Sharp r-8580 Description And Function Of Components, Thermistor, Oven Thermal Cut-Out, Functions

R -8580

DESCRIPTION AND FUNCTION OF COMPONENTS

THERMISTOR

The thermistor is a negative temperature coefficient type. The temperature in the oven cavity is detected through the resistance of the thermistor, and then the CPU unit causes the heater relay to operate, thus the current to the convection heater is turned ON/OFF.

OVEN THERMAL CUT-OUT

The oven thermal cut-out located on the bottom side of the thermal protection plate is designed to prevent damage to the convection heater unit if an overheated condition develops in the tube due to cooling fan fail- ure, obstructed air ducts, dirty or blocked air intake, etc. Under normal operation, the oven thermal cut-out re- mains closed. However, when abnormally high tem- peratures are reached within the heater unit, the oven thermal cut-out will open, causing the oven to shut down.

When the oven has cooled temperature, the oven thermal cut-out closes.

MONITOR SWITCH

The monitor switch is mounted on the upper latch hook. It is activated (the contacts opened) by the up- per latch head when the door is closed. The switch is intended to render the oven inoperative by means of blowning the fuse when the contacts of the common and normal open contacts of upper latch switch fail to open when the door is opened.

Functions:

1.When the door is opened, the monitor switch con- tacts close (to the ON condition) due to their being normally closed. At this time the the common and normal open contacts of upper latch switch are in

the OFF condition (contacts open) due to their being normally open contacts switch.

2.As the door goes to a closed position, the monitor switch contacts are first opened and then the common and normal open contacts of upper latch switch close. (On opening the door, each of these switches operate inversely.)

3.If the door is opened during cooking, and the common and normal open contacts of upper latch switch fail to open, the monitor fuse blows simul- taneously with closing of the monitor switch con- tacts.

CAUTION:BEFORE REPLACING A BLOWN FUSE TEST THE UPPER LATCH SWITCH AND

MONITOR SWITCH FOR PROPER

OPERATION.(REFER TO CHAPTER “TEST PROCEDURE”).

AFTER REPLACING FUSE ALSO REPLACE MONITOR SWITCH.

STOP SWITCH

The stop switch is activated by the lower latch head. When the door is opened while the oven is in cook cycle, the stop switch contacts open to de-energize the relay(RY-l,RY-2,RY-3,RY-4,RY-5).

Then the cook cycle is stopped.

UPPER AND LOWER LATCH SWITCHES

The lower latch switch is mounted in the lower latch hook and the upper latch switch is mounted in the upper latch hook. They are activated by the latch heads on the door. When the door is opened, the switches interrupt the’crrcuit to all components except CPU unit and relay unit and oven lamp. A cook cycle cannot take place until the door is firmly closed thereby activating both interlock switches.

P

’UPPER

A LATCH HOOK

Figure D-l. Upper Latch Switch, Lower Latch

Switch, Monitor Switch and Stop Switch