R-950A
15
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
H
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)
Thermal cut-out 170˚C
Below 155˚C
Above 170˚C
Closed circuit.
Temp. fuse 150˚C
This is not resetable type.
Above 150 ˚C
Closed circuit
Thermal cut-out 125˚C
This is not resetable type.
Above 125˚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 thermal cut-out 170˚C (CONV.) indicates that the convection motor has over heated,
this may be due to locked convection fan or cooling fan.
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 125˚C (GRILL) indicates that the outer case cabinet has overheated,
this may be due to resistricted ventilation or cooling fan failure.
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 cool completely.
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 as described in the following table.
Table: Resistance of heater
Parts name
Resistance
Convection heater
Approximately 32
Ω
Grill heater
Approximately 24
Ω
x 2 = 48
Ω
2. Insulation resistance
Disconnect the wire leads to the heater to be tested. Check the insulation resistance between the
heater terminal and cavity using a 500V - 100 M
Ω
insulation tester. The insulation resistance
should be more than 10M
Ω
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.
I
CONVECTION HEATER AND GRILL 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.
J
THERMISTOR TEST
