Sharp R-772WM - Page 13

13
E SWITCH TEST
COM; Common terminal,
NO; Normally open terminal
NC; Normally close terminal
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in
the following table.
F THERMISTOR TEST
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
G THERMAL CUT-OUT TEST
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.
Table: Resistance of Motor
Motors Resistance
Fan motor Approximately 293 Ω
Turntable motor Approximately 15 kΩ
If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS.
Table: Terminal Connection of Switch
Plunger Operation COM to NO COM to NC
Released Open circuit Short circuit
Depressed Short circuit Open circuit
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 below.
Table: Thermal Cut-out Test
Temperature of "ON" Temperature of "OFF" Indication of ohmmeter
Parts Name condition (closed circuit). condition (open circuit). (When room temperature
(˚C) (˚C) is approx. 20˚C.)
Thermal cut-out 125˚C This is not resetable Above 125˚C Closed circuit
Thermal cut-out 150˚C Below 130˚C. Above 150˚C Closed circuit
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
restricted 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.
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.
Room Temperature Resistance
20˚C - 30˚C Approximately 359.9 kΩ - 152 kΩ
If the meter does not indiicate above resistance, replace the thermistor.
CARRY OUT 4R CHECKS.