
in a vehicle, attach the alligator clip to the nearest
electrical ground such as a metal mounting screw, a
ground terminal or preferably a ground stud.
CAUTION
To prevent electrostatic discharge (ESD), which may
damage the sensitive electronic components in the in-
strument cluster, make sure the workbench has an
anti-static mat which is grounded to the nearest elec-
trical outlet when working on the instrument cluster.
Failure to use an anti-static mat may result in perma-
nent damage to the printed circuit boards in the
instrument cluster. When working at the anti-static
workbench, always keep a wrist strap connected to
the anti-static mat.
When dealing with circuits designed to sense differences
smaller than 1 volt, electrostatic discharge can be a sub-
tle but destructive problem. Circuit boards mounted in
the instrument cluster or in modules mounted elsewhere
may not fail immediately after being hit with a static dis-
charge. Rather they may work for a while, then fail for no
apparent reason. The culprit then is often the normal
warming up and cooling down process of the module,
engine or cab interior.
Grounding straps and anti-static mats are available for
minimal cost from electronic supply stores. Grounding
straps consist of a wrist strap, a coiled extension wire
and an alligator clip. Be sure to purchase one with a long
enough extension wire to allow freedom of movement.
Anti-static wrist straps and mats are available from
Kent-Moore (see). Call 1-800-328-6657.
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