Sharp R-4A68, Service Manual

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R-4A68
11
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER
COMPONENT TEST
.Table: Thermal cut-out Test
Temperature of "ON" condition Temperature of "OFF" condition Indication ofohmmeter
Parts Name (closed circuit) (˚C) (open circuit) (˚C) (When room temperature
is approx. 20˚C)
Thermal cut-out 145˚C This is not resetable type. Above 145˚C Closed circuit.
Temperature fuse 150˚C This is not resetable type. Above 150˚C Closed circuit.
If incorrect readings are obtained, replace the temperature fuse or thermal cut-out.
An open circuit temperature fuse 150˚C (MG) indicates that the magnetron has overheated, this may be
due to restricted 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.
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 295
Ω
Turntable motor Approximately 12.2 k
Ω
If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS.
I BLOWN FUSE 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 1st. latch switch, 2nd. interlock relay
control switch, 2nd. interlock relay, monitor switch and monitor resistor.
If the fuse M8A is blown by incorrect door switching replace the defective switch(s) and the fuse M8A.
CARRY OUT 4R CHECKS.
CAUTION: ONLY REPLACE FUSE M8A WITH THE CORRECT VALUE REPLACEMENT.
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.
1. Key Unit Note : Check key unit ribbon connection before replacement.
The following symptoms indicate a defective key unit. Replace the key unit.
a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.
2. Control Panel
The following symptoms indicate a defective control unit. Before replacing the control unit,