JLG 3246ES Service Manual - Manual (Page 177)

SECTION 7 - GENERAL ELECTRICAL INFORMATION & SCHEMATICS
3121166 – JLG Lift – 7-1
SECTION 7. GENERAL ELECTRICAL INFORMATION & SCHEMATICS
7.1 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 presented 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 A GOOD PRACTICE TO AVOID PRESSURE-WASHING ELECTRICAL/ELECTRONIC COMPONENTS. 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/ELECTRONIC COMPONENTS ARE
SPRAYED, SPRAYING MUST NOT BE DIRECT AND BE FOR BRIEF TIME PERIODS TO AVOID HEAVY SATURATION.
7.2 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 recommended for the measurements in these procedures. This section
shows diagrams of a common, digital VOM configured for several different circuit measurements. Instructions 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 connector 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 specifi-
cally 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 connection. It is possible to inspect a connection within a
closed connector 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 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 location 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 = milli = (Displayed Number) / 1,000
μ = micro = (Displayed Number) / 1,000,000
Example: 1.2 k
Ω = 1200 Ω
Example: 50 mA = 0.05 A