Sharp R-4P58 Service Manual page 18

A-AP58
R-4PS(5K)
A-4P5
A-4PSEWIF
PROCEDURE
LETTER
L
TEST PROCEDURES (CONT'D)
COMPONENT TEST
GRILL HEATING ELEMENT (TOP} AND BOTTOM HEATING ELEMENT TEST
CARRY OUT 3D CHECKS.
Before carrying out the fallowing tests make sure the heating element is cool completely.
1. Resistance of heating element.
Disconnect the wire leads to the heating elementio be tested. Using ohmmeter with low resistance
range. Check the resistance across the terminals of the heating element as described in the
foliowing table.
Table: Resistance of heating element
Grill heating element (top) Approximately 22.5 2 x 2 = 45 Q
Bottom heating element Approximately 66 Q -
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 - 100MQ insulation tester. The insulation
resistance should be more than 10 MQ in the cold start.
lf 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.
I H CONTROL PANEL ASSEMBLY TEST
The touch contro! 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 chmmeter.
In this service manual, the touch control panel assembly is divided into two units, Control Unit and Key
Unit, and troubleshooting by replacement is described according to the symptoms indicated.
1. Key Unit Note : Check key unit ribbon connection before replacement.
The following symptoms indicate a defective key unit. Replace the key unit.
a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.
2. Control Panel
The following symptoms indicate a defective coniro! unit. Before replacing the control unit, perform
the key unit test (Procedure N) to determine if control unit is faulty.
2-1 In connection with pads
@) When touching the pads, a certain group of pads do not produce a signal.
b) When touching the pads, no pads produce a signal.
2-2 In connection with indicators
a) At acertain digit, all or some segments do not light up.
b) At acertain 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.
€) Wrong figure appears.
f) Acertain group of indicators do not light up.
g) The figure of all digits flicker.
2-3 Other possible troubles caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
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"c) Cooking is not possible.
KEY UNIT TEST
lf the display fails to clear when the STOP pad is depressed, first verify the flat ribbon is marking good
contact, verify that the door sensing switch (stop switch) operates properly; that is the contacts are
closed when the door is closed and open when the door is open. Ifthe door sensing switch (stop switch)
is good, disconnect the flat ribbon cable that connects the key unit to the control unit and make sure
ihe door sensing switch is closed (either close the door or short the door sensing switch connecter).
Use the Key unit matrix indicated on the control panel schematic and place a jumper wire between the
pins that correspond to the STOP pad marking momentary contact. If the control unit responds by
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