R-555. R555 - Sharp Home Appliance Service Manual (repair manual). Page 13

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Remove the outer case and check voltage between Pin No 1 of the 2-pin connector (A) and the normal
open terminal of the relay RY1 on the power unit with an A.C. voltmeter. The meter should indicate
230 - 240 volts, if not check oven  circuit.

RY1 and RY2 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 defective.

RELAY SYMBOL

OPERATIONAL VOLTAGE

CONNECTED COMPONENTS

RY1

APPROX. 12V D.C.

Oven lamp / Turntable motor / Cooling fan motor

RY2

APPROX. 12V D.C.

Power transformer

CARRY OUT 4R CHECKS.

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 2nd. Interlock Relay Control Switch operates properly; that is
the contacts are closed when the door is closed 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 unit 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 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 key pad is at fault.

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.

G 9

G 8

G 7

G 6

G 5

G 4

G 3

G 2

G 1

G10

G11

G12

G13

G14