R-752M (serv.man2) — Sharp Home Appliance Service Manual (repair manual)

Model
R-752M (serv.man2)
Pages
23
Size
328.08 KB
Type
PDF
Document
Service Manual
Brand
Device
Home Appliance / Microwave Oven
File
r-752m-sm2.pdf
Date

View Sharp R-752M (serv.man2) Service Manual online

1
752M -
WARNING TO SERVICE PERSONNEL
Microwave ovens contain circuitry capable of producing very high voltage and current.  Contact with the following parts
will result in electrocution.
High voltage capacitor, High voltage transformer, Magnetron, High voltage rectifier assembly, High voltage harness.
REMEMBER TO CHECK 4R
1) Reconnect all leads removed from components
during testing.
2) Replace the outer case (cabinet).
3) Reconnect the supply.
4) Run  the oven. Check all functions.
Microwave ovens should not be run empty. To test for
the presence of microwave energy within a cavity, place
a cup of cold water on the oven turntable, close the door
and set the power to HIGH and set the microwave timer
for two (2) minutes. When the two minutes has elapsed
(timer at zero) carefully check that the water is now hot.
If the water remains cold carry out 3D checks and re-
examine the connections to the component being tested.
REMEMBER TO CHECK 3D
1) Disconnect the supply.
2) Door opened, and wedged open.
3) Discharge high voltage capacitor.
WARNING AGAINST THE CHARGE OF THE
HIGH-VOLTAGE CAPACITOR
The high-voltage capacitor remains charged about
60 seconds after the oven has been switched off.
Wait for 60 seconds and then short-circuit the
connection of the high-voltage capacitor (that is,
of the connecting lead of the high-voltage recti-
fier) against the chassis with the use of an insu-
lated screwdriver.
Sharp recommend that wherever possible fault-finding
is carried out with the supply disconnected. It may in,
some cases, be necessary to connect the supply after
the outer case has been removed, in this event carry out
3D checks and then disconnect the leads to the primary
of the power transformer. Ensure that these leads
remain isolated from other components and the oven
chassis. (Use insulation tape if necessary.) When the
testing is completed carry out 3D checks and reconnect
the leads to the primary of the power transformer.
When all service work is completed, and the oven is fully assembled, the microwave power output should be checked
and a microwave leakage test carried out.
WARNING
Servicing and repair work must be carried out only by
trained service engineers.
All the parts marked "*" on parts list are used at
voltages more than 250V.
Removal of the outer wrap gives access to potentials
above 250V.
All the parts marked "
" on parts list may cause undue
microwave exposure, by themselves, or when they
are damaged, loosened or removed.
CAUTION
MICROWAVE RADIATION
Service engineers should not be exposed to the
microwave energy which may radiate from the
magnetron or other microwave generating de-
vices if it is improperly used or connected. All
input and output microwave connections,
waveguides, flanges and gaskets must be se-
cured. Never operate the device without a micro-
wave energy absorbing load attached. Never
look into an open waveguide or antenna while the
device is energized.
Whilst the maximum leakage permitted in BS EN 60335-2-25 is 50Wm2 (equivalent to 5mW/cm2, it is not normal to
detect any significant leakage, and therefore any detected leakage should be investigated.
WARNING
THIS APPLIANCE MUST BE EARTHED
THE WIRES IN THIS MAINS LEAD ARE COLOURED IN
ACCORDANCE WITH THE FOLLOWING CODE:
GREEN-AND-YELLOW : EARTH        BLUE : NEUTRAL        BROWN : LIVE
CAUTION/WARNING
SERVICING
2
752M -
PRODUCT SPECIFICATIONS
ITEM
DESCRIPTION
Power Requirements
230-240 Volts           50 Hertz         Single phase, 3 wire grounded
Power Consumption
Microwave cooking   1.55 kW Approx.     7 A
Grill cooking              1.25 kW Approx.   5 A
Dual cooking             2.75 kW Approx. 12 A
Power Output
900W watts nominal of RF microwave energy
(measured by way of IEC 705) Operating frequency of 2450 MHz
Grill Heating Element Power Output
1200W (600W x 2)
Case Dimensions
Width 520mm     Height 305mm including foot     Depth 413mm
Cooking Cavity Dimensions
Width 342mm     Height 207mm                           Depth 368mm
Turntable diameter
325mm
Control Complement
Touch Control System     Clock(1:00-12:59 or 0:00-23:59)
Timer (0-99 minutes 90 seconds)
Microwave Power for Variable Cooking Repetition Rate;
HIGH Full power throughout the cooking time
MEDIUM HIGH approx. 70% of Full Power
MEDIUM approx. 50% of Full Power
MEDIUM LOW approx. 30% of Full Power
LOW ...  approx. 10% of Full Power
FUNCTION KEYS:
AUTO COOK keys
INSTANT COOK keys
AUTO DEFROST key LESS (    )/MORE (    ) keys,
Time keys
MICROWAVE POWER LEVEL key,
GRILL key
DUAL GRILL key, STOP/CLEAR key,
TIMER key
AUTO MINUTE/START key
AUTO START CLOCK key
WEIGHT keys
Set Weight
Approx. 18 kg
3
752M -
IMPORTANT
When the oven door is closed, the monitor switch contacts
COM - NC must be open.
MICROWAVE COOKING CONDITION
HIGH COOKING
When the door is opened during a cook cycle, the switches
come to the following condition.
CONDITION
DURING
DOOR OPEN
SWITCH
CONTACT
COOKING
(NO COOKING)
Monitored latch switch
COM-NO
Closed
Open
Monitor switch
COM-NC
Open
Closed
COM-NO
Closed
Open
Stop switch
COM-NO
Closed
Open
When the oven door is opened and the contacts of the
monitored latch switch SW1 remain closed, the fuse F8A
will blow.
MEDIUM HIGH, MEDIUM, MEDIUM LOW, LOW
COOKING
The following levels of microwave power are given.
SETTING
DUAL COOKING CONDITION
1.  The contact of monitored latch switch SW1 are
closed.
2.  The relay RY1, RY2 and RY3 are energised.
3.  When cooking in dual mode the microwave power is
limited to 70% (via the I.C.).
Approx. 100%
Approx. 50%
Approx. 30%
30 sec. ON
HIGH
LOW
24 sec. ON
6 sec. OFF
18 sec. ON
10 sec. ON
5 sec. ON
12 sec. OFF
20 sec. OFF
25 sec. OFF
MEDIUM
MEDIUM HIGH
MEDIUM LOW
Approx. 70%
Approx. 10%
FUNCTION OF IMPORTANT COMPONENTS
DOOR OPEN MECHANISM
Figure D-1.  Door Open Mechanism
MONITOR
SWITCH
MONITORED
LATCH  SW
OPEN LEVER
DOOR
STOP SWITCH
DOOR OPEN BUTTON
LATCH HOOK
LATCH
HEAD
MONITORED LATCH SWITCH SW1
STOP SWITCH SW3
1.  When the oven door is closed, the contacts (COM-
NO) must be closed.
2.  When the oven door is opened, the contacts (COM-
NO) must be opened.
MONITOR SWITCH SW2
I
f the oven door is opened and the contacts
(COM-NO) of the monitored latch switch SW1 fail
to open, the fuse F8A blows simultaneously with
closing the contacts (COM-NC) of the monitor
switch SW2.
CAUTION:  BEFORE REPLACING A BLOWN
FUSE F8A TEST THE MONITORED
LATCH SWITCH SW1, MONITOR
SWITCH SW2.
OPERATING SEQUENCE
4
752M -
A
MICROWAVE OUTPUT POWER
The power output of this oven is rated using the method specified by IEC-705.  Full
details of how to carry out this
procedure can be found in the Sharp Technical Training notes which is available from
Sharp Parts Centre
(part number SERV-LITMW01).
The IEC-705 procedure must be carried out using laboratory-type procedures
and equipment.
These requirements make the procedure unsuitable for routine performance checks.
Note: The following test method gives an indication of the output power only, it cannot
be used to establish the actual/rated output power.  If the true output power is
required, then the IEC-705 test method must be used.
Alternative simplified method:
1.
Place 2 litres of cold water (between 12
°
C and 20
°
C) in a suitable container.
2.
Stir the water and measure the temperature in 
°
C.  Note temperature as T1.
3.
Place the container in the microwave and heat the water for 2 minutes on full power.
4.
When the 2 minutes is completed, remove the container and stir the water.  Note the
water temperature as T2.
5.
Calculate the output power using the following formula:
R.F. Power Output = (T2 - T1) x 70.
Note:  The result from this test should be within the allowance of 2000cc alternative
method. (+-10%).
MICROWAVE LEAKAGE TEST
This oven should be tested for microwave leakage on completion of any repair or
adjustment, following the procedure described in the Sharp Technical Training notes
(part number SERV-LITMW01).  The maximum leakage permitted in BS EN 60335-2-
25 is 50W/m
(equivalent to 5mW/cm
2
), however it is not normal to detect any signifi
cant leakage, therefore, any leakage which is detected should be investigated.
It is essential that only leakage detectors with current calibration traceable to the National
Physical  Laboratories are used.
Suitable leakage detectors :
CELTEC A100
APOLLO X1
  
TEST PROCEDURES
PROCEDURE
LETTER
COMPONENT TEST
Page of 23
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