R-884 (serv.man3) - Sharp Home Appliance Service Manual (repair manual). Page 14

R-884M - 14

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.

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.

Table: Terminal Connection of Switch

Plunger Operation

COM to NO

COM to NC

Released

Open circuit

Short circuit

Depressed

Short circuit

Open circuit

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.

CARRY OUT 3D CHECKS.
Disconnect the connector 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 k

Ω - 152 kΩ

If the meter does not indicate above resistance, replace the thermistor.

CARRY OUT 4R CHECKS.

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: Resistance of Motor

Motors

Resistance

Fan motor

Approximately

293 

Ω

Turntable motor

Approximately

15 k

Ω

Convection fan motor

Approximately

295 

Ω