Specifications

Ver SG 9/200 32 Sharp Electronics Corporation
Control Panel Circuit
The key unit is a switching device. When a keypad is touched it will momentarily switch
an output signal from the microcontroller to the input ports of that same microcontroller.
The door sensing switch must be closed and working properly, as this switch is
responsible for enabling the input section of the microcontroller. The input command
will be recognized by the ROM section of the microcontroller and the desired command
will be executed.
To diagnose a failure in the key unit, disconnect the mylar ribbon connector between the
key unit and the control unit. With a small diameter solid wire, jump across the key
function which has the suspected failure. As an example, if an R-530BK will not clear
the display from the initial “flashing 8” condition, disconnect the ribbon connector and
insert the jumper wire on the control board connector at G1 and G12 (see page 33 for
layout of Key Unit for the R-530BK/BW). Of course the door must be closed and the
door sensing switch must be operating properly before this test can be made. If a beep is
heard and the display clears, the problem would be in the key unit. If the control does not
respond when the jumper connection is made the problem is in the control unit. Any pad
on the key unit can be tested in this same manner. However, keep in mind the
microcontroller is sequentially programmed. This means certain commands must be
entered ahead of others. As an example, the control must first be cleared, the clock set,
cooking time entered, and the start key touched. If we try to start the unit before time is
entered, the control will not respond.
To diagnose a failure in the control unit, place a voltmeter across the power input
terminals. Refer to the power unit circuit on page 34, model R-530BK. As an example,
if the display is dead and the control will not accept commands from the key unit proceed
as follows. Place a voltmeter across terminals A-1 and Common on the Power Unit
Circuit Board. 120 volts should be indicated on the meter. If zero volts is indicated, the
problem is in the circuitry ahead of the control assembly such as an open monitor fuse.
Do not condemn the control if this condition exists. If 120 volts is indicated across A-1
and Common further testing is required. With a voltmeter, check across the primary
windings of the low voltage transformer “T1”. The meter should indicate 120 volts. If
the voltage is present, the control is not accepting commands, and the display is dead,
replace the control assembly. If the meter indicates zero volts across the primary winding
of the transformer “T1” but 120 volts was indicated across A-1 and Common, check the
foil pattern between the two test points. When you locate the open foil proceed with the
repair procedure on page 35.
Control assemblies for microwave ovens are considered as a replaceable part once the
foil pattern repair is checked.
THIS PROCEDURE MUST BE FOLLOWED PRIOR TO CONDEMNING A
CONTROL ASSEMBLY ON ALL THE SOLID STATE CONTROLS FOR THIS
PRODUCT YEAR.