R-86STM (serv.man6). Function Of Important Components — Sharp Home Appliance Service Manual (repair manual)

Model
R-86STM (serv.man6)
Pages
2 Few pages! See other manuals at the bottom of the first or last page.
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113.86 KB
Type
PDF
Document
Service Manual
Brand
Device
Home Appliance / Microwave Oven / Function Of Important Components
File
r-86stm-sm6.pdf
Date

View Sharp R-86STM (serv.man6) Service Manual online

R86STM
6 – 1
R86STM
Service Manual
 
CHAPTER 6. 
FUNCTION OF IMPORTANT COMPONENTS
[1] DOOR OPEN MECHANISM
The door can be opened by pushing the door open button. When the
open button is pushed ,the open button push up the open lever and
then the open lever push up the latch head, , the latch head is moved
upward, and released from the latch hook now the door can be
opened.
Figure D-1. Door Open Mechanism
[2] SWITCH
1. MONITORED LATCH SWITCH
1. When the oven door is closed, the contacts (COM-NO) of the
switch must be closed. And the contacts (COM-NC) must be
opened.
2. When the oven door is opened, the contacts (COM-NO) of the
switch must be opened. And the contacts (COM-NC) must be
closed.
2. STOP SWITCH
1. When the oven door is closed, the contacts (COM-NO) of the
switch must be closed.
2. When the oven door is opened, the contacts (COM-NO) of switch
must be opened.
3. MONITOR SWITCH
The monitor switch is activated (the contacts opened) by the upper
latch head on the door while the door is closed. The switch is intended
to render the oven inoperative by means of blowing the fuse F8A when
the contacts of the monitored latch switch fail to open when the door is
opened.
Function
1. When the door is opened, the contacts (COM-NC) of monitor
switch close (to the ON condition) due to their being normally
closed and contacts (COM-NO) open. At this time the contacts
(COM-NO) of monitored latch switch is in the OFF condition (con-
tacts open) due to their being normally open contact switches.
2. As the door goes to a closed position, the monitor switch contacts
(COM-NC) are opened and contacts (COM-NO) closed and then
contacts (COM-NO) of monitored latch switch and stop switch are
closed.(On opening the door, each of these switches operate
inversely.)
3. If the door is opened and the monitored latch switch contacts
(COM-NO) fail to open, the fuse F8A blows immediately after clos-
ing of the monitor switch (COM-NC) contacts.
CAUTION: BEFORE REPLACING A BLOWN FUSE F8A, TEST THE
MONITORED LATCH SWITCH AND MONITOR SWITCH
FOR PROPER OPERATION. (REFER TO CHAPTER
“TEST PROCEDURE”).
[3] FUSE
1. FUSE 20A 250V
If the wire harness or electrical components are shortcircuited, this
fuse blows to prevent an electric shock or fire hazard.
2. FUSE F8A 250V
1. If the wire harness or electrical components are shortcircuited, this
fuse blows to prevent an electric shock or fire hazard.
2. The fuse also blows when the monitored latch switch remains
closed with the oven door open and when the monitor switch con-
tact (COM-NC) closes.
3. The fuse also blows when the asymmetric rectifier, H.V. rectifier,
H.V. wire harness, H.V. capacitor, magnetron or secondary winding
of high voltage transformer is shorted.
[4] TC TRANSFORMER
T/C transformer converts A.C. line voltage into low voltage to drive the
control unit.
[5] THERMAL CUT-OUT
1. THERMAL CUT-OUT 125
°C (MG)
This thermal cut-out protects the magnetron against overheat. If the
temperature goes up higher than 125
°C because the fan motor is
interrupted or the ventilation openings are blocked, the thermal cut-out
will open and line voltage to the high voltage transformer will cut off
and operation of the magnetron will be stopped. The defective thermal
cut-out must be replaced with a new one.
2. THERMAL CUT-OUT 145
°C (OVEN)
This thermal cut-out protects against overheating /fire inside the oven.
The cut-out contacts will open when temperatures exceed 145
°C.
When the cut-out cools itself down to the operating temperature of
115
°C, the contacts of the thermal cut-out will close again.
[6] ASYMMETRIC RECTIFIER
The asymmetric rectifier is solid state device that prevents current flow
is both directions. And it prevents the temperature rise of the high volt-
age transformer by blowing the fuse F8A when the high voltage recti-
fier is shorted.
The rated peak reverse voltage of D1 of the asymmetric rectifier is 6
KV. The rated peak reverse voltage of D2 of the asymmetric rectifier is
1.7 KV. D1 and D2 of the asymmetric rectifier or high voltage rectifier
are shorted when the each peak reverse voltage goes beyond the
each rated peak reverse voltage. (The process of the blowing the fuse
F8A.)
1. The high voltage rectifier is shorted by some fault when microwave
cooking or dual cooking.
LATCH
HEADS
LATCH HOOK
DOOR OPEN BUTTON
OPEN LEVER
DOOR
MONITOR SWITCH
MONITORED LATCH
SWITCH
STOP SWITCH
D2
D1
ASYMMETRIC
RECTIFIER
HIGH VOLTAGE
RECTIFIER
R86STM
6 – 2
2. The peak reverse voltage of D2 of the rectifier goes beyond the
rated peak reverse voltage 1.7 KV in the voltage doubler circuit.
3. D2 of the rectifier is shorted.
4. The large electric currents flow through the high voltage winding of
the high voltage transformer.
5. The large electric currents beyond 8A flow through the primary
winding of the high voltage transformer.
6. The fuse F2 F8A blows by the large electric currents.
7. The power supplying to the high voltage transformer is cut off.
[7] NOISE FILTER
The noise filter assembly prevents radio frequency interference that
might flow back in the power circuit.
[8] MOTOR
1. TURNTABLE MOTOR
The turntable motor rotates the turntable.
2. FAN MOTOR
The fan motor drives a blade which draws external cool air. This cool
air is directed through the air vanes surrounding the magnetron and
cools the magnetron. This air is channelled through the oven cavity to
remove steam and vapours given off from heating food. It is then
exhausted through the exhausting air vents of the oven cavity.
3. CONVECTION MOTOR
The convection motor drives the convection fan and provide the
heated air.
[9] HEATING ELEMENT
1. TOP GRILL HEATING ELEMENT
The grill heating element is provided to brown the food and is located
on the top of the oven cavity.
2. BOTTOM GRILL HEATING ELEMENT
The grill heating element is provided to brown the food and is located
at the base of the oven cavity.
[10] CONVECTION COOKING SYSTEM
°C, the fan motor remains rotat-
ing. Automatically the fan motor will be shut down at low temperature
(less than 105
°C).
Figure D-2. Convection Cooking System
[11] FIRE SENSING FEATURE
The oven will stop its operation when there is a fire in the oven cavity
in microwave cooking condition. 
LSI measures the voltage across the temperature measurement circuit
intermittently within 32-seconds time base since the oven is started in
microwave cooking condition. The oven will stop its operation when
the difference of the voltage is more than 0.781 volts in microwave
cooking condition.
1. Within a 32-seconds base, the thermistor is energized for 2 sec-
onds. At that time, the voltage across the temperature measure-
ment circuit is measured.
2. The oven carries out the procedure above again. If the second volt-
age is 0.781V higher than first voltage, LSI judges it as a fire in the
oven cavity and stop the oven.
3. When LSI judges it as a fire in the oven cavity, LSI will switch off the
relays to high voltage transformer and fan motor and LSI stops
countering down.
[12] OPEN JUDGE BY THERMISTOR
1. If the temperature of the thermistor does not rise to more than 40
°C
after 4 minutes and 15 seconds from when the oven is started in
convection, grill (top and bottom grills) or dual cooking mode, the
oven is turned off.
2. When the thermistor or the wire harness to the thermistor is
opened, the oven is turned off after 4 minutes and 15 seconds
because this condition is same as above.
Door
Oven Cavity
Grill Heating
Element
Bottom Grill
Heating Element
Convection
Passage
Cooling
Fan
Convection
Motor
Convection
Fan
Turntable
Insulation
Turntable
Motor
THERMISTOR
SENSING
VOLTAGE
ON
OFF
ON
OFF
30
32 (sec.)
Sensing the voltage across temperature measurement circuit.
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