R-752M (serv.man2) - Sharp Home Appliance Service Manual (repair manual). Page 7

7

752M -

CARRY OUT 3D CHECKS.

Isolate the high voltage rectifier assembly from the HV circuit. The high voltage rectifier  can
be tested  using an ohmmeter set to its highest range. Connect the ohmmeter across the
terminal of the high voltage rectifier and note the reading obtained. Reverse the meter leads
and note this second reading.
The normal resistance is infinite in one direction and more than 100 k

Ω

 in the other direction.

CARRY OUT 4R CHECKS.

NOTE:

FOR MEASUREMENT OF THE RESISTANCE OF THE RECTIFIER, THE
BATTERIES OF THE MEASURING INSTRUMENT MUST HAVE A VOLTAGE AT
LEAST 6 VOLTS, BECAUSE OTHERWISE AN INFINITE RESISTANCE
MIGHT BE SHOWN IN BOTH DIRECTIONS.

OUTLINE OF TOUCH CONTROL PANEL

The touch control section consists of the following units.

(1) Key Unit
(2) Control Unit (The Control Unit consists of Power Unit and

CPU Unit).

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

The key unit is composed of a matrix, signals generated in
the LSI are sent to the key unit through P20, P21, P22, P23,
P24, P25, P26 and P27.
When a key pad is touched, a signal is completed through
the key unit and passed back to the LSI through P43, P44,
P45 and P46 to perform the function that was requested.

Control unit consists of LSI, ACL circuit, indicator circuit,
power source circuit, relay circuit, buzzer circuit, synchro-
nizing signal circuit and back light circuit.

This circuit generates a signal which resets the LSI to the
initial state when power is supplied.

This circuit consists of 4-digits, 12-segments and 3
common electrodes using a Liquid Crystal Display.

This circuit generates voltages necessary in the control
unit from the AC line voltage.
In addition, the synchronizing signal is available in
order to compose a basic standard time in the clock
circuit.

Symbol

Voltage

Application

VC

-5.2V

LSI(IC1)

A circuit to drive the magnetron, grill heating element,
fan motor, turntable motor and  light the oven lamp.

The buzzer is responsive to signals from the LSI to emit
audible sounds (key touch sound and completion
sound).

The power source synchronizing signal is available in
order to compose a basic standard time in the clock
circuit.
It accompanies a very small error because it works on
commercial frequency.

A switch to “tell” the LSI if the door is open or closed.

A circuit to drive the back light (Light emitting diodes
LD1- LD5).