Sharp R-3A56, Service Manual

R-3A56

13

PROCEDURE

LETTER

COMPONENT TEST

TEST PROCEDURES (CONT'D)

 If incorrect readings are obtained, replace the thermal cut-out.

An open circuit thermal cut-out 145˚C (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 145˚C (OVEN) indicates that the foods in the oven may catch fire, this
may  be due to over heating produced by improper setting of the cooking time or failure of the control
panel.

 An open circuit thermal cut-out 95˚C (FAN) indicates that the fan motor winding has overheated, this
may be due to blocked ventilation or locked cooling fan.

CARRY OUT 3D CHECKS.

Disconnect the leads from the monitor resist. Using an ohmmeter and set on a low range. Check between
the terminals of the monitor resistor.

The resistance of monitor resistor is approx.  0.8 ohms.

If incorrect readings are obtained, replace the monitor resistor.

 CARRY OUT 4R CHECKS.

G

MONITOR RESISTOR 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.

H

MOTOR WINDING TEST

Table: Resistance of Motor

Motors

Resistance

Fan motor

Approximately 370 

Ω

Turntable motor

Approximately 16.08 k

Ω

If incorrect readings are obtained, replace the motor.      CARRY OUT 4R CHECKS

J

TOUCH CONTROL PANEL ASSEMBLY TEST

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlike conventional microwave ovens, proper maintenance cannot be performed with only a voltmeter
and ohmmeter. In this service manual, the touch control panel assembly is divided into two units, Control
Unit and Key  Unit, and troubleshooting by replacement is described according to the symptoms
indicated.

I

BLOWN FUSE F M8A

CARRY OUT 3D CHECKS.

1. If the fuse M8A is blown, there could be shorts or ground in electrical parts or wire harness.

Check them and replace the defective parts or repair the wire harness.

2. If the fuse M8A is blown when the door is opened, check the 2nd. latch switch, monitor switch and

monitor resistor.
If the fuse M8A is blown by incorrect door switching replace the defective switch(s) and the fuse M8A.

3. If the fuse M8A is blown, there could be a short in the asymmetric rectifier or there could be a ground

in wire harness. A short in the asymmetric rectifier may have occured due to short or ground in H.V.
rectifier, magnetron, power transformer or H.V. wire. Check them and replace the defective parts or
repair the wire harness.

CARRY OUT 4R CHECKS.

CAUTION: ONLY REPLACE FUSE M8A WITH THE CORRECT VALUE REPLACEMENT