TM-5-2330-378-14-P
SEMITRAILER, LOWBED: 40 TON CONSTRUCTION EQUIPMENT TRANSPORTER M870 AND M870A1
TECHNICAL MANUAL; OPERATOR'S, UNIT, DIRECT SUPPORT AND GENERAL SUPPORT MAINTENANCE MANUAL (INCLUDING REPAIR PARTS AND SPECIAL TOOLS LIST)
JUNE 1999
TM-5-2330-378-14-P - Page 98 of 524
TM5-2330-378-14&P
4-14. ELECTRICALTROUBLESHOOTING
(continued).
WARNING
Throughouttroubleshootingof theelectricalsystemor electricalcomponents,be
certainMASTERswitchis setto OFFbetweeneverystepunlessotherwisedirected.
To preventinjuryduetoelectricalshock,removealljewelryandmetalobjectswhen
workingontheelectricalsystem.
c.
The multimeter
is used throughout
electrical troubleshooting.
d.
When performing
a shorts test, make sure all connectors
and/or leads are disconnected
from their
components.
Probe the pins (or sockets) with a multimeter.
This is done by placing the red probe on pin (or
socket) A (or 1) and then placing the blackprobeonthe next pin (orsocket) in alphabetical (ornumerical) order.
Probe every pin (or socket) on the connector or lead with the black probe of the multimeter.
e.
When probing has been completed,
place the red lead on the second pin (or connector) and do the probing
with the black lead in order again. Do this until every pin has been probed with the red lead of the multimeter.
Then place the black lead of the multimeter
on the connector,
and place the red lead on each pin (or socket)
on the connector.
f.
If continuity
is present between any two points, a short exists. Shorts must be repaired in order to continue
any operation.
g.
If instructed in a procedure to skip a pin (or socket) during a shorts test, it is because the pin (or socket) is not
used or is shielded.
h.
When a repair or replacement
of a lead or wiring harness has been done, do the shorts test again to make
sure the problem
has been corrected.
i.
When performing
a continuity check, connect the meter probes to both terminals of the circuit you are testing.
Read the meter and interpretthe
results. A meter reading of 5 ohms or less indicatesthe
circuit has continuity.
A very high orinfinite (-) meter reading indicates the circuit is open. Ifthe meter readingjumps
orflickers,
there
is a loose connection.
j. Checklight bulbs for cracks and discoloration.
Checkthe
continuity of a light bulb by placing one probe of the
meter on the metal button base connection
of the bulb and one probe on the metal side of the base. A meter
reading of 5 ohms or less indicates the circuit has continuity. Avery high or infinite(.)
meter reading indicates
the circuit is open, indicating a defect.
4-10
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