Read Sharp R-27STMA (serv.man5) Service Manual online
R27STMA
5 – 1
R27STMA
Service Manual
CHAPTER 5.
OPERATION SEQUENCE
[1] OFF CONDITION
1. When the oven is plugged in with the door closed, the line voltage
is supplied to the noise filter. And the display shows nothing.
2. When the door is opened with plugged in, the contacts (COM-NC)
of the secondary interlock switch is closed. And the line voltage is
supplied to the T/C transformer of the control unit. Then the con-
tacts of the relay RY-6 are closed. And the contacts of the relay RY-
5 are closed and the oven lamp is turned on. The display shows “
.0”.
supplied to the T/C transformer of the control unit. Then the con-
tacts of the relay RY-6 are closed. And the contacts of the relay RY-
5 are closed and the oven lamp is turned on. The display shows “
.0”.
3. When the door is closed, the contacts (COM-NC) of the secondary
interlock switch are opened. Because the contacts of the relay RY-6
have been closed, the line voltage is kept supplying to the T/C
transformer of the control unit. But the contacts of the relay RY-5
are opened and the oven lamp is turned off.
have been closed, the line voltage is kept supplying to the T/C
transformer of the control unit. But the contacts of the relay RY-5
are opened and the oven lamp is turned off.
NOTE: Energy save mode
1) If the oven has not been used for 3 minutes or more, the
contacts of the relay RY-6 will be opened and the control
unit will not be energized. Open and close the door, the
control unit will resume.
unit will not be energized. Open and close the door, the
control unit will resume.
IMPORTANT
When the oven door is closed, the monitor switch contacts (COM-NC)
must be open.
must be open.
[2] MICROWAVE COOKING CONDITION
1. HIGH COOKING
Enter a desired cooking time by rotating the TIME/WEIGHT knob and
start the oven with pressing START button.
start the oven with pressing START button.
Function sequence
Figure O-2 on page 14-1
1. Rated voltage is supplied to the primary winding of the high voltage
transformer. The voltage is converted to about 3.3 volts A.C. output
on the filament winding and high voltage of approximately 2000
volts A.C. on the secondary winding.
on the filament winding and high voltage of approximately 2000
volts A.C. on the secondary winding.
2. The filament winding voltage (3.3 volts) heats the magnetron fila-
ment and the high voltage (2000 volts) is sent to the voltage dou-
bling circuit, where it is doubled to negative voltage of
approximately 4000 volts D.C..
bling circuit, where it is doubled to negative voltage of
approximately 4000 volts D.C..
3. The 2450 MHz microwave energy produced in the magnetron gen-
erates a wave length of 12.24cm. This energy is channelled
through the waveguide (transport channel) into the oven cavity,
where the food is placed to be cooked.
through the waveguide (transport channel) into the oven cavity,
where the food is placed to be cooked.
4. When the cooking time is up, a signal tone is heard and the relays
(RY5+RY2) go back to their home position. The circuits to the oven
lamp, high voltage transformer, fan motor and turntable motor are
cut off.
lamp, high voltage transformer, fan motor and turntable motor are
cut off.
5. When the door is opened during a cook cycle, the switches come to
the following condition
The circuits to the high voltage transformer, fan motor, turntable motor
are cut off when the secondary interlock switch and door sensing
switch are made open. The oven lamp is turned on.
are cut off when the secondary interlock switch and door sensing
switch are made open. The oven lamp is turned on.
6. MONITOR SWITCH CIRCUIT
The monitor switch is mechanically controlled by oven door, and
monitors the operation of the secondary interlock switch, the relay
(RY1) and the primary interlock relay.
monitors the operation of the secondary interlock switch, the relay
(RY1) and the primary interlock relay.
1) When the oven door is opened during or after the cycle of a
cooking program, the secondary interlock switch and door sens-
ing switch must open their contacts first. After that the contacts
(COM-NC) of the monitor switch can be closed.
ing switch must open their contacts first. After that the contacts
(COM-NC) of the monitor switch can be closed.
2) When the oven door is closed, the contacts (COM-NC) of the
monitor switch must be opened. After that the contacts of the
secondary interlock switch and door sensing switch are closed.
secondary interlock switch and door sensing switch are closed.
3) When the oven door is opened and the contacts of the second-
ary interlock switch and the primary interlock relay (RY2) remain
closed. The fuse T6.3A will blow, because the monitor switch is
closed and a short circuit is caused.
closed. The fuse T6.3A will blow, because the monitor switch is
closed and a short circuit is caused.
2. MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
COOKING
When the microwave oven is preset for variable cooking power, rated
voltage is supplied to the high voltage transformer intermittently within
a 32-second time base through the relay contact which is coupled with
the current-limiting relay RY2. The following levels of microwave
power are given.
voltage is supplied to the high voltage transformer intermittently within
a 32-second time base through the relay contact which is coupled with
the current-limiting relay RY2. The following levels of microwave
power are given.
SETTING;
NOTE: The ON/OFF time ratio does not exactly correspond to the
percentage of microwave power, because approx. 3 seconds
are needed for heating up the magnetron filament.
are needed for heating up the magnetron filament.
[3] POWER OUTPUT REDUCTION
After 100% power cooking mode is carried out for more than 20 min-
utes, the power out-put is automatically reduced to 70%. Even if the
cooking time is shorter than for 20 minutes, the power output is
reduced to 70% after total cooking time over 20 minutes when the
oven is started in 100% power cooking mode again within 1 minute
and 35 seconds.
utes, the power out-put is automatically reduced to 70%. Even if the
cooking time is shorter than for 20 minutes, the power output is
reduced to 70% after total cooking time over 20 minutes when the
oven is started in 100% power cooking mode again within 1 minute
and 35 seconds.
CONNECTED COMPONENTS
RELAY
Oven lamp, Fan motor, Turntable motor
RY5
high voltage transformer
RY2
CONDITION
SWITCH CONTACT
DURING
COOKING
DOOR OPEN
(NO COOKING)
Secondary interlock
switch
switch
COM-NO Closed
Open
COM-NC
Open
Closed
Door sensing switch
COM-NO
Closed
Open
Monitor switch
COM-NC
Open
Closed
100P (HIGH)
32 sec. ON
70P (MEDIUM
HIGH)
Approx. 70%
100%
24 sec. ON
8 sec. OFF
14 sec. OFF
20 sec. OFF
26 sec. OFF
50P (MEDIUM)
Approx. 50%
18 sec. ON
30P (MEDIUM
LOW)
Approx. 30%
12 sec. ON
10P (LOW)
Approx. 10%
6 sec. ON
Display
