R-7N76(W)M
R-7N76(B)M
14
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.
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER
COMPONENT TEST
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 or replace the switch.
CARRY OUT 4R CHECKS.
F
MONITOR RESISTOR TEST
CARRY OUT 3D CHECKS
Disconnect the leads from the monitor resistor.
Using an ohmmeter and set on a low range.
Check between the terminals of the monitor resistor as described in the following table.
Table: Resistance
Resistor
Resistance
Monitor resistor
Approx. 0.8
Ω
If incorrect readings are obtained, replace the monitor resistor.
CARRY OUT 4R CHECKS
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
D
HIGH VOLTAGE CAPACITOR TEST
