R-654M (serv.man5). Complete - Sharp Home Appliance Service Manual (repair manual). Page 6

R-654M -6

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, and also the control unit is divided into two units, CPU Unit and Power Unit, and
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. Replacing the control unit.

2-1  In connection with pads.

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  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.
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.

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 stop switch operates properly; that is the contacts
are closed when the door is closed and open when the door is open. If the stop switch is good,
disconnect the flat ribbon cable that connects the key unit to the control unit and make sure the
stop switch is closed (either close the door or short the stop switch connecter). Use the Key unit
matrix indicated on 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.

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