Sharp R-21AT Service Manual page 11

PROCEDURE
LETTER
it has been charged.
D. A short-circuited capacitor shows continuity all the time.
E. An open capacitor constantly shows a resistance about 10 MΩ because of its internal 10MΩ
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
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in
the following table.
Plunger Operation
Released
Depressed
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
F 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 below.
Parts Name
Thermal cut-out 125˚C
Thermal cut-out 145˚C
If incorrect readings are obtained, replace the thermal cut-out.
An open circuit thermal cut-out (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 (OVEN) indicates that the food in the oven cavity may catch fire, this
may be due to over heating produced by improper setting of the cooking timer or failure of the control
panel.
CARRY OUT 4R CHECKS.
G BLOWN FUSE M10A
CARRY OUT 3D CHECKS.
If the fuse M10A is blown when the door is opened, check the 1st. interlock switch, monitor switch and
monitor resistor.
If the fuse M10A is blown, there could be a short or ground in electrical parts or wire harness. Check
them and replace the defective parts or repair the wire harness.
CARRY OUT 4R CHECKS.
CAUTION:
TEST PROCEDURES
Table: Terminal Connection of Switch
COM to NO
Open circuit
Short circuit
Temperature of "ON"
condition (closed circuit).
(˚C)
This is not resetable type.
This is not resetable type.
Only replace fuse M10A with the correct value replacement.
COMPONENT TEST
COM; Common terminal,
COM to NC
NO;
Short circuit
NC;
Open circuit
Table: Thermal Cut-out Test
Temperature of "OFF"
condition (open circuit).
(˚C)
Above 125˚C
Above 145˚C
9
R-21AT
Normally open terminal
Normally close terminal
Indication of ohmmeter
(When room temperature
is approx. 20˚C.)
Closed circuit
Closed circuit