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Figure 5-18. Motor Input Voltage
NOTE
If the pump has been activated continu-
ously for 1-1/2 to 2 minutes, the thermal
relay will interrupt the power to the
pump.
b. Thermal Protector Test
The Thermal Protector is built in to the pump motor
and is used to interrupt the current flow to the pump
motor to protect it from possible damage due to
overheating.
NOTE
Whenever there are several compo-
nents of the same type, a defective
unit can also be detected by substi-
tuting a known good unit or wire con-
nector. In some cases this may be
faster than using a multi-meter.
5-11. Motor/Pump Assembly
The hydraulic pump motor is a thermally protected
24 volt DC electric motor. The oil pump unit is
attached to the bottom of the motor and is a gear
type displacement pump with a pumping capacity
of .4 liter per min. The Motor/Pump Assembly is
mounted on insulators in the base of the table.
a. Motor/Pump Test
1. Make sure all connectors are connected and
activate the AC120V operating mode. See figure
5-18.
2. Test HN4 at pin 1(+) and pin 2(-) with a DC
voltmeter. Meter should read approximately 24-28
volts when any function button is activated. If no
voltage is present, use an ohmmeter to test the
continuity from HN4 to CN4 (red and black wires).
1. Turn OFF both BATTERY and AC120V
operating modes.
2. Use an ohmmeter to test for continuity
between terminals 3 and 4 on the connector HN4.
See figure 5-19.
Figure 5-19. Thermal Protector
3. The Thermal Relay should reset itself after
approximately one minute.
4. The Thermal Relay should activate after 1-
1/2 to 2 minutes of continuous pump operation.
c. Motor Resistance Test
The motor can be statically checked for resistance
using an ohmmeter. This test is not 100% accurate
because you are checking the motor with very low
voltage from the meter and without any load.
1. Using an ohmmeter R x 1 scale, measure the
resistance between the pins 1 and 2 of HN4. See
figure 5-20.
2. The meter should read 1 to 2 ohms at room
temperature.
3. Measure the resistance between either pin
and ground.
4. Meter should read infinity.
Figure 5-20. Motor Connector HN4
d. Test Results:
If you do not receive the correct meter readings, the
motor or wiring is defective.
HN4
82306-517
1
2
82306.518
HN4
3
4
82306.519
HN4
1
2
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