Sharp R-212B Service Manual page 46

R-212B
PROCEDURE
LETTER
D HIGH VOLTAGE CAPACITOR TEST
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 10MΩ
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 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
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in
the following table.
CARRY OUT 3D CHECKS.
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
F MONITOR RESISTOR TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the monitor resist. Using an ohmmeter and set on a low range. Check
between the terminals of the monitor resistor.
If incorrect readings are obtained, replace the monitor resistor.
CARRY OUT 4R CHECKS.
G TEMPERATURE FUSE OR THERMAL CUT-OUT TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the temperature fuse or the thermal cut-out. Then using
an ohmmeter, make a continuity test across the two terminals as described in the below.
CARRY OUT 4R CHECKS.
Parts Name
Temp. fuse 120˚C
Thermal cut-out 95˚C Below 75˚C
If incorrect readings are obtained, replace the temperature fuse or thermal cut-out.
An open circuit thermal cut-out (MG) indicates that the magnetron has overheated, this may be due
TEST PROCEDURES
Table: Terminal Connection of Switch
Plunger Operation COM to NO
Released O.C.
Depressed S.C.
The resistance of monitor resistor is approx. 0.8 ohms.
Temperature Fuse or Thermal Cut-out Test
Table:
Temperature of "ON" condition
(closed circuit).
This is not resetable type.
COMPONENT TEST
COM to NC
S.C.
O.C.
Temperature of "OFF" condition Indication of ohmmeter (When room
(open circuit).
Above 120˚C
Above 95˚C
10
COM; Common terminal,
NO; Normally open terminal
NC; Normally close terminal
S.C.; Short circuit
O.C.; Open circuit
temperature is approx. 20˚C.)
Closed circuit
Closed circuit.