R-741M (serv.man2) - Sharp Home Appliance Service Manual (repair manual). Page 6

6

741M -

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 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".

See NOTE : 2.

(CARRY OUT 3D CHECKS BEFORE REPAIR)

NOTE : 1

*At the time of these repairs, make a
visual inspection of the varistor for
burning damage and examine the
transformer with tester for the pres-
ence of layer short-circuit (check pri-
mary coil resistance). If any abnor-
mal condition is detected, replace
the defective parts.

NOTE : 2

The hole "C" is not prepared for the
coil on this PWB. So, insert the coil
instead of J1 at first. Then solder the
one lead wire of the coil at "d". And
solder the other lead wire of the coil
at the Pin No.1 of the connector CN-
A.

CARRY OUT 4R CHECKS.

VRS1

D20

WH - 3

A

5

1

AC

CN - A

OL/FM
/TTM

(J1)

D21

RY1

See NOTE : 2
Lead wire of coil

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

APPROX. 24.0V D.C.

Oven lamp / Turntable motor / Cooling fan motor

RY2

APPROX. 18.0V D.C.

Grill heater

RY3

APPROX. 18.0V D.C.

High voltage transformer