Sharp R-8470, Service Manual

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3. Water container should be one (1) litre beaker made of Pyrex glass and its diameter approxi-
mately cm.
4. Room temperature should be around 20
5. Power supply voltage should be specification voltage.
DISCHARGE THE HIGH VOLTAGE BEFORE TOUCHING ANY OVEN COMPO-
NENTS OR WIRING.
Disconnect the primary input terminals and measure the resistance of the transformer with an
ohmmeter. Check for continuity of the coils with an ohmmeter. On the R x 1 scale, the resistance
of the primary coil should be less than 1 ohm and the resistance of the high voltage coil should
be approximately 73 ohms; the resistance of the filament coil should be less than 1 ohm.
(HIGH VOLTAGES ARE PRESENT TO HIGH VOLTAGE TERMINAL, SO DO NOT ATTEMPT TO
MEASURE THE FILAMENT AND HIGH VOLTAGE.)
C
DISCHARGE THE HIGH VOLTAGE CAPACITOR BEFORE TOUCHING ANY OVEN COMPO-
NENTS OR WIRING.
Isolate the rectifier from the circuit. Using the highest ohm scale of the meter, read the resistance
across the terminals and observe, reverse the leads to the rectifier terminals and observe meter
reading. If a short is indicated in both directions, or if an infinite resistance is read in both di-
rections, the rectifier is orobablv defective and should be replaced.
DISCHARGE THE HIGH VOLTAGE CAPACITOR BEFORE TOUCHING ANY OVEN COMPO-
NENTS OR WIRING.
If the capacitor is open, no high voltage will be available to the magnetron. Disconnect input
leads and check for short or open, between the terminals using an ohmmeter.
Checking with a high ohm scale, if the high voltage capacitor is normal, the meter will indicate
continuity for a short time and should indicate an open circuit once the capacitor is charged. If
the above is not the case, check the capacitor with the ohmmeter to see if it is short circuited
between the terminals. If it is short circuited, replace the capacitor.
Isolate the switch and check the connection by using the ohmmeter accord ing to the following
table.
If improper operation is indicated, make the necessary switch adjustment or replacement.
Table: Switch Connection
Connection Common Terminal-Normally Open Terminal
Common Terminal-Normally Close Terminal
Operation
Open circuit Close circuit Plunger released
Plunger pushed
Closed circuit
Open circuit
Before performing this test, make sure that the upper latch switch is operating properly referring
to the above Switch Test Procedure.
Check the monitor switch operation by using the ohmmeter as following figure.
When the door is open, the meter should indicate a closed circuit.
When the monitor switch lever of the upper latch hook is pushed by a screw driver through the
upper latch hole on the front plate of the oven cavity with the door opened (in this condition the
plunger of the monitor switch is pushed in), the meter should indicate an open circuit.
If improper operation is indicated, replace the defective switch.
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