Sharp R-9H56, Service Manual

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R-9H56
16
PROCEDURE
LETTER
COMPONENT TEST
TEST PROCEDURES (CONT'D)
G TEMPERATURE FUSE AND THERMAL CUT-OUT TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the temp. 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: 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
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
J MOTOR WINDING TEST
CARRY OUT 3D CHECKS.