Sharp R-27STM Service Manual page 9

4. CARRY OUT 4R CHECKS.
C: HIGH VOLTAGE RECTIFIER TEST
CARRY OUT 3D CHECKS.
Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier can be tested using an ohmmeter set to its
highest range. Connect the ohmmeter across the terminal of the high voltage rectifier and note the reading obtained. Reverse the me -
ter leads and note this second reading. The normal resistance is infinite in one direction and more than 100 kW in the other direction.
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 RESIST-
ANCE MIGHT BE SHOWN IN BOTH DIRECTION.
D: HIGH VOLTAGE CAPACITOR TEST
CARRY OUT 3D CHECKS.
1. Isolate the high voltage capacitor from the circuit.
Continuity check must be carried out with measuring instrument which is set to the highest resistance range.
2.
A normal capacitor shows continuity for a short time (kick) and then a resistance of about 10MW after it has been charged.
3.
4. A short -circuited capacitor shows continuity all the time.
5. An open capacitor constantly shows a resistance about 10 MW because of its internal 10MW resistance.
When the internal wire is opened in the high voltage capacitor shows an infinite resistance.
6.
The resistance across all the terminals and the chassis must be infinite when the capacitor is normal.
7.
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.
Plunger Operation Common terminal to Normally open terminal Common terminal to Normally close terminal
Released
Depressed
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
F: TEMPERATURE FUSE TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the terminals of the temperature fuse. Then using an ohmmeter, make a continuity test across the two ter -
minals as described in the below.
Parts Name
Temperature fuse 150°C
If incorrect readings are obtained, replace the temperature fuse.
An open circuit temperature fuse (OVEN) indicates that the food in the oven cavity may catch fire, this may be due to overheating pro -
duced by improper setting of the cooking time or failure of the control panel.
CARRY OUT 4R CHECKS.
G: MOTOR WINDING TEST
CARRY OUT 3D CHECKS.
Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two terminals as described in the table
below.
If incorrect readings are obtained, replace the motor. CARRY OUT 4R CHECKS.
R27STM.indd 9
Table: Terminal Connection of Switch
Open circuit
Short circuit
Table: Temperature Fuse Test
Temperature of "ON" condition
(Closed circuit).
This is not resetable type.
Table: Resistance of Motor
Motors Resistance
Fan motor Approximately 250 W
Approximately 14.7 kW
Turntable motor
Temperature of "OFF" condition
(Open circuit).
Above 150°C
9
Short circuit
Open circuit.
Indication of ohmmeter
(When room temperature is approx. 20°C.)
Closed circuit
R-27STM
11/3/08 2:04:26 PM