DOWNLOAD Sharp R-822STM Service Manual ↓ Size: 1.63 MB | Pages: 23 in PDF or view online for FREE

Model
R-822STM
Pages
23
Size
1.63 MB
Type
PDF
Document
Service Manual
Brand
Device
Home Appliance / Microwave Oven
File
r-822stm.pdf
Date

Sharp R-822STM Service Manual ▷ View online

 
 
 
CIRCUIT DESCRIPTION
 
 
 
4-2 
GENERAL DETAILS
• The low voltage transformer supplies the necessary
voltage to the micom controller when power cord is
plugged in.
• When the door is closed, the primary switch is ON, the
secondary switch is ON, and the monitor switch opens
(contact COM and NO).
WHEN SELECTING COOKING POWER
LEVEL AND TIME
• The micom controller memorizes the function you set.
• The time you set appears in the display window.
• Each indicator light turns on to indicate that the stage
has been set.
WHEN TOUCHING THE START PAD
• The coil of the relay is energized by the micom
controller.
• Power input is supplied to the high voltage transformer
through the fuse to the primary switch and relay 2.
• Turntable rotates.
• The fan motor rotates and cools the magnetron by
blowing the air (coming from the intake on the
baseplate)
• The air is also directed into the oven to exhaust the
vapor in the oven through the upper plate.
• Cooking time starts counting down.
• 3.2 volts AC is generated from the filament winding of
the high voltage transformer. This 3.2 volts is applied
to the magnetron to heat the magnetron filament
through two noise preventing choke coils.
• A high voltage of approximately 2100 volts AC is
generated in the secondary of the high voltage
transformer which is increased by the action of the high
voltage diode and charging of the high voltage
capacitor.
• The negative 4,000 Volts DC is applied to the filament
of the magnetron.
WHEN THE OVEN IS SET AT ANY LEVEL
EXCEPT MAXIMUM.
• The micom controller controls the ON-OFF time of relay
2 by the applied signal to vary the average output 
power of microwave oven as POWER LEVEL.
WHEN THE DOOR IS OPENED DURING
COOKING
• Both the primary switch and relay 2 are cut off primary
winding voltage of the high voltage transformer.
• ON-OFF of relay 2 is coupled electrically with opening
and closing of the secondary switch.
• When the door is opened, the secondary switch is
opened and when the door is closed, the secondary
switch is closed.
• The cooking time stops counting down.
• Relay stops functioning.
• As the door is opened, if the contact of primary switch
and relay 2 and/or secondary switch fails to open, the
fuse opens due to the large current surge caused by
the monitor switch activation, which in turn stops
magnetron oscillation.
WHEN TOUCHING THE START KEY
WITH THE GRILL COOKING FUNCTION
SELECTED
• The contacts of the primary switch and the secondary
switch close the circuit.
• A.C.voltage is applied to the grill heater through grill
thermostat as shown by the solid line.
• Turntable rotates.
• The fan motor rotates.
• The air is also directed into the oven to exhaust the
vapor in the oven through the base plate and upper
plate.
L
N
GRILL
THERMOSTAT
GRILL
HEATER
L
G -Y
N
E
TOP HEATER RELAY 
L
FUSE
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
SWITCH
N
MONITOR
SWITCH
PRIMARY
MONITOR
SWITCH
L
FUSE
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
PRIMARY
SWITCH
N
TRANS-
FORMER
 
 
 
SERVICE INFORMATION 
TOOLS AND MEASURING INSTRUMENTS
 
NECESSARY TOOLS 
Tools normally used for TV servicing are sufficient. 
Standard tools are listed below. 
• Diagonal pliers 
• Long nose pliers 
• Phillips screwdriver 
• Flat blade screwdriver 
• Wrench (size 5mm) 
• Nutdriver (size 5mm) 
• Adjustable wrench 
• Soldering iron 
• Solder 
• Vinyl insulation tape 
• Polishing cloth 
 
 
MICROWAVE LEAKAGE TEST
 
CAUTIONS 
• Be sure to check microwave leakage prior to 
servicing the oven if the oven is operative prior to 
servicing. 
• The service personnel should inform the 
manufacture importer, or assembler of any certified 
oven unit found to have a microwave emission 
level in excess of 5 mW/cm
2
 
and should repair any 
unit found to have excessive emission levels at no cost 
to the owner and should ascertain the cause of the 
excessive leakage. The service personnel should 
instruct the owner not to use the unit until the oven has 
been brought into compliance. 
• If the oven operates with the door open, the service 
personnel should: 
- Tell the user not to operate the oven. 
- Contact the manufacturer. 
• The service personnel should check all surface and 
vent openings for microwave leakage. 
• Check for microwave leakage after every servicing. The 
power density of the microwave radiation leakage 
emitted by the microwave oven should not exceed 
5 mW/cm
2
. Always start measuring of an unknown field 
to assure safety for operating personnel from radiation 
leakage. 
 
NECESSARY MEASURING 
INSTRUMENTS 
• TESTER(VOLTS-DC, AC., Ohmmeter) 
• Microwave survey meter 
- Holaday HI-1710(A) 
- Narda 8100 
8200 
• Inch scale 
• 600 cc non conductive material beaker (glass or 
plastic), inside diameter: approx. 8.5 cm(3
1/2 
in.) 
• Cylindrical and made of borosilicate glass vessel. 
max. thickness: 3 mm 
outside diameter: approx. 190mm 
height: approx. 90mm 
• Glass thermometer: 100°C or 212°F (1 deg scale) 
MEASURING MICROWAVE ENERGY 
LEAKAGE 
• Pour 275±15 cc of 20±5°C(68±9°F) water in a 
beaker 
which is graduated to 600 cc, and place the beaker 
on the center of the turntable. 
• Set the energy leakage monitor to 2,450 MHz and 
use it following the manufacturer's recommended 
test procedure to assure correct result. 
• When measuring the leakage, always use the 2-
inch (5 cm) spacer supplied with the probe. 
• Operate the oven at its maximum output. 
• Measure the microwave radiation using and 
electromagnetic radiation monitor by holding the 
probe perpendicular to the surface being measured 
Move probe along shaded area 
Probe scanning speed: Less than 2.5 cm/sec 
 
5-1 
 
 
 
 
MEASUREMENT WITH OUTER CASE 
REMOVED 
• When you replace the magnetron, measure for 
microwave energy leakage before the outer case is 
installed and after all necessary components are 
replaced or adjusted. 
Special care should be taken in measuring the 
following parts. 
- Around the magnetron 
- The 
waveguide 
 
 
 
 
 
 
 
 
MEASUREMENT WITH A FULLY 
ASSEMBLED OVEN 
• After all components, including the outer case, are fully 
assembled, measure for microwave energy leakage 
around the door viewing window, the exhaust opening, 
and air inlet openings. 
• Microwave energy leakage must not exceed the values 
prescribed below. 
NOTE: Leakage with the outer case removed less than 
3 mW/cm
2
. Leakage for a fully assembled 
oven (Before the latch switch (primary) is 
interrupted) with the door in a slightly opened 
position-less than 1 mW/cm
2
 
 
 
 
 
 
 
 
 
 
 
 
 
 
NOTES WHEN MEASURING
 
• Do not exceed meter full scale deflection. 
• The test probe must be removed no faster than 
1 inch/sec (2.5 cm/sec)
 
along the shaded area, 
otherwise a false reading may result. 
• The test probe must be held with the grip portion of 
the 
handle. 
A false reading may result if the operator's hand is 
between the handle and the probe. 
• When testing near a corner of the door, keep the 
probe 
perpendicular to the surface making sure the probe 
horizontally along the oven surface, this may possibly 
cause probe damage. 
RECORD KEEPING AND NOTIFICATION 
AFTER MEASUREMENT 
• After adjustment and repair of any microwave energy 
interruption or microwave energy blocking device, 
record the measured values for future reference. Also 
enter the information on the service invoice. 
• The microwave energy leakage should not be more 
than 1.0 mW/cm
2
. after determining that all parts are in 
good condition, functioning properly and genuine 
replacement parts which are listed in this manual have 
been used. 
• At least once a year, have the electromagnetic energy 
leakage monitor checked for calibration by its 
WARNING : AVOID CONTACTING ANY
HIGH VOLTAGE PARTS 
(Magnetron, H.V. Transformer, 
H.V. Capacitor, H.V. Cable Ass’y, 
H.V. Fuse)
 
5-2 
 
 
 
MEASUREMENT OF MICROWAVE POWER OUTPUT 
 
• Microwave power output measurement is made with 
the microwave oven supplied at its rated voltage and 
operated at its maximum microwave power setting with 
a load of (1000±5) g of potable water. 
• The water is contained in a cylindrical borosilicate glass 
vessel having a maximum material thickness of 3 mm 
and an outside diameter of approximately 190mm. 
• The oven and the empty vessel are at ambient 
temperature prior to the start of the test. 
• The initial temperature (T1) of the water is (10±2)°C It 
is measured immediately before the water is added to 
the vessel. After addition of the water to the vessel, 
the load is immediately placed on the center of the 
turntable which is in the lowest position and the 
microwave power switched on. 
• The time T for the temperature of the water to rise by a 
value . T of (10±2)°K is measured, where T is the time 
in seconds and .T is the temperature rise. The initial 
and final water temperatures are selected so that the 
maximum difference between the final water 
temperature and the ambient temperature is
 
2°K. 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
• The microwave power output P in watts is 
calculated 
approximately from the following formula : 
P=4187 x (△T)/T 
is measured while the microwave generator is 
operating at full power. Magnetron filament heat-up 
time is not included. (about 3 sec) 
• The water is stirred to equalize temperature 
throughout 
the vessel, prior to measuring the final water 
temperature. 
• Stirring devices and measuring instruments are 
selected in order to minimize addition or removal of 
heat. 
5-3 
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