Sharp R-82STM-A Service Manual ▷ View online
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
Ⅲ
.REPAIRING METHOD OF SEVERAL BREAKDOWN
1. Repair when there occurred large amounts microwave leakage. There are many factors, which may cause microwave leaking.
Following mentioned may be the main cause of microwave leakage:
(1) The door deformed, the hinge loosed or damaged that caused the door can not close tightly.
(2) The door pressing cover or the embed piece damaged or come off.
(3) Obvious damage or uneven of the oven.
(4) There are filth between the door and the oven.
(5) The door and the oven are serious loosed after the door closed.
(6) The crack of the door shielding net cover.
Before repairing, check whether the above listed point are existed, if not, you can start the microwave oven. Place a
graduate of about 275ml water at the middle of the glass tray, close the door, time set at 3 minutes, power at high,
makes the oven operating in normal. Rectify the microwave leakage measure, measure the amount of the microwave
leakage around the oven with its probe. If there are places which the leakage exceed the standard requirement, then
repair them accordingly. If the leakage amount exceed 1.0 mW/cm
2
at the left door crack, then pull out the power plug,
take down the outer case, adjust the screws of the hinge to less the gap between the door and the oven. Then measure
again, the leakage amount should less than 1.0 mW/cm
2
. Generally, it should be controlled below 0.8 mill watt/cm
2
with
some allowance.
If the leakage occurred at the right door crack, adjust the screws that fix the interlock holder and the hook. If the leakage
is on the larger side at the right-above of the oven, then adjust the upper screw. Loosen out the screw, push the door
close to the oven to hook the door hook with the plastic parts, then tighten the screw again. If the leakage is larger at
the right-below, then adjust the lower screw. Loosen the screw, push the door close to the oven to hook the door hook
with the switch holder tightly, then tighten the screw again, and open and close the door repeatedly to check whether the
door can operate flexibly, whether the hook and the switch are in their normal position. If it is not in position, then adjust
the door hook and the switch holder the loose between the door and the oven, then measure the leakage with
microwave leakage measure again.
If there still exist microwave leakage, measure near the magnetron with the probe of the microwave leakage measure. If
the leakage is larger, the oven should be turned off and check whether the 2 or 4 screws which fix the magnetron have
been loosed, if loosed, twist them tightly with socket wrench. If the screws are fixedly, then the magnetron should be
take down to check the copper filament weaved washer of the magnetron has been placed well or whether the wave
guide housing coupling has been oxidized or have lacquer on it. If do have, scrape the oxidized layer or the lacquer off,
when fix the magnetron, the copper filament weaved washer must be placed well, the screws must be twist tightly. Then
turn on the oven and measure again until it complies with the requirement. If the microwave leakage is larger at those
hole position of the window board, the oven should be turned off to inspect whether there are crack among them. If
several holes formed a crack, it would enlarge the microwave leakage. If that is the case, it indicates the door has
broken, and should be replaced with a new door.
5-6
FIG.5-9
FIG5.10
2. Means of repair when the oven can heat, but the turntable glass can’t move
Firstly, check whether the turntable holder is placed correctly. If it is correct, then pull out the power plug and take down the
turntable combination, measure the resistance value of the turntable motor with Rx1k grade of a multi meter If it is open-
circuited, it indicates the turntable motor has broken, and should be replaced by a new, same model one. If the resistance
value is between 15-22k,it indicates the turntable motor is normal, then check the connecting shaft weave. If the plastic that
the shaft insert in has broken, a new shaft weave should replace it.
3. Repair when the oven can heat, but the lamp is not on.
Pull out the power plug, take down the outer case and discharge the capacitor.
Pull out the two terminal plugs of the lamp, measure the two plugs of the lamp with the Rx100 grade of a multi meter. If it is
open-circuited, it indicates the lamp has broken, and should be replaced by a same model one.
4. Means of repair when the oven stop working after several minutes operating
The phenomenon indicated the thermal cutout is playing its protective role, and you should check whether the fan is working
in normal. Turn off the oven, pull out the power plug, take down the outer case, discharge the capacitor, then turn the fan with
hand to see whether it is moving flexibly. If not, it indicates that the oil bearing of the fan motor has run off the oil, and should
take down the fan combination to repair the motor. Loosen the two screws which fix the bearing out the shaft and the bearing,
and rinse them with kerosene (ATTENTION: The bearing can only be wiped with a silk which moistened with kerosene rather
than be washed in the kerosene because there are felt on it. If the felt are soaked with kerosene, then the engine oil can not
be sucked up.).After the bearing being cleaned, the felt should be refueled fully with engine oil(for when the oven is operating,
the engine oil empty into the oil bearing slowly).Fix the bearing cover with two screws, turn the fan around till it can move
flexibly. Than install them to the oven, and plug in the two terminal plugs.
If the fan can move flexibly, then the winding of the fan motor should be examined. Measure the winding with Rx100 grade of
a multi meter, if it is open-circuited, it indicates the winding of the fan motor has broken, and should be replaced by a new,
same model one.
5-7
MOTOR TEST PROCEDURE
COMPONENTS TEST
PROCEDURE
RESULTS
Fan Motor
(Wire leads removed)
Measure the resistance.
(Ohm-meter scale:R×100)
(Ohm-meter scale:R×100)
Normal:Approx. 47Ω
Abnormal:
∞
or Several Ω
Turntable Motor
(Wire leads removed)
Measure the resistance.
(Ohm-meter scale:R×1000)
(Ohm-meter scale:R×1000)
Normal:Approx. 3.2kΩ
Abnormal:
∞
or Several Ω
NOTE:
z A MICROWAVE LEAKGE TEST MUST ALWAYS BE PERFORMED WHEN THE UNIT IS
SERVICED FOR ANY REASON.
z MAKE SURE THE WIRE LEADS ARE IN THE CORRECT POSITION.
z WHEN REMOVING THE WIRE LEADS FROM THE PARTS,BE SURE TO GRASP THE
z WHEN REMOVING THE WIRE LEADS FROM THE PARTS,BE SURE TO GRASP THE
CONNECTOR ,NOT THE WIRES.
5-8
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