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R-291(K)M

8 – 3

If incorrect readings are obtained, make the necessary switch adjustment or replace the switch.

CARRY OUT 4R  CHECKS.

CARRY OUT 3D CHECKS.

Disconnect the leads from the terminals of the temperature fuse. Then using an ohmmeter, make a continuity test across the two terminals as
described in the below.

If incorrect readings are obtained, replace the temperature fuse.

g produced by

improper setting of the cooking time or failure of the control panel.

CARRY OUT 4R  CHECKS.

CARRY OUT 3D CHECKS.

Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two terminals as described in the table below.

If incorrect readings are obtained, replace the motor.

CARRY OUT 4R  CHECKS.

CARRY OUT 3D CHECKS.

If the fuse T6.3A is blown when the door is opened, check the monitored latch switch, relay (RY1), timer switch and monitor switch.

If the fuse T6.3A is blown by incorrect door switching replace the defective switch(es) and the fuse T6.3A.

If the fuse T6.3A is blown, there is a shorts or grounds in electrical parts or wire harness. Check them and replace the defective parts or repair the
wire harness.

CARRY OUT 4R  CHECKS.

CAUTION: ONLY REPLACE FUSE T6.3A WITH THE CORRECT VALUE REPLACEMENT.

CARRY OUT 3D CHECKS.

Check them and replace the defective parts and the high voltage fuse.

CARRY OUT 4R  CHECKS.

CAUTION: ONLY REPLACE HIGH VOLTAGE FUSE  WITH THE CORRECT VALUE REPLACEMENT. 

Table: Temperature Fuse Test

Parts Name

Temperature of “ON” condition 

(closed circuit).

Temperature of “OFF” condition 

(open circuit).

Indication of ohmmeter (When room 
temperature is approx. 20

C.)

Temperature fuse 150

C

This is not resetable type.

Above 150

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Table: Resistance of Motor

Motors

Resistance

Fan motor

Approximately 250 

Turntable motor

Approximately 14.7 k

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore, unlike conventional mic rowave 
ovens, proper maintenance cannot be performed with only a voltmeter and ohmmeter. In this service manual, the touch control pan el 
assembly is divided into two units, Control Unit and Key Unit, and also the Control Unit is divided into two units, CPU Unit an d Power 
Unit, and troubleshooting by unit replacement is described according to the symptoms indicated.

1. Key Unit. Note: Check key unit ribbon connection before replacement.

 The following symptoms indicate a defective switch unit. Replace the switch unit.

a) When touching the Pads, a certain Pad produces no signal at all.

b) When touching the Pads, sometimes a Pad produces no signal.

c) When rotating the TIMER/WEIGHT knob, the cooking time or the weight can not be input.

2. Control Unit.

 The following symptoms indicate a defective control unit. Before replacing the control unit, perform the Key unit test ([11]  Procedure K)

to determine if control unit is faulty. 

 1) In connection with buttons.

 a) When touching the Pads, a certain group of Pads do not produce a signal. 

 b) When touching the Pads, no Pads produce a signal.

 2) In connection with indicators.

 a) At a certain digit, all or some segments do not light up.

 b) At a certain digit, brightness is low.

 c) Only one indicator does not light up. 

 d) The corresponding segments of all digits do not light up; or they continue to light up.

 e) Wrong figure appears.

 f) A certain group of indicators do not light up.

 g) The figure of all digits flicker.

 3) Other possible troubles caused by defective control unit.

 a) Buzzer does not sound or continues to sound.

 b) Clock does not operate properly.

 c) Cooking is not possible.

If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable is making good contact, ve rify 
that the 2nd. interlock relay control switch operates properly; that is the contacts are closed when the door is clo sed and open when 
the door is open. If the 2nd. interlock relay control switch is good, disconnect the flat ribbon cable that connects the key uni t to the 
control unit and make sure the 2nd. interlock relay control switch is closed (either close the door or short the 2nd. interlock  relay control
switch connector). Use the key unit matrix indicated on the control panel schematic and place a jumper wire between the pins th at 
correspond to the STOP/CLEAR pad making momentary contact. If the control unit responds by clearing with a beep the key unit is  
faulty and must be replaced. If the control unit does not respond, it is faulty and must be replaced. If a specific pad does not  respond, 
the above method may be used (after clearing the control unit) to determine if the control unit or keypad is at fault.

R-291(K)M

8 – 4

CARRY OUT  3D  CHECKS.
Remove the outer case and check voltage between the pin No.1 of connector CN-B and the oven side terminal of the relay 
RY1 on the control unit with an A.C. voltmeter. The meter should indicate 230 - 240 volts, if not check oven circuit.

RY1 and RY3 Relay Test
These relays are operated by D.C. voltage
Check voltage at the relay coil with a D.C. voltmeter during the microwave cooking operation.

DC. voltage indicated  .................. Defective relay.
DC. voltage not indicated ............ Check diode which is connected to the relay coil. If diode is good, control unit is defec tive.

RY2, RY3

Approx. 12.8 V D.C.

Oven lamp / Turntable motor / Cooling fan motor

RY1

Approx. 12.3V D.C.

High voltage transformer

CARRY OUT  4R  CHECKS.

To protect the electronic circuits, this model is provided with a Thermal fuse in low voltage transformer on the PWB, follow 

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Problem: POWER ON, indicator does not light up.
CARRY OUT  3D  CHECKS.

1

the pin No.1 of connector CN-B and the oven side terminal of

the relay RY1

Check supply voltage and oven power cord.

2

The rated AC voltage is present to primary side of low voltage transformer. Low voltage transformer or secondary circuit defective.

Check and replace the control unit.

R-291(K)M

8 – 5

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

(1) Key Unit 

(2) Control Unit

The principal functions of these units and their related signals 
are explained below.

1. Key Unit

The key unit is composed of a matrix, signals generated in the 
LSI are sent to the key unit through P123, P124, P132 and 
P133. When a key pad is touched, a signal is completed 
through the key unit and passed back to the LSI through
P40, P41 and P42 to perform the function that was requested.

2. Control Unit

Control unit consists of LSI, reset circuit, indicator circuit, power 
source circuit, relay circuit, buzzer circuit and synchronizing sig -
nal circuit. 

1) Reset Circuit

 This circuit generates a signal which resets the LSI to the 

initial state when power is supplied.

2) Indicator Circuit

 This circuit consists of 3-digits, 11-segments and 3-common 

electrodes using a Liquid Crystal Display.

3) Power Source Circuit

 This circuit generates voltage necessary in the control unit 

from the AC line voltage. In addition, the synchronizing sig -
nal is available in order to compose a basic standard time in 
the clock circuit.

Symbol

Voltage

Application

VCC

5V

LSI(I1)

4) Relay Circuit

 To drive the magnetron, fan motor, turntable motor and light 

the oven lamp.

5) Buzzer Circuit

 The buzzer is responsive to signals from the LSI to emit 

audible sounds (switch unit touch sound and completion 
sound).

6) Synchronizing Signal Circuit

 The power source synchronizing signal is available in order 

to compose a basic standard time in the clock circuit. It ac -
companies a very small error because it works on commer-
cial frequency.

7) 2nd. Interlock Relay Control Switch

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

The “Main PWB” of this model employs lead-free solder. This is indicated by the “LF” symbol printed on the PWB and in the service 
manual. The suffix letter indicates the alloy type of the solder.

Indicates lead-free solder of tin, copper and nickel

When repairing a PWB with the “LF” symbol, only lead-free solder should be used. (Using normal tin/lead alloy solder may result in 
cold soldered joints and damage to printed patterns.)
As the melting point of lead-free solder is approximately 40°C higher than tin/lead alloy solder, it is recommend that a dedicated bit is 
used, and that the iron temperature is adjusted accordingly.

As the melting point of lead-free solder (Sn-Cu-Ni) is higher and has poorer wettability (flow), to prevent damage to the land of the 
PWB, extreme care should be taken not to leave the bit in contact with the PWB for an extended period of time. Remove the bit as 
soon as a good flow is achieved.
The high content of tin in lead free solder will cause premature corrosion of the bit. To reduce wear on the bit, reduce the temperature 

tics, making 

good soldering more difficult. It will be necessary to clean and replace bits more often when using lead-free solder. To reduce bit wear, 
care should be taken to clean the bit thoroughly after each use.

R-291(K)M

9 - 1