Sharp R-820BK, Service Manual

Page: 15 / 48

13
R-820BK
R-820BW
TROUBLESHOOTING GUIDE
Never touch any part in the circuit with your hand or an uninsulated tool while the power supply is connected.
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 monitor fuse, check the monitor switch, relay (RY6),
primary interlock relay (RY2), door sensing switch and secondary interlock switch before replacing the
monitor fuse. If monitor fuse is replaced, the monitor switch must also be replaced. Use part FFS-
BA021WRK0 as an assembly.
IMPORTANT: Whenever troubleshooting is performed with the power supply cord disconnected. It may in, some cases,
be necessary to connect the power supply cord after the outer case has been removed, in this event,
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Disconnect the leads to the primary of the power transformer.
5. Ensure that the leads remain isolated from other components and oven chassis by using insulation tape.
6. After that procedure, reconnect the power supply cord.
When the testing is completed
1. Disconnect the power supply cord, and then remove outer case.
2. Open the door and block it open.
3. Discharge high voltage capacitor.
4. Reconnect the leads to the primary of the power transformer.
5. Reinstall the outer case (cabinet).
6. Reconnect the power supply cord after the outer case is installed.
7. Run the oven and check all functions.
BOTTOM HEATER
The bottom heater is located on the floor of the oven cavity
assembly. The bottom heater sends out heat to grill foods.
CONVECTION COOKING SYSTEM
This oven is designed with a hot air heating system where
food is not directly heated by the top heaters and the bottom
heater, but is heated by forced circulation of the hot air
produced by the top heaters and the bottom heater.
The air heated by the top heaters and the bottom heater 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 then enters
the inside of the oven through the vent holes provided on the
left side of the oven. Next, the hot air heats the food on the
turntable and leaves the oven cavity through the vent in the
center of the oven cavity rear wall.
Most of this hot air is reheated by the top heaters and the
bottom heater and passes through the convection passage
and enters the inside of the oven cavity again, in a continu-
ing cycle.
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 top heaters and the bottom heater
are de-energized. When the temperature inside the oven
cavity drops below the selected temperature, the top heat-
ers and the bottom heater 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 top heaters and
the bottom heater are de-energized and the convection fan
stops operating and the oven shuts off.