Sharp R-4A56, Service Manual

Page: 14 / 40

R-4A56
12
PROCEDURE
LETTER
COMPONENT TEST
TEST PROCEDURES (CONT'D)
G MONITOR RESISTOR TEST
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.
H TEMPERATURE FUSE OR THERMAL CUT-OUT TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the temperature fuse or thermal cut-out. Then using an
ohmmeter, make a continuity test across the two terminals as described in the table below.
CARRY OUT 4R CHECKS
.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 -20˚C 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.
I MOTOR WINDING TEST
Table: Resistance of Motor
Motors Resistance
Fan motor Approximately 295
Ω
Turntable motor Approximately 12.5 k
Ω
If incorrect readings are obtained, replace the motor.
CARRY OUT 4R CHECKS.
LIVE TEST FOR MOTOR WINDINGS
CAUTION: THE FOLLOWING PROCEDURE REQUIRES THE OVEN TO BE CONNECTED TO THE
SUPPLY AND SHOULD ONLY BE USED IF THE RELEVANT “COLD” CHECKS FOR THE
MOTOR UNDER TEST ARE INCONCLUSIVE.
1. CARRY OUT 3D CHECKS.
2. Disconnect the leads from the primary of the power transformer. Make sure that the leads remain
isolated from other oven components and chassis. (Use insulation tape if necessary.)
3. Connect a voltmeter, set to 250V AC, across the motor terminals. (Refer to the relevant motor test
procedure or pictorial diagram for the correct terminal numbers.)
4. Arrange the meter in a position where it can be read during the test.
(Do not touch the meter, meter leads or oven circuitry while the oven is active.)