Model 9600/9700 Swing-Reach ® Lift Truck
Section 5. Troubleshooting Electrical Troubleshooting
3. Observe the following measurements: DC Motor Load Handler
Steer
Probe Points
Resistance
LHM-A1 to LHM-S1
<1 ohm
LHM-A1 or LHM-S1 to Frame
>100,000 ohms
MSA1 to MSA2
<1 ohm
MSA1 or MSA2 to Frame
>100,000 ohms
4. If the meter indicates high resistance in the armature, check the condition of the brushes before replacing the motor. 5. If you find an open circuit in a series-wound motor, the motor must be disassembled by a motor rebuilding facility to isolate the problem to the field or armature circuit.
Grounded Motor Test In a grounded motor, an electrical circuit exists between the current-carrying conductors and the motor housing. This can be caused either by direct contact or through conductive foreign material. The ground may be caused by: •
insulation breakdown
•
brush leads touching the motor housing
•
build-up of carbon dust or other materials
Isolate the motor from the lift truck circuit by removing the power cables. Use two wrenches to avoid twisting the terminal studs.
Short Circuited Armature or Field Winding A short circuited winding is one that the insulation on the field or armature has broken down at two or more points. The breakdown creates a low resistance path, allowing current to flow from one turn of the coil to another adjacent coil turn, without actually flowing through the coil wire. The result is a decrease in total resistance of the motor winding and an increase in the current flow. The severity of the short circuit depends on its location. A shorted motor may be indicated by: •
Slow or sluggish operation
•
Running faster than usual (suggests a short in the field)
•
Overheating
•
Blowing a power fuse
•
Burning of brush wires
•
Severe burning or discoloration on armature coil
•
Severe burning or discoloration on one or two commutator segments every 90° of rotation.
These symptoms can be caused by problems other than the motor itself, such as binding in a related pump, hose, or solenoid valve. Testing a motor for short circuited windings requires special equipment at a motor rebuilding facility.
Attach one lead of a megohm meter or a digital ohmmeter to a motor terminal and the other lead to an unpainted surface of the motor housing. Set the ohmmeter to the highest scale. If the ohmmeter reads resistance of <100,000 ohms, the motor is grounded. Clean, repair, or replace the motor as necessary.
Publication: 1089040, Issued: 08 Apr 2016
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