Read Sharp R-757M (serv.man6) Service Manual online
(monitored latch switch and stop switch).
When the oven door is closed, the monitor switch
contacts COM-NC must be open. When the micro-
wave oven is plugged in a wall outlet (230-240V /
50Hz), the line voltage is supplied to the point A1+A3
in the control unit.
2. To set the any programmes or set the clock, you must
Enter a desired cooking time by pressing TIME keys. And
choose the 100P microwave power by pressing MICRO-
WAVE POWER LEVEL key. And then start the oven by
pressing the START key.
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.
sent to the voltage doubling circuit, where it is doubled
to negative voltage of approximately 4000 volts D.C..
energy is channelled through the waveguide (transport
channel) into the oven cavity, where the food is placed
to be cooked.
The circuits to the oven lamp, high voltage transformer,
fan motor and turntable motor are cut off.
and turntable motor are cut off when the monitored
latch switch and stop switch are made open. The oven
lamp remains on even if the oven door is opened after
the cooking cycle has been interrupted, because the
oven door, and monitors the operation of the moni-
tored latch switch.
switch and stop switch must open their contacts first.
After, the contacts (COM-NC) of the monitor switch
the contacts of the monitored latch switch and the
stop switch are closed.
F8A will blow, because the monitor switch is closed
and a short circuit is made.
power, the line voltage is supplied to the high voltage
transformer intermittently within a 32-second time base
through the relay contact which is coupled with the cur-
rent-limiting relay RY3. The following levels of microwave
power are given.
to the percentage of microwave power, because
approx. 3 seconds are needed for heating up the
energy. Programme the desired cooking time by pressing
TIME keys, and choose the grill mode by pressing GRILL
key once. When the START key is pressed, the following
5. Upon completion of the selected cooking time, audible
the activated components as items 3 are de-energized.
the door handle is pulled, the latch head is moved upward,
and released from the latch hook, now the door can be
10%-70%) + Grill
1. If the multiple sequence cooking is carried out in the
calculated from the first.
from the first.
the microwave or the grill will be reduced to 70% after
20 minutes when the oven is started at first.
energy and grill heating element energy simultaneously.
Enter the desired cooking time by pressing TIME keys.
And choose the dual grill mode by pressing DUAL GRILL
key. And choose the microwave power level by pressing
DUAL GRILL or MICROWAVE POWER LEVEL key. When
the START key is pressed, the following operations occur:
the activated cpmponents as items 3 are de-energized.
ONE/AUTO CLOCK PROGRAMME
computed and selected based on the programmes.
second time base. The following table is the ON / OFF time
ratio at each power output of the magnetron.
the basis cooking time, the power output is automatically
reduced by turning the control relays on and off intermit-
tently, as shown in the table below. This is to protect the
oven door against temperature rising.
blows simultaneously with closing the contacts (COM-
NC) of the monitor switch.
AND MONITOR SWITCH FOR PROPER
OPERATION. (REFER TO CHAPTER “TEST
circuited, this fuse blows to prevent an electric shock of
closed with the oven door open and when the contact
(COM-NC) of monitor switch closes.
1. If the wire harness or electrical components are short-
or fire hazard.
magnetron or secondary winding of high voltage trans-
former is shorted.
heat. If the temperature goes up higher than 125˚C be-
cause the fan motor is interrupted or the ventilation open-
ings 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 defec-
tive thermal cut-out must be replaced with a new one.
is designed to prevent damaged to the oven if the food in
the oven catch fire due to over heating produced by
improper sitting of cooking time or failure of control unit.
Under normal operation, the oven thermal cut-out remains
closed. However, when abnormally high temperature is
reached within the oven cavity, the oven thermal cut-out
will open at 145˚C, causing the oven to shut down. When
the thermal cut-out cools itself down to the operating
temperature of 115˚C, the contacts of the thermal cut-out
will close again.
This cool air is directed through the air vanes surrounding
the magnetron and cools the magnetron. This air is chan-
nelled 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.
is located on the top of the oven cavity.
might flow back in to the power circuit.
current flow in both directions. And it prevents the tem-
perature rise of the high voltage transformer by blowing
the fuse F8A when the high voltage rectifier is shorted.
rectifier is 6 KV The rated peak reverse voltage of D2 of the
asymmetric rectifier is 1.7 KV. D1 and D2 of the asymmet-
ric 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
1. The high voltage rectifier is shorted by some fault when
voltage doubler circuit.
4. The large electric currents flow through the high volt-
7. The power supplying to the high voltage transformer is