Sharp R-240B Service Manual page 14

R-240B
PROCEDURE
LETTER
L TOUCH CONTROL PANEL ASSEMBLY TEST
The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlike conventional microwave ovens, proper maintenance cannot be performed with only a
voltmeter and ohmmeter.
In this service manual, the touch control panel assembly is divided into two units, Control Unit and
Key Unit, troubleshooting by unit replacement is described according to the symptoms indicated.
1. Key Unit.
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 Unit.
The following symptoms indicate a defective control unit. Replace the control unit.
2-1 Programming problems.
a) 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 Display problems.
a) For a certain digit, all or some segments do not light up.
b) For 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.
2-3 Other possible problems caused by defective control unit.
a) Buzzer does not sound or continues to sound.
b) Clock does not operate properly.
c) Cooking is not possible.
M KEY UNIT TEST
If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable
is making 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. If the door sensing
switch (stop switch) is good, disconnect the flat ribbon cable that connects the key unit to the control
unit and make sure the door sensing switch is closed (either close the door or short the door stop
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/CLEAR pad making momentary contact.
If the control unit responds by clearing with a beep, the key unit is faulty and must be replaced. If the
control unit does not respond, it is a faulty and must be replaced. If a specific pad does not respond,
the above method may be used (after clearing the control unit) to determine if the control unit or key
pad is at fault.
N RELAY TEST
Remove the outer case and check voltage between Pin No 3 of the 2 pin connector (A) and common
terminal (lower terminal) of the relay (RY2) on the control unit with an A.C. voltmeter.
The meter should indicate 230 - 240 volts, if not check oven circuit.
TEST PROCEDURES
COMPONENT TEST
G 6
G 7 BEVERAGE
FROZEN
G 8
VEGETABLES
RICE
G 9
PASTA
G10
12
G 5 G 4 G 3
JACKET
6 2
POTATO
3
5 4
TIMER
1
0
CLOCK
9 8
7
G 2 G 1
EASY
DEFROST
POWER
LEVEL
STOP
FRESH
VEGETABLES
CLEAR
INSTANT COOK
DINNER
PLATE START