R-3C57
12
TEST PROCEDURES (CONT'D)
CARRY OUT 4R CHECKS.
ASYMMETRIC RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The asymmetric can be tested using an
ohmmeter set to its highest range across the terminals A+B of the asymmetric rectifier and note the
reading obtained. Reverse the meter leads and note this second reading. If an open circuit is indicated
in both direction then the asymmetric rectifier is good. If an asymmetric rectifier is shorted in either
direction, then the asymmetric rectifier is probably faulty and must be replaced with high voltage rectifier.
When the asymmetric rectifier is defective, check whether magnetron, high voltage rectifier, high voltage
wire or filament winding of the power transformer is shorted.
CARRY OUT 4R CHECKS.
NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF THE
MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BECAUSE
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.
PROCEDURE
LETTER
COMPONENT TEST
A
B
C
D2
D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE RECTIFIER
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 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
CARRY OUT 3D CHECKS.
Isolate the switch to be tested and using an ohmmeter check between the terminals as described in the
following table.
Table: Terminal Connection of Switch
Plunger Operation
COM to NO
COM to NC
Released
O.C.
S.C.
Depressed
S.C.
O.C.
COM; Common terminal,
NO; Normally open terminal
NC; Normally close terminal
S.C.; Short,
O.C.; Open circuit
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
E
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 table below.
CARRY OUT 4R CHECKS
.Table: 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 145˚C
This is not resetable type
Above 145˚C
Closed circuit.
Thermal cut-out 95˚C
Below 75˚C
Above 95˚C
Closed circuit.
