JLG M4069 Service Manual - Manual (Page 113)

SECTION 6 - GENERAL ELECTRICAL INFORMATION & SCHEMATICS
3121639 – JLG Lift – 6-1
SECTION 6. GENERAL ELECTRICAL INFORMATION & SCHEMATICS
6.1 GENERAL
This section contains schematics to be used for locating
and correcting most of the operating problems which may
develop. If a problem should develop which is not pre-
sented in this section or which is not corrected by listed
corrective actions, technically qualified guidance should
be obtained before proceeding with any maintenance.
IT IS GOOD PRACTICE TO AVOID PRESSURE-WASHING ELEC-
TRICAL/ELECTRONIC COMPONENTS. IN THE EVENT PRES-
SURE-WASHING THE MACHINE IS NEEDED, ENSURE THE
MACHINE IS SHUT DOWN BEFORE PRESSURE-WASHING.
SHOULD PRESSURE WASHING BE UTILIZED TO WASH AREAS
CONTAINING ELECTRICAL/ELECTRONIC COMPONENTS, JLG
INDUSTRIES, INC. RECOMMENDS A MAXIMUM PRESSURE OF
750 PSI (52 BAR) AT A MINIMUM DISTANCE OF 12 INCHES (30.5
CM) AWAY FROM THESE COMPONENTS. IF ELECTRICAL/ELEC-
TRONIC COMPONENTS ARE SPRAYED, SPRAYING MUST NOT
BE DIRECT AND BE FOR BRIEF TIME PERIODS TO AVOID HEAVY
SATURATION.
6.2 MULTIMETER BASICS
A wide variety of multimeters or Volt Ohm Meters (VOM)
can be used for troubleshooting your equipment. A digital
meter with reasonable accuracy (within 7%) is recom-
mended for the measurements in these procedures. This
section shows diagrams of a common, digital VOM con-
figured for several different circuit measurements. Instruc-
tions for your VOM may vary. Please consult the meter
operator’s manual for more information.
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 connec-
tor 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 tech-
nique, especially on sealed connectors. Whenever possi-
ble insert probes into the side of the connector such that
the test also checks both terminals of the connection. It is
possible to inspect a connection within a closed connec-
tor by backprobing both sides of a connector terminal and
measuring resistance. Do this after giving each wire a
gentle pull to ensure the wires are still attached to the con-
tact 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 condi-
tions 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 sig-
nal 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 = milli = (Displayed Number) / 1,000
μ = micro = (Displayed Number) / 1,000,000
Example: 1.2 kΩ = 1200 Ω
Example: 50 mA = 0.05 A