Troubleshooting Guide - Sharp R-84ST Service Manual

CONVECTION COOKING SYSTEM
This oven is designed with a hot air heating system where
food is heated by forced circulation of the hot air produced by
the grill heaters.
The air heated by the grill heaters is circulated through the
convection passage provided on the outer casing of the oven
cavity by means of the convection fan which is driven by the
convection motor. It is then circulated inside the oven through
the vent holes provided on the back side of the oven. Next,
the hot air heats the food on the turntable and leaves the
oven cavity through the vent in the oven cavity rear wall.
In this way, the hot air circulates inside the oven cavity to
raise its temperature and, at the same time, comes into
contact with the food being cooked.
When the temperature inside the oven cavity reaches the
selected temperature, the heating elements are
de-energized. When the temperature inside the oven cavity
drops below the selected temperature, the heating elements
are energized again. In this way, the inside of the oven cavity
is maintained at approximately the selected temperature.
When the convection time reaches "0", the heating elements
are de-energized and the convection fan stops operating
and the oven shuts off. At the high temperature (more than
104˚C), the fan motor remains rotating. Automatically the fan
motor will be shut down at low temperature (less than
104˚C).
Door
Oven Cavity
Turntable
Motor
Insulator
Figure D-2. Convection Cooking System
When troubleshooting the microwave oven, it is helpful to follow the Sequence of Operation in performing the checks. Many
of the possible causes of trouble will require that a specific test be performed. These tests are given a procedure letter which
will be found in the "Test Procedure" section.
IMPORTANT: If the oven becomes inoperative because of a blown fuse F2 (F8A) in the monitored latch switch - monitor switch
circuit, check the monitored latch switch and monitor switch before replacing the fuse F2 (F8A).
FUNCTION OF IMPORTANT COMPONENTS
Grill Heating
Elements
Convection
Passage
Auxiliary
Fan
Convection
Motor
Convection
Fan
Turntable
Roller Stay
Bottom
Heater
Element

TROUBLESHOOTING GUIDE

R-84ST -
FIRE SENSING FEATURE
The oven will stop its operation when there is a fire in the oven
cavity in microwave cooking condition.
The LSI measures the voltage across the temperature meas-
urement circuit intermittently within a 32-second time base
after the oven is started in microwave cooking condition. The
oven will stop its operation when the difference of the voltage
is more than 0.781 volts in microwave cooking condition.
1. Within a 32-seconds base, the thermistor is energized for
2 seconds. At that time, the voltage across the temperature
measurement circuit is measured.
2. The oven carries out the procedure above again. If the
second voltage is 0.781V higher than first voltage, the LSI
judges it is a fire in the oven cavity and will stop the oven.
3. When the LSI judges it is a fire in the oven cavity, LSI will
switch off the relays to high voltage transformer and fan
motor and LSI stops countring down.
THERMISTOR
ON
OFF
ON
Sensing
Voltage
OFF
Sensing the voltage across temperature measurement circuit.
OPEN JUDGE BY THERMISTOR
1. If the temperature of the thermistor does not rise to more
than 40˚C after 4 minutes and 15 seconds from when the
oven is started in convection, grill (top and bottom grills) or
dual cooking mode, the oven is turned off.
2. When the thermistor or the wire harness to the thermistor
is opened, the oven is turned off after 4 minutes and 15
seconds because this condition is same as above.
13
30 32 (sec.)