Procedure N: Key Unit (Membrane Switch) Test; Procedure O: Relay Test; Procedure P: Procedures To Be Taken When The Foil Pattern On The Printed Wiring Board (Pwb) Is Open - Sharp R-990KS Service Manual

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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.

[14] Procedure N: KEY UNIT (MEMBRANE SWITCH) TEST

If the display fails to clear when the STOP/CLEAR pad is depressed, first verify the flat ribbon cable is making good contact, verify that the door sens-

ing switch (stop switch) operates properly; that is the contacts are closed when the door is closed and open when the door is open. If the door sensing

switch (stop switch) is good, disconnect the flat ribbon cable that connects the key unit to the control unit and make sure the door sensing switch is

closed (either close the door or short the door sensing switch connector). Use the key unit matrix indicated on the control panel schematic and place

a jumper wire between the pins that 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.

G 4

G 3

G 2

G 1

[15] Procedure O: RELAY TEST

CARRY OUT 3D CHECKS.

Remove the outer case and check voltage between Pin No 9 of the 5-pin connector (A) and the common terminal of the relay RY1 on the control unit

with an A.C. voltmeter. The meter should indicate230 - 240 volts, if not check oven circuit.

Shut-off, Cook and Heater 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 or convection 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 defective.

RELAY SYMBOL

OPERATIONAL VOLTAGE

RY1

APPROX. 21.0V D.C.

RY2(COOK)

APPROX. 21.0V D.C.

RY3(HEATER)

APPROX. 20.0V D.C.

RY4

APPROX. 21.0V D.C.

RY5

APPROX. 21.0V D.C.

RY6

APPROX. 21.0V D.C.

CARRY OUT 4R CHECKS.

[16] Procedure P: PROCEDURES TO BE TAKEN WHEN THE FOIL PATTERN ON THE

PRINTED WIRING BOARD (PWB) IS OPEN

To protect the electronic circuits, this model is provided with a fine foil pattern added to the primary on the PWB, this foil pattern acts as a fuse. If the

foil pattern is open, follow the troubleshooting guide given below for repair.

Problem: POWER ON, indicator does not light up.

CARRY OUT 3D CHECKS.

STEPS

The rated voltage is not applied between Pin No. 9 of the 5-pin connector (A)

and the common terminal of the relay RY1.

G 5

G 6

G 7

STOP

REHEAT

LOW MIX