Sharp R-1500AT Service Manual Download Page 11

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R1500AT

4 – 2

[2] DESCRIPTION AND FUNCTION OF COMPONENTS

1. DOOR OPEN MECHANISM

1. The handle lever is pulled.

2. The upper and lower latch heads are lifted up by the linked latch

lever.

3. The latch lever is lifted up by the handle lever.

4. Now both latch heads are lifted up, so they can be released from

the latch hook.

5. Now the door can be opened.

Figure D-1. Door Open Mechanism

2. DOOR SENSING SWITCH: SW5

The door sensing switch is activated by the latch head of the door and
switch lever C. When the door is opened, the contacts of the switch
open and interrupt the circuit to the coils of the primary interlock relay.
The contacts of the primary relay then open and interrupt the circuit to
the primary winding of the power transformers T1, T2.

3. SECONDARY INTERLOCK SWITCHES: SW1, SW2

The secondary interlock switches SW1, SW2 are activated by the
upper latch head of the door and switch lever B. When the door is
opened, the contacts (COM-NO) of the switch open and interrupt the
circuit to the primary winding of the power transformers T1, T2. When
the door is opened, the contacts (COM-NC) of the switch SW1 close
and the line voltage is supplied to the switching power supply unit. At
the same time, the contacts of relay RY4 are closed.

4. MONITOR SWITCHES: SW3, SW4

The monitor switches SW3, SW4 are mounted in the upper position of
the latch hook. The monitor switches are activated by the upper latch
head of the door and switch lever A. When the door is opened, the
contacts of the monitor switches close. Monitor switch SW3 is
intended to render the oven inoperative by means of blowing the weak
point (F1), when the contacts of the primary interlock relay and sec-
ondary interlock switch SW1 fail to open when the door is opened.
Monitor switch SW4 is intended to render the oven inoperative by
means of blowing the weak point (F2), when the contacts of the pri-
mary interlock relay and secondary interlock switch SW2 fail to open
when the door is opened.

Functions:

With the door shut, the contacts of the door sensing switch SW5 and
the secondary interlock switches SW1, SW2 are closed and the con-
tacts of the monitor switches SW3, SW4 are open.

1. When the door is opened, the contact of the door sensing switch

SW5 and secondary interlock switches SW1, SW2 are opened first,
then the contact of the monitor switches SW3, SW4 are closed.

2. As the door goes to a closed position, the contacts of the monitor

switches SW3, SW4 are opened first, then the contacts of the door
sensing switch SW5 and the secondary interlock switches SW1,
SW2 close.

3. If the door is opened, and the contacts of the primary interlock relay

RY1 and secondary interlock switch of the same circuit fail to open,
the weak point blows simultaneously with closing of the monitor
switch contacts of that circuit.

CAUTION: BEFORE REPLACING A BLOWN FUSES F8 (F1, F2)

TEST THE DOOR SENSING SWITCH SW5, PRIMARY
INTERLOCK RELAY RY1, SECONDARY INTERLOCK
SWITCHES SW1, SW2, DOOR SENSING SWITCH SW5
AND MONITOR SWITCHES SW3, SW4 FOR PROPER
OPERATION. (REFER TO CHAPTER “TEST PROCE-
DURE”).

5. WEAK POINT: F1, F2

1. The weak point blows when the contacts (COM-NO) of the primary

interlock relay (RY1) and secondary interlock switch SW1 or SW2
remain closed with the oven door open and when the monitor
switch (SW3 or SW4) closes.

2. If the wire harness or electrical components are short-circuited, this

weak point (F1, F2) blows to prevent an electric shock or fire haz-
ard.

3. The weak point also blows when the asymmetric rectifier, H.V. rec-

tifier, H.V. wire harness, H.V. capacitor, magnetron or secondary
winding of power transformer is shorted.

6. MAGNETRON TEMPERATURE FUSES: TF1, TF2

The temperature fuses TF1, TF2 located on the top of the upper and
lower waveguide, are designed to prevent damage to the magnetrons
MG1, MG2. If an over heated condition develops in the tube due to
blower motor failure, obstructed air ducts, dirty or blocked air intake,
etc., the circuit to the magnetrons are interrupted. Under normal oper-
ation, the temperature fuses remains closed. However, when abnor-
mally high temperatures are generated within the magnetron, the
temperature fuse will open at 302

F (150

C) causing the microwave

energy to stop. The defective temperature fuse must be replaced with
new rated one.

7. OVEN TEMPERATURE FUSE: TF3

The temperature fuse, located on the side of the exhaust duct assem-
bly, is designed to prevent damage to the oven by fire. If the food load
is overcooked, by either error in cook time or defect in the control unit,
the temperature fuse will open. Under normal operation, the oven tem-
perature fuse remains closed. However, when abnormally high tem-
peratures are generated within the oven cavity, the oven temperature
fuse will open at 248

F (120

C), causing the oven to shut down. The

defective temperature fuse must be replaced with new rated one.

8. EXHAUST THERMISTOR

The exhaust thermistor is located on the side of the exhaust duct
assembly. The temperature in the exhaust duct is detected through the
resistance of the thermistor. If the temperature is high, the control
panel will display”EE7” and the oven will stop to avoid overheating and
catching fire. If the thermistor is open, the control panel will display
“EE8” and the oven will stop.

9. MAGNETRON THERMISTOR: TH

The thermistor is a negative temperature coefficient type. The air tem-
perature around the upper and lower magnetrons is detected through
the resistance of the thermistor. If the temperature is high, the control
panel will display “EE7” and the oven will stop to protect the magne-
trons against overheat. If the magnetron thermistor is open, the control
panel will display “EE8” and the oven will stop.

Latch hook

Latch

lever

SW4: Monitor switch

Secondary

interlock switch

Secondary

interlock switch

Door sensing

switch

SW3: Monitor switch

Switch lever A