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1. Digital Readout
2. DOUBLE QUANTITY pad
3. EXPRESS DEFROST pad
4. Number pads for time and memory program-

ming

5. SELECT TIME pad
6. STOP/CLEAR pad; touch to stop operation of

oven and clear remaining heating time

7. SELECAT POWER pad for setting variable

power level

8. START pad; touch to operate oven after door

is closed and time is set

9. SET pad for setting memory
10.CHECK pad for checking memory
11.SIGNAL pad for setting signal sound

1. Oven light
2. Ceramic shelf
3. Control panel
4. Cavity face plate
5. Door latch openings
6. Door latches
7. Door hinges
8. Door seals and sealing surfaces
9. Door handle
10.Oven door with see-through window
11.Air ventilation cover and openings
12.Power supply cord
13.Air intake openings
14.Outer case cabinet

When this commercial  microwave oven is installed near other commercial electrical appliances, connect a lead wire to
each equivalent potential terminal with equipotential marking between them (insert a lead wire between a washer and
an earth angle, and screw them), as shown in Fig. A-1, to make sure that they are at equivalent potential.
If any lead wire is not connected between them, when person touch them he/she will get a electric shock.

COMMERCIAL MICROWAVE OVEN

OTHER COMMERCIAL 
ELECTRICAL APPLIANCE

Lead wire

Equipotential marking

Earth angle
(Equipotential terminal)

Equipotential 
terminal

Screw

Washer

Lead wire

DEF

ON

NO. X2 CHECK

1

3

4

6
8
11

2

5

7
9
10

12

11

7

10

9

5

4

3

13

14

8

1

2

6

4

Closing the door activates the 1st. latch switch, 2nd. latch
switch and stop switch.

1. The oven display will show        .        .

Program desired cooking time by touching SELECT TIME
pad and the NUMBER pads. When the START pad is
touched, the following operations occur:

RELAY

CONNECTED COMPONENTS

RY-2

power transformer

RY-3

oven lamp/antenna motor/fan motor

1. The line voltage is supplied to the primary winding of

the high voltage transformer. The voltage is converted
to about 3.3 volts A.C. output on the filament winding
and high voltage of approximately 2300 volts A.C. on
the secondary winding.

2. The filament winding voltage (3.3 volts) heats the

magnetron filament and the high voltage (2000 volts) is
sent to the voltage doubling circuit, where it is doubled
to negative voltage of approximately 4000 volts D.C..

3. The 2450 MHz microwave energy produced in the

magnetron generates a wave length of 12.24 cm. This
energy is channelled through the waveguide (transport
channel) into the oven cavity, where the food is placed
to be cooked.

4. When the cooking time is up, a signal tone is heard and

the relays RY2 + RY3 go back to their home position.
The circuits to the oven lamp, high voltage transformer,
fan motor and antenna motor are cut off.

5. When the oven door is opened during a cooking cycle,

the switches come to the following condition.

Switch

Contact

          Condition
During

Oven Door

Cooking

Open(No cooking)

1st. interlock switch

COM-NO

Closed

Opened

Latch switch

COM-NO

Closed

Opened

2nd. interlock relay
control switch

COM-NO

Closed

Opened

Monitor Switch

COM-NC

Opened

Closed

The circuit to the high voltage transformer, fan motor, oven
lamp and antenna motor are cut off when the 1st. interlock
switch, latch switch and 2nd. interlock relay control switch
are made open. Shown in the display is remaining time.

6. MONITOR SWITCH CIRCUIT

The monitor switch is mechanically controlled by the
oven door, and monitors the operation of the 1st.
interlock switch.

6-1. When the oven door is opened during or after the

cycle of a cooking program, the  1st. interlock switch,

latch switch and 2nd. interlock relay control switch
must open their contacts first. After that the contacts
(COM-NC) of the monitor switch can be closed.

6-2. When the oven door is closed, the contacts (COM-

NC) of the monitor switch must be opened. After that
the contacts of the 1st. interlock switch, latch switch
and 2nd. interlock relay control switch  are closed.

6-3. When the oven door is opened and the contacts of the

1st. latch switch, 2nd. latch switch and the relay RY2
remain closed, the fuse M10A will blow, because the
monitor switch is closed  and a short circuit is caused.

When Variable Cooking Power is programmed, the line
voltage is supplied to the power transformer intermittently
through the contacts of relay (RY-2) which is operated by
the control unit within a 32 second time base. Microwave
power operation is as follows:

VARI-MODE

ON TIME

OFF TIME

Power 10(P-HI)

32 sec.

0 sec.

(100% power)
Power 9(P-90)

30 sec.

2 sec.

(approx. 90% power)
Power 8(P-80)

26 sec.

6 sec.

(approx. 80% power)
Power 7(P-70)

24 sec.

8 sec.

(approx. 70% power)
Power 6(P-60)

22 sec.

10 sec.

(approx. 60% power)
Power 5(P-50)

18 sec.

14 sec.

(approx. 50% power)
Power 4(P-40)

16 sec.

16 sec.

(approx. 40% power)
Power 3(P-30)

12 sec.

20 sec.

(approx. 30% power)
Power 2(P-20)

 8 sec.

24 sec.

(approx. 20% power)
Power 1(P-10)

 6 sec.

26 sec.

(approx. 10% power)
Power 0(P-0)

 0 sec.

32 sec.

(0% power)

Note:

The ON/OFF time ratio does not correspond with
the percentage of microwave power, because
approx. 2 seconds are needed for heating of the
magnetron filament.

5

The door is opened by grasping the door handle, refer to
Figure D-1.
When the door handle is grasped, the handle lever is
pulled. And then the upper and lower latch heads are
moved upward by the handle lever, and they are re-
leased from the latch hook. Now the door will open.

1. When the oven door is closed, the contacts (COM-NO)

of each switch must be closed.

2. When the oven door is opened, the contacts (COM-

NO) of each switch must be opened.

1. When the door is closed, the contacts (COM-NC) must

be opened.

2. When the door is opened, the contacts (COM-NC)

must be closed.

3. If the oven door is opened and the contacts (COM-NO)

of the 1st. interlock switch fail to open, the fuse M10A
blows immediately after closing the contacts (COM-
NC) of the monitor switch.

CAUTION: BEFORE REPLACING A BLOWN FUSE

M10A TEST THE 1ST. INTERLOCK SWITCH,
MONITOR SWITCH AND MONITOR RESIS-
TOR FOR PROPER OPERATION.  (REFER
TO CHAPTER “TEST PROCEDURE”).

1. If the wire harness or electrical components are short-

circuited, this fuse blows to prevent an electric shock or
fire hazard.

2. This fuse blows when the 1st. interlock switch remain

closed with the oven door open and when the  contacts
(COM-NC) of monitor switch closes.

The high voltage fuse blows when the high voltage rectifier
or the magnetron is shorted.

This thermal cut-out protects the magnetron against over-
heating. If the temperature goes up higher than 145˚C
because the fan motor is interrupted or the ventilation
openings are blocked, the thermal cut-out  will open and
line voltages to the high voltage transformer will be cut off
and the operation of the magnetron will be stopped. The
thermal cut-out will not resume.

The thermal cut-out located on the top of the oven cavity
is designed to prevent damage to the oven if the food in the
oven catches fire due to over heating produced by im-
proper setting of the cooking time or failure of control unit.
Under  normal operation, the oven thermal cut-out re-
mains closed. However, when abnormally high tempera-
tures are reached within the oven cavity, the oven thermal
cut-out will open at 125˚C causing the oven to shut down.
The thermal cut-out will not resume.

The monitor resistor prevents the fuse M10A bursting
when the fuse M10A blows due to the operation of the
monitor switch.

The noise filter assembly prevents radio frequency inter-
ference that might flow back in the power circuit.

The antenna motor rotates the stirrer antenna located on
the bottom of the oven cavity, so that the food on the
ceramic shelf is cooked evenly during cooking. The an-
tenna motor may turn in either direction.

The cooling fan motor drives a blade which draws exter-
nal cool air. This cool air is directed through the air vanes
surrounding the magnetron and cools the magnetron.
This air is channelled through the oven cavity to remove
steam and vapors given off from the heating food. It is
then exhausted through the exhausting air vents at the
oven cavity.

Latch Hook

Latch Switch

Lever A

Latch Switch

Lever B

Latch Switch

Lever C

Latch Head

Latch Head

Handle

Lever

Door

Handle

Latch

Lever

1st. Interlock Switch

Monitor
Switch

2nd. Interlock Relay 
Control Switch

Latch Switch

6

When troubleshooting the microwave oven, it is helpful to follow the Sequence of Operation in performing the checks.
Many of the possible causes of trouble will require that a specific test be performed. These tests are given a procedure
letter which will be found in the “Test Procedure” section.

TEST PROCEDURE

CONDITION

PROBLEM

POSSIBLE CASE

AND 

DEFECTIVE PARTS

Home fuse or circuit 
breaker blows when 
power cord is plugged into 
wall outlet.

Fuse M10A blows when 
power cord is plugged into 
wall receptacle.

     .          does not appear 
in display when power 
cord is first plugged into 
wall outlet.

Oven lamp does not light 
when door is opened.

Oven lamp lights but fan 
motor and antenna motor 
do not operate.

Oven does not go into 
cook cycle when START 
pad is touched.

Oven seems to be 
operating but little or no 
heat is produced in oven 
load. (Food incompletely 
cooked or not cooked at 
all at end of cook cycle.)

Oven goes into a cook 
cycle but extremely 
uneven heating is 
produced in oven load 
(food).

Oven does not cook 
p r o p e r l y   w h e n  
programmed for Cooking 
Power 5 mode. (Operates 
properly on Cooking 
Power 10 (HIGH) mode.)

"EE9" Maximum time is 
exceeded.

OFF
CONDITION

COOKING
CONDITION

ERROR MODE

MAGNETRON

HIGH VOLTAGE TRANSFORMER

H.V. RECTIFIER ASSEMBLY

HIGH VOLTAGE CAPACITOR

THERMAL CUT-OUT

1ST. INTERLOCK SWITCH

LATCH SWITCH

FUSE M10A

HIGH VOLTAGE 

FUSE

NOISE FILTER

TOUCH CONTROL PANEL

KEY UNIT

EXCEED MAX. HEATING TIME

RELAY (RY3)

RELAY (RY2)

FOIL PATTERN ON P.W.B.

LOW VOLTAGE

WRONG OPERATION

DIRTY OVEN CAVITY

MISADJUSTMENT SWITCH

SHORTED IN POWER CORD

OVEN LAMP OR SOCKET

COOLING FAN MOTOR

ANTENNA MOTOR

SHORT OR OPENED WIRING

MONITOR SWITCH

2ND. INTERLOCK RELAY CONTROL SWITCH