Sharp R-7H55, Service Manual

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R-7H55
15
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER
COMPONENT TEST
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 sh ort 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.
G THERMAL CUT-OUT TEST
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 table below.
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.
H MOTOR WINDING TEST
Table: Resistance of Motor
Motors Resistance
Fan motor Approximately 370
Ω
Turntable motor Approximately 12 k
Ω
Convection fan motor Approximately 180
Ω
Damper motor Approximately 11 k
Ω
If incorrect readings are obtained, replace the motor.
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 This is not resetable type Above 145˚C Closed circuit.
Thermal cut-out 150˚C Below130˚C Above 150˚C Closed circuit.
Thermal cut-out 95˚C Below 75˚C Above 95˚C Closed circuit.
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 H.V. circuit.
An open circuit thermal cut-out 150˚C (CONV.) indicates that the convection motor has over heated, this
may be due to convection motor locked..
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.
I CONVECTION HEATER TEST
CARRY OUT 3D CHECKS
Before carring out the following tests make sure the heater is fully cool.
1. Resistance of heater
Disconnect the wire leads to the heater to be tested. Using ohmmeter with low resistance range.
Check the resistance across the terminals of the heater. The resistance of heater is approximately
32 ohms.