Sharp R-872M Service Manual page 13

TEST PROCEDURES
PROCEDURE
LETTER
E SWITCH TEST
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in
the following table.
Plunger Operation
Released
Depressed
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
F THERMISTOR TEST
CARRY OUT 3D CHECKS.
Disconnect theconnector B from CPU unit. Measure the resistance of the thermistor with an ohmmeter.
Connect the ohmmeter leads to Pin No's C1 and C3 of the thermistor harness.
If the meter does not indiicate above resistance, replace the thermistor.
CARRY OUT 4R CHECKS.
G THERMAL CUT-OUT TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the thermal cut-out. Then using an ohmmeter, make a
continuity test across the two terminals as described in the below.
Parts Name
Thermal cut-out 125˚C
Thermal cut-out 150˚C
If incorrect readings are obtained, replace the thermal cut-out.
An open circuit thermal cut-out (MG) indicates that the magnetron has overheated, this may be due to
resistricted ventilation, cooling fan failure.
An open circuit thermal cut-out (OVEN) indicates that the oven cavity has overheated, this may be due
to no load operation.
CARRY OUT 4R CHECKS.
H MOTOR WINDING TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two
terminals as described in the table below.
If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS.
Table: Terminal Connection of Switch
COM to NO
Open circuit
Short circuit
Room Temperature
20˚C - 30˚C
Temperature of "ON"
condition (closed circuit).
(˚C)
This is not resetable
Below 130˚C.
Table: Resistance of Motor
Motors
Fan motor
Turntable motor
Convection fan motor
R-872M - 13
COMPONENT TEST
COM to NC
COM; Common terminal,
Short circuit
NO;
Open circuit
NC;
Resistance
Approximately 359.9 kΩ - 152 kΩ
Table: Thermal Cut-out Test
Temperature of "OFF"
condition (open circuit). (When room temperature
(˚C)
Above 125˚C
Above 150˚C
Resistance
Approximately
Approximately
Approximately
Normally open terminal
Normally close terminal
Indication of ohmmeter
is approx. 20˚C.)
Closed circuit
Closed circuit
293 Ω
15 kΩ
288 Ω