Sharp R-933 Service Manual page 20

PROCEDURE
LETTER
3. If the fuse F2 F8A is blown, there could be shorts in the asymmetric rectifier or there is a ground
in wire harness. A short in the asymmetric rectifier may be occurred due to short or ground in H.V.
rectifier, magnetron, high voltage transformer or H.V. wire. Check them and replace the defective
parts or repair the wire harness.
CARRY OUT 4R CHECKS.
CAUTION:
L GRILL HEATING ELEMENTS (TOP) AND CONVECTION HEATING ELEMENT TEST
CARRY OUT 3D CHECKS.
Before carrying out the following tests make sure the heating element is cool completely.
1. Resistance of heating element.
Disconnect the wire leads to the heating element to be tested. Using ohmmeter with low resistance
range. Check the resistance across the terminals of the heating element as described in the
following table.
2. Insulation resistance.
Disconnect the wire leads to the heating element to be tested. Check the insulation resistance
between the element terminal and cavity using a 500V - 100MΩ insulation tester. The insulation
resistance should be more than 10 MΩ in the cold start.
If the results of above test 1 and/or 2 are out of above specifications, the heating element is probably
faulty and should be replaced.
CARRY OUT 4R CHECKS.
M CONTROL PANEL ASSEMBLY TEST
The control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore, unlike
conventional microwave ovens, proper maintenance can not be performed with only a voltmeter and
ohmmeter.
In this service manual, the control panel assembly is divided into two units, Control Unit and Jog and
Switch Unit, and also the control unit is divided into two units, CPU unit and Power unit, and
troubleshooting by replacement is described according to the symptoms indicated.
1. Jog and Switch Unit Note : Check Jog and Switch unit wire harness connection before replacement.
The following symptoms indicate a defective Jog and Switch unit. Replace the Jog and Switch unit.
1-1. Tact switch
a) When touching the buttons, a certain button produces no signal at all.
b) When touching the buttons, sometimes a button produces no signal.
1-2. Potentiometer
a) When rotating the potentiometer, the cooking mode can not be selected.
1-3. Encoder
a) When rotating the encoder, the cooking time or the weight of food can not be entered.
2. Control Panel
The following symptoms indicate a defective control unit. Before replacing the control unit.
perform the Jog and Switch unit test (Procedure N) to determine if control unit is faulty.
2-1 In connection with buttons
a) When touching the buttons, a certain group of buttons do not produce a signal.
b) When touching the buttons, no buttons produce a signal.
2-2 In connection with indicators
a) At a certain digit, all or some segments do not light up.
b) At a certain digit, brightness is low.
c) Only one indicator does not light up.
d) The corresponding segments of all digits do not light up; or they continue to light up.
e) Wrong figure appears.
f) A certain group of indicators do not light up.
g) The figure of all digits flicker.
TEST PROCEDURES
Only replace fuse F2 F8A with the correct value replacement.
Table: Resistance of heating element
Parts name
Grill heating elements GH (top)
Convection heating element CH
COMPONENT TEST
Resistance
Approximately 44.4 Ω (22.2 Ω x 2)
Approximately 42.5 Ω
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