Section 7 - General Electrical Information & Schematics; General; Multimeter Basics; Grounding - JLG 1930ES Service Maintenance Manual

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, tech-
nically qualified guidance should be obtained before proceeding with any maintenance.

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 dia-
grams 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 specifically
designed for this technique, especially on sealed connectors. Whenever possible insert probes into the side of the connec-
tor such that the test also checks both terminals of the connection. It is possible to inspect a connection within a closed con-
nector 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 cor-
rectly. 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 = 1200 
Example: 50 mA = 0.05 A
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SECTION 7 - GENERAL ELECTRICAL INFORMATION & SCHEMATICS
– JLG Lift – 7-1