DOWNLOAD Sharp R-90GCK (serv.man17) Service Manual ↓ Size: 1.28 MB | Pages: 48 in PDF or view online for FREE

15

b. Disconnect wire leads from the heating element  and measure the insulation resistance with

500V - 100M

Ω

 insulation resistance meter. The insulation resistance between heating element

terminal and cavity should be more than 0.5M

Ω

.

3. If the meter does not indicate above resistance, replace the side heating element.
4. CARRY OUT 4R CHECKS.

1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to “BACK PLATE REMOVAL”.
3. Disconnect connector-E from the control unit. Measure the resistance of the thermistor with an

ohmmeter. Connect the ohmmeter leads to Pin No’s E-5 and E-6.

Room Temperature

Resistance

68˚F(20˚C) - 86˚F(30˚C)

Approx. 360 k

Ω

 - 152 K

Ω

4. If the meter does not indicate above resistance, replace the thermistor.

5. CARRY OUT 4R CHECKS.

When the power cord is plugged into the wall receptacle and the rated voltage is supplied to the
damper motor, the motor operates until the damper is opened and the damper switch closes. Then
the damper motor stops operation.
If the damper motor does not operate, check for A.C. voltage with a voltmeter at the motor.
1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to “BACK PLATE REMOVAL”.
3. Disconnect the leads to the primary of the high voltage transformer.
4. Ensure that the leads remain isolated from other components and oven chassis by using insulation

tape.

5. Disconnect the wire leads of motor and connect the meter leads to the wire leads of main wire

harness.

6. Reconnect the power cord into the wall receptacle.
7. If the rated voltage is indicated at the wire leads, replace the motor and  if the rated voltage is not

indicated, check the wire harness and control unit.

8. Disconnect the oven from power supply.
9. Open the door and wedge it open.
10.Discharge high voltage capacitor.
11.CARRY OUT 4R CHECKS.

1. CARRY OUT 3D CHECKS.
2. Disconnect the leads to the primary of the high voltage transformer.
3. Ensure that the leads remain isolated from other components and oven chassis by using insulation

tape.

4. Disconnect the wire leads from the switch terminals and connect ohmmeter leads to the common

(COM.) and normally open (N.O.) terminals of the switch.

4-1. When switch actuator is pushed by the damper motor cam, the meter should be indicated a

closed circuit.

4-2. When power cord is plugged into the wall receptacle, the damper motor operates and damper

cam will start to rotate. When the switch actuator is released, the meter should be indicated an
open circuit.

5. If improper operation is indicated, replace the damper switch.
6. Disconnect the oven from power supply, and then remove outer case.
7. Open the door and wedge it open.
8. Discharge high voltage capacitor.
9. CARRY OUT 4R CHECKS.

16

BLK

RED

WHT

Main Coil

3-pin 
Connector

Sub Coil

Thermal

Cut-out

130˚C OFF
100˚C ON

130

Ω

140

Ω

CONVECTION MOTOR

1. CARRY OUT 3D CHECKS.
2. Disconnect input leads and check for short or open between the terminals using an ohmmeter.

Checking with a high ohm scale, if the capacitor is normal, the meter will indicate continuity for a
short time and should indicate an open circuit once the capacitor is charged. If the above is not
the case, check the capacitor with an ohmmeter to see if it is shorted between the terminals. If it
is shorted, replace the capacitor.

3. CARRY OUT 4R CHECKS.

1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to “BACK PLATE REMOVAL”.
3. Disconnect the 3-pin connector of the convection motor from the main wire harness.
4. Measure the resistance of the convection motor with an ohmmeter.

The resistance of the main coil, across the black and the red wires, should be approximately 130
ohms. The resistance of the sub coil, across the black and the white wires, should be
approximately 140 ohms.

5. Also, the convection motor has the thermal cut-out in it.

Measure the resistance of the main coil (or the sub coil). The resistance across the black and the
red wires (or across the black and the white wires) should be above resistance unless the
temperature of the thermal cut-out reaches approximately 130˚C. The thermal cut-out resets
automatically at 100˚C. If an ohmmeter
indicates an open circuit under normal
condition, replace the convection motor
because the thermal cut-out has opened. An
open thermal cut-out indicates overheating of
the convection motor. Check for restricted air
flow to the convection motor or a lock of the
convection fan, especially the fan motor (high
voltage transformer side).

6. CARRY OUT 4R CHECKS.

It is difficult to measure the exact temperature in the convection oven. An accurate thermocouple type
temperature tester must be used. A low priced bi-metal type thermometer is not reliable or accurate.
The temperature should be checked with outer case cabinet installed, approx. 5 minutes after preheat
temperature is reached (audible signal sounds four times). The temperature experienced may be
approx. 17˚C more or less than indicated on the display, however, in most cases the food cooking
results will be satisfactory.
Difference in power supply voltage will also affect the oven temperature. The Household power supply
voltage may sometimes become lower than the rated voltage and cause under-cooking. If the power
supply voltage is 10% lower than the rated voltage, longer cooking time is required by 10% to 20%.

1. CARRY OUT 3D CHECKS.
2. Remove the back plate from the oven, referring to “BACK PLATE REMOVAL”.
3. Disconnect the leads from the motor. Using an ohmmeter, check the resistance between the two

terminals as described in the table below.

Table: Resistance of Motor

Motors

Resistance

Fan motor

Approximately 77 

Ω

Turntable motor

Approximately 12 k

Ω

Damper motor

Approximately 11 k

Ω

If incorrect readings are obtained, replace the motor.
4. CARRY OUT 4R CHECKS.

17

The touch control panel consists of circuits including semiconductors such as LSI, ICs, etc. Therefore,
unlike conventional microwave ovens, proper maintenance cannot be performed with only a
voltmeter and ohmmeter. In this service manual, troubleshooting by unit replacement is described
according to the symptoms indicated.
Before testing,

1) CARRY OUT 3D CHECKS.
2) Disconnect the leads to the primary of the high voltage transformer.
2) Ensure that these leads remain isolated from other components and oven chassis by using

insulation tape.

1.  Tact switch

NOTE ;
1) Reinstall the outer case (cabinet).
2) Reconnect the power supply cord after the outer case is installed.
3) Run the oven and check all functions.

The following symptoms indicate a defective tact switch.

a) When touching the pads, a certain pad produces no signal at all.
b) When touching a number pad, two figures or more are displayed.
c) When touching the pads, sometimes a pad produces no signal.
If the tact switch is defective.
1) CARRY OUT 3D CHECKS.
2) Replace the CPU unit.
3) CARRY OUT 4R CHECKS.

2. Control Unit

The following symptoms  indicate a defective control unit.  Before replacing the control unit,
perform the tact switch test (Procedure W) to determine if control unit is faulty. Reconnect the
power supply cord. And  check for followings.

2-1 In connection with pads.

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.

2-2 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.
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.

2-3 Other possible problems 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.
d) Proper temperature measurment is not obtained.

When testing is completed, CARRY OUT 4R CHECKS.

1.

CARRY OUT 3D CHECKS.

2.  By using an ohmmeter, check the tact switch operation.
3. When the tact switch is not depressed, an ohmmeter should indicate an open circuit. When the

tact switch is depressed, an ohmmeter should indicate a short circuit. If improper operation is
indicated, the tact switch is probably defective and should be checked.

1. CARRY OUT 3D CHECKS.
2. Disconnect the leads to the primary of the high voltage transformer.
3. Ensure that these leads remain isolated from other components and oven chassis by using

insulation tape.

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

18

Solid-state relay

2

1

4

3

5. Remove the outer case and check voltage between Pin Nos. 1 and 9 of the 5 pin connector (CN-

D) on the control unit with an A.C. voltmeter. The meter should indicate the rated voltage, if not
check oven circuit.

Shut-off, Cook and Heater Relays 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, grill,
dual1, dual2, preheating, or convection cooking condition.
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 defective.

 

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

Approx. 18V D.C.

Oven lamp / Turntable motor

RY2 (COOK)

Approx. 18V D.C.

High voltage transformer

RY3

Approx. 24V D.C.

Convection motor

RY4

Approx. 24V D.C.

Damper motor

RY5

Approx. 24V D.C.

Fan motor

RY6

Approx. 24V D.C.

Convection motor

6. CARRY OUT 4R CHECKS.

1. CARRY OUT 3D CHECKS.
2. Disconnect the wire leads from the solid-state relay.
3. Measure the resistance between the terminals as described in the following table, with an

ohmmeter.

Terminals

Resistance

Between 1 and 2

Approx. 50M

Ω

Between 3 and 4

Approx. 1.3M

Ω

4. If the meter does not indicate above resistance, replace the solid-state relay.

5. CARRY OUT 4R CHECKS.

To protect the electronic circuits, this model is provided with a fuse added to the primary on the PWB.
1. Fuse 1 check and repairs and touch control transformer test.

1) CARRY OUT 3D CHECKS.
2) If the Fuse 1 is blown, replace the power unit.
3)  Make a visual inspection of the varistor. Check for burned damage and examine the touch

control transformer with a tester for the presence of layer short-circuit (check the primary coil
resistance which is approximately 275

Ω

 

±

 10%). If any abnormal condition is detected, replace

the touch control transformer or power unit.

4) CARRY OUT 4R CHECKS.

2. Follow the troubleshooting guide given below, if indicator does not light up after above check and

repairs are finished.
1) CARRY OUT 3D CHECKS.
2) Disconnect the leads to the primary of the high voltage transformer.
3) Ensure that these leads remain isolated from other components and oven chassis by using

insulation tape.

4) After that procedure, re-connect the power supply cord.
5) Follow the troubleshooting guide given below for repair.

STEPS

OCCURRENCE

CAUSE OR CORRECTION

1

The rated AC voltage is not present to power

Check supply voltage and oven power cord.

terminal of CPU connecter (CN-D).

2

The rated AC voltage is present at primary

Low voltage transformer or secondary circuit defective.

side of low voltage transformer.

Check and repair.

6) CARRY OUT 4R CHECKS.