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R899(WH)

9 – 1

R899(WH)

Service Manual

 

The control section consists of the following units as shown in the con-
trol panel circuit.

(1)Jog Switch Unit

(2) Control Unit

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

The jog switch unit is composed of a matrix, signals generated in the
LSI are sent to the jog switch unit from P44 – P47.

When a button is touched, a signal is completed through the jog switch
unit and passed back to the LSI through P00, P20, P21 and P22 to
perform the function that was requested.

Control unit consists of LSI, power source circuit, synchronizing signal
circuit, reset circuit, buzzer circuit, indicator circuit, encoder circuit,
potentiometer circuit, temperature measurement circuit and back light
circuit.

1) LSI

This LSI controls the temperature measurement signal, tact switch
strobe signal, relay driving signal for oven function and indicator
signal.

2) Power Source Circuit

This circuit generates voltage necessary in the control unit.

3) Synchronizing Signal Circuit

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

4) Reset Circuit

A circuit to generate a signals which resets the LSI to the initial
state when power is supplied.

5) Buzzer Circuit

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

6) Stop Switch

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

7) Relay Circuit

To drive the magnetron, top and bottom heating element, convec-
tion motor, fan motor, turntable motor, touch control transformer
and light the oven lamp.

8) Encoder

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

9) Potentiometer Circuit

The circuit makes setting of the cooking mode by variable resis-
tance.

10)Back Light Circuit

A circuit to drive the back light (Light emitting diodes LD1 - LD10).

11)Indicator Circuit

This circuit consists 7-digits, 27-segments and 4-common elec-
trodes using a Liquid Crystal Display.

12)Temperature Measurement Circuit: (OVEN THERMISTOR)

The temperature in the oven cavity is sensed by the thermistor. The
variation of resistance according to sensed temperature is detected
by the temperature measurement circuit and the result applied to
LSI. The LSI uses this information to control the relay and display
units.

Symbol

Voltage

Application

VC

-5.2V

LSI(IC1)

R899(WH)

9 – 2

This unit uses CMOS LSI in the integral part of the circuits. When han-
dling these parts, the following precautions should be strictly followed.
CMOS LSI have extremely high impedance at its input and output ter-
minals. For this reason, it is easily influenced by the surrounding high
voltage power source, static electricity charge in clothes, etc., and
sometimes it is not fully protected by the built-in protection circuit.

In order to protect CMOS LSI.

1) When storing and transporting, thoroughly wrap them in aluminium

foil. Also wrap PW boards containing them in aluminium foil.

2) When soldering, ground the technician as shown in the figure and

use grounded soldering iron and work table.

We describe the procedures to permit servicing of the control panel of
the microwave oven and the precautions you must take when doing
so. To perform the servicing, power to the control panel is available
either from the power line of the oven or from an external power
source.

1. Servicing the control panel with power supply of the oven:

CAUTION: THE HIGH VOLTAGE TRANSFORMER OF THE MICRO-

WAVE OVEN IS STILL LIVE DURING SERVICING AND
PRESENTS A HAZARD.

Therefore, before checking the performance of the control panel,

1) Disconnect the power supply cord, and then remove outer case.

2) Open the door and block it open.

3) Discharge high voltage capacitor.

4) Disconnect the leads to the primary of the power transformer.

5) Ensure that these leads remain isolated from other components

and oven chassis by using insulation tape.

6) After that procedure, re-connect the power supply cord.

After checking the performance of the control panel,

1) Disconnect the power supply cord.

2) Open the door and block it open.

3) Reconnect the leads to the primary of the power transformer.

4) Reinstall the outer case (cabinet).

5) Reconnect the power supply cord after the outer case is installed.

6) Run the oven and check all functions.

a) On some models, the power supply cord between the control

panel and the oven is so short that the two can't be separated.

For those models, check and repair all the controls (sensor-
related ones included) of the control panel while keeping it con-
nected to the oven.

b) On some models, the power supply cord between the control

panel and the oven is long enough that they may be separated
from each other. For those models, therefore, it is possible to
check and repair the controls of the control panel while keeping
it apart from the oven; in this case you must short both ends of
the door sensing switch (on PWB) of the control panel with a
jumper, which brings about an operational state that is equiva-
lent to the oven door being closed. As for the sensor related
controls of the control panel, checking them is possible if the
dummy resistor(s) with resistance equal to that of the controls
are used.

2. Servicing the control panel with power supply from an exter-

Disconnect the control panel completely from the oven, and short
both ends of the door sensing switch (on PWB) of the control panel,
which brings about an operational state that is equivalent to the
oven door being closed. Connect an external power source to the
power input terminal of the control panel, then it is possible to
check and repair the controls of the control panel; it is also possible
to check the sensor-related controls of the control panel by using
the dummy resistor(s).

Tools required to service the control panel assembly.

1) Soldering iron: 60W

(It is recommended to use a soldering iron with a grounding termi-
nal.)

2) Oscilloscope: Single beam, frequency range: DC - 10MHz type or

more advanced model.

3) Others: Hand tools

1) Before turning on the power source of the control unit, remove the

aluminium foil applied for preventing static electricity.

2) Connect the connector of the switch unit to the control unit being

sure that the lead wires are not twisted.

3) After aluminium foil is removed, be careful that abnormal voltage

due to static electricity etc. is not applied to the input or output ter-
minals.

4) Attach connectors, electrolytic capacitors, etc. to PWB, making

sure that all connections are tight.

5) Be sure to use specified components where high precision is

required.

approx. 1M ohm