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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

 
 
 
 
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 
 
 
 
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. 
.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. 
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. 
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: 
(1)  Sound “wenwen” noise. 
(2)  Long time “shishi” noise. 
(3)  Strike voice like “pipa pipa”. 
.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. 
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
 
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. 
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
2
or should be considered as abnormal. 
 
 
 
 
         
                                                                                                 
 
 
 
 
 
 
 
 
 
 
275ml
 
FIG.5-1 
Glass tray 
FIG.5-2 
 
5-4
 
 
 
 
4.  Examine when the oven at operating, but the food can’t be heated 
Pull out the power plug, take off the outer case, discharge the capacitor, measure the resistance value of the primary winding and 
the secondary winding of the transformer with a multi meter
 
(FIG.5-3 and FIG.5-4). The resistance value of the primary winding 
should be about 2.2 ohm, the secondary winding should be about 130 ohm, otherwise, it indicates the transformer has broken, 
and should be replaced by a new one. 
If the transformer is normal, then the high voltage capacitor should be checked. Pull out the connecting plug of the capacitor, 
and measure it with Rx1 grade of a multi meter, the two rod of the multi meter connect the two polarity of the capacitor. When 
they just connected, the reading of the multi meter should be zero, then enlarge to nine mega ohm slowly. Change the rod to 
different polarity, the reading repeat from zero to 9 mega ohm (FIG.5-5),it means the capacitor is normal. If the indicator of the 
multi meter can’t point out from zero to 9  mega ohm, it indicates the high voltage capacitor has broken, and should be 
replaced by a new one. 
 
 
 
 
 
 
 
 
 
If it is normal between the two pole of the capacitor, then the insulation between the capacitor pole and the cabinet (FIG.5-6) 
should be checked. 
If the resistance value between the capacitor pole and the cabinet is “∞”,the capacitor is normal. Then check the earth of the 
magnetron’s two filament to see whether they are short-circuited (FIG.5-7).If they are short-circuited and the filament strikes 
the shell of the magnetron, it indicates the magnetron has broken, and should be replaced by a new, same model one. 
If there is no problem with the magnetron, check the high voltage diode then. Measure the diode with Rx10k grade of a multi 
meter, the “-” rod end of the multi meter connect the cathode of diode, the “+ “ rod end of the multi meter connect the anode of 
the diode(FIG.5-8).The multi meter reading should be about 150 thousand ohm. Then change the rod to different 
electrode(FIG.5-9), the reading should be “∞”.If the reading is very small, and near to short circuit, it indicates the high 
voltage diode has been punctured, and should be replaced by a new one. 
If high voltage diode is also normal, then test the pilot switch(FIG.5-10). Pull out the two plugs of the switch, Measure it with 
the Rx1 grade of a multi meter, the two rod connect the plug of the switch, the resistance value should be “∞”.Then press 
down the pilot switch with a screwdriver, if the reading of the multi meter pointed to zero, it indicates the pilot switch has 
broken, and should replace it with a new, same model one.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
FIG.5-7 
5-5 
FIG5-6 
 
FIG5-5 
 
FIG.5-8 
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