SECTION 7 - GENERAL ELECTRICAL INFORMATION & SCHEMATICS
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SECTION 7. GENERAL ELECTRICAL INFORMATION & SCHEMATICS
7.1
GENERAL
This section contains general electrical information and
schematics to be used for locating and correcting most
of the operating problems which may develop. If a prob-
lem should develop which is not presented in this sec-
tion or which is not corrected by listed corrective
actions, technically qualified guidance should be
obtained before proceeding with any maintenance.
IT IS A GOOD PRACTICE TO AVOID PRESSURE-WASHING ELECTRICAL/
ELECTRONIC COMPONENTS. SHOULD PRESSURE-WASHING BE UTI-
LIZED TO WASH AREAS CONTAINING ELECTRICAL/ELECTRONIC COM-
PONENTS, JLG INDUSTRIES, INC. RECO MMENDS A MAXIMUM
PRESSURE OF 750 PSI (52 BAR) AT A MINIMUM DISTANCE OF 12
INCHES (30.5 CM) AWAY FROM THESE COMPONENTS. IF ELECTRICAL/
ELECTRONIC COMPONENTS ARE SPRAYED, SPRAYING MUST NOT BE
DIRECT AND BE FOR BRIEF TIME PERIODS TO AVOID HEAVY SATURA-
TION.
7.2
MULTIMETER BASICS
A wide variety of multimeters or Volt Ohm Meters
(VOM) can be used for troubleshooting your equip-
ment. A digital meter with reasonable accuracy (within
7%) is recommended for the measurements in these
procedures. This section shows diagrams of a common,
digital VOM configured for several different circuit mea-
surements. Instructions for your VOM may vary. Please
consult the meter operator’s manual for more informa-
tion.
Grounding
“Grounding the meter” means to take the black lead
(which is connected to the COM (common) or negative
port) and touch it to a good path to the negative side of
the Voltage source.
Backprobing
To "backprobe" means to take the measurement by
accessing a connector’s contact on the same side as the
wires, the back of the connector. Readings can be done
while maintaining circuit continuity this way. If the con-
nector is the sealed type, great care must be taken to
avoid damaging the seal around the wire. It is best to
use probes or probe tips specifically designed for this
technique, especially on sealed connectors. Whenever
possible insert probes into the side of the connector
such that the test also checks both terminals of the con-
nection. It is possible to inspect a connection within a
closed connector by backprobing both sides of a con-
nector terminal and measuring resistance. Do this after
giving each wire a gentle pull to ensure the wires are
still attached to the contact and contacts are seated in
the connector.
Min/Max
Use of the "Min/Max" recording feature of some meters
can help when taking measurements of intermittent
conditions while alone. For example, you can read the
voltage applied to a solenoid when it is only operational
while a switch, far from the solenoid and meter, is held
down.
Polarity
Finding a negative Voltage or current reading when
expecting a positive reading frequently means the leads
are reversed. Check what reading is expected, the loca-
tion of the signal and that the leads are connected to
the device under test correctly. Also check that the lead
on the "COM" port goes to the ground or negative side
of the signal and the lead on the other port goes to the
positive side of the signal.
Scale
M = Mega = 1,000,000 * (Displayed Number)
k = kilo = 1,000 * (Displayed Number)
m = mili = (Displayed Number) / 1,000
μ = micro = (Displayed Number) / 1,000,000
Example: 1.2 kΩ = 1200 Ω
Example: 50 mA = 0.05 A
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