R-765M (serv.man7). Test procedure - Sharp Home Appliance Service Manual (repair manual). Page 3

R-765M - 12

CARRY OUT 3D CHECKS.

If the special fuse 20A is blown, there will be a short or a ground in either the electrical parts or the wire
harness. Check them and replace the defective parts or repair the wire harness.

CARRY OUT 4R CHECKS.

CARRY OUT 3D CHECKS.

1. If the fuse F8A  is blown when the door is opened, check the monitored latch switch and monitor

switch.

2. If the fuse F8A is blown by incorrect door switching replace the defective switch(es) and the  fuse

F8A.

3. If the fuse F8A is blown, there could be  a short in the asymmetric rectifier or there is a ground in

the wire harness. A short in the asymmetric rectifier may be occurred due to short or ground in H.V.
rectifier, magnetron, high voltage transformer or H.V. wire. Check them and replace the defective
parts or repair the wire harness.

CARRY OUT 4R CHECKS.

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 145˚C

Below 115˚C.

Above 145˚C

Closed circuit

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.

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 or a fault condition within the magnetron or HV circuit.

An open circuit thermal cut-out (OVEN) indicates that the oven cavity has caught fire, this may be due
to over heating produced by improper setting of the cooking time or failure of the control panel.

CARRY OUT 4R CHECKS.