Sharp R-90GCH Service Manual page 18

R-90GCH
PROCEDURE
LETTER
NOTE: FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE BATTERIES OF
D HIGH VOLTAGE CAPACITOR C1 TEST
1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to "BACK PLATE REMOVAL".
3. Isolate the high voltage capacitor from the circuit.
4. Continuity check must be carried out with measuring instrument which is set to the highest
resistance range.
5. A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10MΩ
after it has been charged.
6. A short-circuited capacitor shows continuity all the time.
7. An open capacitor constantly shows a resistance about 10 MΩ because of its internal 10MΩ
resistance.
8. When the internal wire is opened in the high voltage capacitor, the capacitor shows an infinite
resistance.
9. 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.
10.CARRY OUT 4R CHECKS.
E SWITCH TEST
1. CARRY OUT 3D CHECKS.
2. Isolate the switch to be tested and using an ohmmeter check between the terminals as described
in the following table.
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
3. CARRY OUT 4R CHECKS.
F HIGH VOLTAGE FUSE F3 TEST
1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to "BACK PLATE REMOVAL".
3. If the high voltage fuse F3 is blown, there could be a short in the high voltage rectifier or the
magnetron.
Check them and replace the defective parts and the high voltage fuse F3.
4. CARRY OUT 4R CHECKS.
CAUTION: ONLY REPLACE HIGH VOLTAGE FUSE F3 WITH THE CORRECT VALUE REPLACE-
G NOISE FILTER TEST
1. CARRY OUT 3D CHECKS.
2. Disconnect the leads from the terminals of noise filter.
Using an ohmmeter, check between the terminals as described
in the following table.
MEASURING POINTS
Between N and L
Between terminal N and WHITE
Between terminal L and RED
If incorrect readings are obtained, replace the noise filter unit.
CARRY OUT 4R CHECKS.
TEST PROCEDURES
THE MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BECAUSE
OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIRECTIONS.
Table: Terminal Connection of Switch
Plunger Operation COM to NO
Released Open circuit
Depressed Short circuit
MENT.
COMPONENT TEST
COM to NC
Short circuit
Open circuit
INDICATION OF OHMMETER
Approx. 680 kΩ
Short circuit
Short circuit
16
COM; Common terminal,
NO; Normally open terminal
NC; Normally close terminal
NOISE FILTER
N
NOISE SUPPRESSION COIL
LINE CROSS CAPACITOR 1.0µ/AC275V
RESISTOR 680K 1/2W
RESISTOR
10M
LINE BYPASS LINE BYPASS
CAPACITOR CAPACITOR
0.0047µ/AC250V 0.0047µ/AC250V
WHT
L
1/2W
RED