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18
If incorrect readings are obtained, replace the thermal cut-out.
An open circuit thermal cut-out (MG) TC1 indicates that the magnetron has overheated, this may be
due to resistricted ventilation, cooling fan failure.
An open circuit thermal cut-out (OVEN) TC2 indicates that the oven cavity has overheated, this may
be due to no load operation or fire in the oven cavity.
CARRY OUT 4R CHECKS.
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 below.
Table: Thermal Cut-out Test
Temperature of "ON"
Temperature of "OFF"
Indication of ohmmeter
Parts Name
condition (closed circuit).
condition (open circuit). (When room temperature
(
˚
C)
(
˚
C)
is approx. 20
˚
C.)
Thermal cut-out TC1 125
˚
C
This is not resetable
Above 125
˚
C
Closed circuit
Thermal cut-out TC2 145
˚
C
Below 115
˚
C.
Above 145
˚
C
Closed circuit
CARRY OUT 3D CHECKS.
A. Isolate the high voltage capacitor from the circuit.
B. Continuity check must be carried out with measuring instrument which is set to the highest
resistance range.
C. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10M
Ω
after it has been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 M
Ω
because of its internal 10M
Ω
resistance.
F. When the internal wire is opened in the high voltage capacitor shows an infinite resistance.
G. The resistance across all the terminals and the chassis must be infinite when the capacitor is
normal.
If incorrect reading are obtained, the high voltage capacitor must be replaced.
CARRY OUT 4R CHECKS.
E
SWITCH TEST
Table: Terminal Connection of Switch
Plunger Operation
COM to NO
COM to NC
Released
Open circuit
Short circuit
Depressed
Short circuit
Open circuit
COM; Common terminal,
NO;
Normally open terminal
NC;
Normally close terminal
If incorrect readings are obtained, replace the switch.
CARRY OUT 4R CHECKS.
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in
the following table.
F
THERMISTOR TEST
CARRY OUT 3D CHECKS.
Disconnect theconnector B from CPU unit. Measure the resistance of the thermistor with an ohmmeter.
Connect the ohmmeter leads to Pin No's C1 and C3 of the thermistor harness.
Room Temperature
Resistance
20
˚
C - 30
˚
C
Approximately 359.9 k
Ω
- 152 k
Ω
If the meter does not indiicate above resistance, replace the thermistor.
CARRY OUT 4R CHECKS.
D
HIGH VOLTAGE CAPACITOR TEST
PROCEDURE
LETTER
COMPONENT TEST
G
THERMAL CUT-OUT TEST
TEST PROCEDURES
