Upright AB38, Service & Parts Manual

Page: 44 / 133

Maintenance
Section
4-14 AB38 Work Platform
4.11 Electric Motor (Figure 4-13)
Before carrying out any maintenance
procedures on the electric motor ensure that
the electric circuit is disconnected i.e.
disconnect the batteries and unplug the
charger. It is also important that when dealing
with batteries the proper safety precautions
are adhered to. There is always a hazard of
sparks or explosive gas.
TROUBLESHOOTING
1. Read the nameplate to become familiar with the
motor, especially the rated voltage.
2. Try to turn the shaft by hand. Keep motor leads
separated while doing this.
If the shaft turns
freely go to step 3. If the shaft won’t turn,
proceed to step 2A.
2A. The shaft could be tight for a number of
reasons , this check is to determine if the
tightness is of a temporary nature only. Obtain
power to produce the nameplate voltage. Do
not make a permanent connection.
First touch the motor leads quickly to the power
supply just long enough to observe if the shaft
runs. If it does turn, then hold the motor leads
on the power supply for a longer time. If the
motor sounds normal , go to step 3.
If the motor is noisy it should be taken apart as
described in the
DISASSEMBLY
section.
3. If the motor turned freely, connect an ammeter
in the circuit as shown in Figure 4-12. With
rated voltage applied and the shaft running free,
the ammeter should read less than 20% of the
nameplate full load current. If the motor meets
the above conditions then it can be assumed
that the original problem is external to the
motor.
WARNING
DISASSEMBLY
1. Remove through bolts.
2. Remove pulley end cover
3. Pull the armature out of the assembly in one
swift motion.
4. Remove commutator end cover.
NOTE: Do not place the stator ring in any
mechanical holding device during the
disassembly or assembly operation.
Permanent distortion or other damage will
result.
INSPECTION
Once the motor has been disassembled, go through
the following check list steps to determine where the
problem lies.
1. Bearings should spin smoothly and easily and
have ample lubrication and be free of corrosion.
2. Armature should be checked for grounds and
shorted Windings. Refinish commutator
surface if pitted or excessively worn.
3. Brushes should be checked for wear and to
ensure that they are free in the brush holders.
NOTE: Observe how the brushes are
assembled in brush holders and position of
brush lead. New brushes must be installed in
same manner. Brushes should be removed as
follows:
• Remove brush spring clip from its
mounting on brush assembly.
• Lift brush assembly from the brush holder
• Disconnect brush assembly lead.
• New brush assembly to be installed by
reversing the above procedure.
4. Inspect wire harness and all connections for
signs of damage due to overheating.
5. Check stator to see if it is securely mounted.
CAUTION
REASSEMBLY
1. Install new brushes and be sure they are free in
the holder. Install brush with the lead wires
positioned as when received.
2. Place commutator cover on a work bench with
brush assembly facing upward.
Figure 4-12: Electrical Test Circuit
4.11
AMP METER
A
V
VOLTMETER
D.C.
Power
Supply
D.C.
Motor