R-753. Text - Sharp Home Appliance Service Manual (repair manual). Page 7

6

753M -

NOTE: *At the time of these repairs, make a

visual inspection of the varistor for burn-
ing damage and examine the transformer
with tester for the presence of layer short-
circuit (check primary coil resistance). If
any abnormal condition is detected, re-
place the defective parts.

CARRY OUT 4R CHECKS.

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

OCCURANCE

CAUSE OR CORRECTION

1

The rated AC voltage is not present at

Check supply voltage and oven power cord.

POWER terminal of CPU connector (CN-A).

2

The rated AC voltage is present at primary

Low voltage transformer or secondary circuit defective.

side of low voltage transformer.

Check and repair.

3

Only pattern at "a" is broken.

*Insert jumper wire J1 and solder.

(CARRY OUT 3D CHECKS BEFORE REPAIR)

4

Pattern at "a" and "b" are broken.

*Insert the coil RCILF2003YAZZ between "c" and "d".

(CARRY OUT 3D CHECKS BEFORE REPAIR)

1. CARRY OUT 3D CHECKS.
2. Disconnect the leads from the primary of the high voltage transformer. Make sure that the leads remain

isolated from other oven components and chassis. (Use insulation tape if necessary.)

3. Close the door.
4. Reconnect the supply.
5. Check the voltage between Pin Nos. 1 and 3 of the 3 pin connector (A) on the control unit with an A.C.

voltmeter. The meter should indicate 230-240 volts, if not check oven circuit.

6. RY1, RY2 and RY3 TEST
   These are operated by D.C. voltage. Check voltage at the relay coil with a D.C. voltmeter during the

microwave cooking operation, grill cooking or dual grill 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

CONNECTED COMPONENTS

RY1

APPROX. 18.0V D.C.

Oven lamp / Turntable motor / Cooling fan motor

RY2

APPROX. 24.0V D.C.

Grill heating element

RY3

APPROX. 18.0V D.C.

High voltage transformer

CN - A

AC

31

VRS1

(J1)