Sharp R-28STM Service Manual ▷ View online
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
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.
• 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
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
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
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
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
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 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)
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
TROUBLE SHOOTING PROCEDURES
Before overhauling a microwave oven, you should judge the breakdown and the cause correctly, then you can repair it with
corresponding ways. The overhauling must be proceed in order, any hasty conclusion is not recommendable, otherwise
overworking would be done when repair. The microwave oven may occur compound breakdown due to all kinds of different
reasons, thus, when overhaul, they all should be taken into consideration. Special attention must be given to the microwave
leakage and the electric insulation when examine because they may do harmful to the repairing staff.
Ⅰ
corresponding ways. The overhauling must be proceed in order, any hasty conclusion is not recommendable, otherwise
overworking would be done when repair. The microwave oven may occur compound breakdown due to all kinds of different
reasons, thus, when overhaul, they all should be taken into consideration. Special attention must be given to the microwave
leakage and the electric insulation when examine because they may do harmful to the repairing staff.
Ⅰ
.MEANS OF THE BREAKDOWN EXAMINING
How to examine a microwave oven with breakdown? A better means which demonstrated in practical operating are through
inspecting and listening. On the basis of large amounts of perceptual knowledge, you can judge and analysis the breakdown
quickly and correctly.
1. Inspection.
inspecting and listening. On the basis of large amounts of perceptual knowledge, you can judge and analysis the breakdown
quickly and correctly.
1. Inspection.
Inspect whether the oven shape is disordered and where is the disordered position, if any. It is normal if the outer case
disordered a little, but abnormal if the oven, the door disordered, the door hook broken, the door crooked, or there are too
much looseness between the door and the oven after the door is closed.
disordered a little, but abnormal if the oven, the door disordered, the door hook broken, the door crooked, or there are too
much looseness between the door and the oven after the door is closed.
2. Listening.
Listening to the voice of the oven operating and the noise of the fan after it conducted. Minor “wen wen” noise, cycling “kala”
noise and “shishi” noise should be consider as normal. But it is abnormal if the following noise occurred:
noise and “shishi” noise should be consider as normal. But it is abnormal if the following noise occurred:
(1) Sound “wenwen” noise.
(2) Long time “shishi” noise.
(3) Strike voice like “pipa pipa”.
(2) Long time “shishi” noise.
(3) Strike voice like “pipa pipa”.
Ⅱ
.SPOT EXAMINING STEPS OF THE MICROWAVE OVEN.
1. Examine the microwave insulating resistance.
Measure the insulating resistance with a multi meter or a mega ohmmeter. The value should not less than 2 mega ohm.
Otherwise, part examination should be taken at once. Such as checking whether the motor, the thermal cutout, the
transformer or the capacitor are electricity leaking.
Otherwise, part examination should be taken at once. Such as checking whether the motor, the thermal cutout, the
transformer or the capacitor are electricity leaking.
2. Examination of the resistance value of the microwave oven.
Close the door, set the time (the oven is at operating condition but the power plug haven’t been plugged in), measure the two
feet(L-N)of the power plug with Rx1 grade of a multimeter, the resistance value should be about 22 ohm.
If open circuit occurred, then you must check whether the
feet(L-N)of the power plug with Rx1 grade of a multimeter, the resistance value should be about 22 ohm.
If open circuit occurred, then you must check whether the
10 A fuse is broken、the primary winding of the transformer is open
circuit、the thermal cutout is open circuit or not, you must check whether the interlock device is put through or all the plugs
are connected well. If short circuit occurred, you should check whether the primary winding of the power transformer is short-
circuited or part short-circuited.
circuited or part short-circuited.
3. Examination of microwave leakage
Measure the microwave leakage with a microwave leakage Measure. Place a graduate of 275ml water at the middle of the
glass tray of the oven (FIG.5-1). Close the door, power set high, time set to 3 minutes, press the starting button to operate the
oven. After rectified the microwave leakage measure, measure around the door crack, those hole position of the window and
the air vent at four sides of the oven with the probe of the measure. When measure, the moving speed of the probe should
not exceed 2.5cm per second, and the measuring direction should be the same with the outing direction of the microwave
leakage (FIG.5-2).
When measuring, the ultimate value of microwave leakage of all the measured position should not exceed 1.0 mili watt/cm
glass tray of the oven (FIG.5-1). Close the door, power set high, time set to 3 minutes, press the starting button to operate the
oven. After rectified the microwave leakage measure, measure around the door crack, those hole position of the window and
the air vent at four sides of the oven with the probe of the measure. When measure, the moving speed of the probe should
not exceed 2.5cm per second, and the measuring direction should be the same with the outing direction of the microwave
leakage (FIG.5-2).
When measuring, the ultimate value of microwave leakage of all the measured position should not exceed 1.0 mili watt/cm
2
,
or should be considered as abnormal.
275ml
FIG.5-1
Glass tray
FIG.5-2
5-4
Click on the first or last page to see other R-28STM service manuals if exist.