Sharp R-9H56, Service Manual

Page: 17 / 48

R-9H56
15
TEST PROCEDURES (CONT'D)
PROCEDURE
LETTER
COMPONENT TEST
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.
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 circuit
O.C.; Open circuit
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
F BLOWN FUSE F M8A
CARRY OUT 3D CHECKS.
1. If the fuse M8A is blown, there could be shorts or grounds in electrical parts or wire harness. Check
them and replace the defective parts or repair the wire harness.
2. If the fuse M8A is blown when the door is opened, check the upper latch switch, lower latch switch,
monitor switch and monitor resistor.
If the fuse M8A is blown by incorrect door switching, replace the defective switch(s) and the fuse M8A.
3. If the fuse M8A is blown, there could be short in the asymmetric rectifier or there is a ground in wire
harness. A short in the asymmetric rectifier may have occured due to short or ground in H.V. rectifier,
magnetron, power transformer or H.V. wire. Check them and replace the defective parts or repair the
wire harness.
CARRY OUT 4R CHECKS.
CAUTION: Only replace fuse with the correct value replacement.