Sharp R-933 Service Manual page 18

PROCEDURE
LETTER
THE MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT LEAST 6 VOLTS, BE-
CAUSE OTHERWISE AN INFINITE RESISTANCE MIGHT BE SHOWN IN BOTH DIREC-
TIONS.
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 10MΩ
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 MΩ because of its internal 10MΩ
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.
Plunger Operation
Released
Depressed
If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.
CARRY OUT 4R CHECKS.
F THERMISTOR TEST
CARRY OUT 3D CHECKS.
Disconnect theconnector B from CPU unit. Measure the resistance of the thermistor with an ohmmeter.
Connect the ohmmeter leads to Pin No's C1 and C3 of the thermistor harness.
If the meter does not indiicate above resistance, replace the thermistor.
CARRY OUT 4R CHECKS.
G 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 below.
Parts Name
Thermal cut-out TC1 125˚C
Thermal cut-out TC2 170˚C
Thermal cut-out TC3 170˚C
If incorrect readings are obtained, replace the thermal cut-out.
TEST PROCEDURES
Table: Terminal Connection of Switch
COM to NO
Open circuit
Short circuit
Room Temperature
20˚C - 30˚C
Temperature of "ON"
condition (closed circuit).
(˚C)
This is not resetable
Below 155˚C.
Below 155˚C.
COMPONENT TEST
COM to NC
COM; Common terminal,
Short circuit NO;
Open circuit NC;
Resistance
Approximately 359.9 kΩ - 152 kΩ
Table: Thermal Cut-out Test
Temperature of "OFF"
condition (open circuit). (When room temperature
(˚C)
Above 125˚C
Above 170˚C
Above 170˚C
16
Normally open terminal
Normally close terminal
Indication of ohmmeter
is approx. 20˚C.)
Closed circuit
Closed circuit
Closed circuit