R-2287 - Sharp Home Appliance Service Manual (repair manual). Page 20

18

The control section consists of the following units as
shown in the touch control panel circuit.

(1) Control Unit
(2) Key Unit

The principal functions of these units and the signals
communicated among them are explained below.

Signal of key touch and oven function control are all
processed by one microcomputer.

This circuit changes output voltage at the secondary
side of the low voltage (T1) transformer to volatges
required at each part by full wave rectifying circuit,
constant voltage circuit, etc..

This is an Auto-clear Circuit, i.e., a reset circuit, which
enables IC1 to be activated from initial state.

This is a circuit for generating power SYNC signal by
virtue of the secondary side output of transformer T1.
This signal is used for a basic frequency to time
processing and so on.

This is a circuit for controlling clock frequency required
for operating IC1.

This is a one-chip microcomputer, responsible for
controlling the entire control unit.

This is a circuit for driving display tubes by IC1 output.

This is a circuit for transmitting switch input informa-
tion to IC1.

This is a circuit for driving sound body by IC1 output.

This is a circuit for driving output relay by IC1 output.

This is a circuit for driving IC1 to detect door opening/
closing.

This is a circuit for transmitting output change of

OUTLINE OF CONTROL PANEL

thermistor (Exhaust Air Temperature Sensor) to IC1.

This circuit detects problems in the magnetron / high
voltage circuit by sensing a variation in the current
flowing through the primary winding of the high voltage
transformer.
During heating, the primary current of the high voltage
transformers also flows through the primary winding of
the current transformers CT1 and CT2. This causes a
current to be induced in the secondary windings of
CT1/CT2 and results in an AC voltage  which is
determined by R30/R31.
This AC voltage is then half wave rectified by D30/D31
and smoothed (filtered) by C30/C31.
This AC voltage is the input to the AN3 and AN4 ports
of IC1, which determines if there is a magnetron / high
voltage problem.

HIGH VOLTAGE TRANSFORMER

HIGH VOLTAGE CIRCUIT
MAIN BODY SIDE

T/C SIDE

CT1 or CT2

RY2 or RY3

R30 or
R31

R65 or
R66

D30 or
D31

R32 or
R33

Vc

C30 or C31

IC1
AN3 or
AN4 PORT

D32 or
D33

This is a circuit for transmitting output change of
thermistor (Magnetron Temperature Sensor) to IC1.

This is a circuit for transmitting output change of
thermistor (Intake Air Sensor) to IC1.

The switch unit is composed of a matrix circuit in which
when a switch it touched, one of signals P43 - P45
generated by the LSI, is passed through the switch
and returned to the LSI as one of signals P50 - P51.

The encoder converts the signal generated by LSI into
the pulse signal, and the pulse signal is returned to the
LSI.