Sharp R-9H58, Service Manual

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R-9H58
15
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
CARRY OUT 3D CHECKS.
Disconnect connector-E from the CPU unit. Measure the resistance of the thermistor with an
ohmmeter. Connect the ohmmeter leads to Pin No’s E-3 and E-4 of the thermistor harness.
Room Temp. .................. 20˚C - 30˚C
Resistance ..................... Approx. 350k
Ω
- 155k
Ω
If the meter does not indicate above resistance, replace the thermistor.
CARRY OUT 4R CHECKS.
I THERMISTOR TEST
Table: Temperature Fuse and 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)
Temp. fuse 150˚C This is not resetable type. Above 150 ˚C Closed circuit
Thermal cut-out 150˚C Below 130˚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 temp. fuse or thermal cut-out.;
An open circuit temperature fuse 150˚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 150˚C (OVEN) indicates that the convection motor has over heated,
this may be due to convection motor locked.
An open circuit thermal cut-out 95˚C (FM) indicates that the fan motor winding has overheated, this
may be due to blocked ventilation or locked cooling fan.
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 37.5 ohms.
2. Insulation resistance
Disconnect the wire leads to the heater to be tested. Check the insulation resistance between the
element and cavity using a 500V - 100Mohms insulation tester. The insulation resistance should
be more than 10Mohms in the cold start.
If the results of above test 1 and/or 2 are out of above specifications, the heater is probably faulty
and should be replaced.
CARRY OUT 4R CHECKS.
H CONVECTION HEATER TEST
J MOTOR WINDING 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.
Table: Resistance of Motor
Motors Resistance
Fan motor Approximately 295
Ω
Turntable motor Approximately 10.5 k
Ω
Convection fan motor Approximately 210
Ω
Damper motor Approximately 11 k
Ω