DOWNLOAD Sharp R-28STM Service Manual ↓ Size: 4.21 MB | Pages: 23 in PDF or view online for FREE

Model
R-28STM
Pages
23
Size
4.21 MB
Type
PDF
Document
Service Manual
Brand
Device
Home Appliance / Microwave Oven
File
r-28stm.pdf
Date

Sharp R-28STM Service Manual ▷ View online

 
 
 
INSTALLATIONS 
 
INSTALLING 
1. Empty the microwave oven and clean inside it with 
a soft, damp cloth. Check for damage such as 
misaligned door, damage around the door or dents 
inside the cavity or on the exterior. 
 
2. Put the oven on a counter, table, or shelf that is 
strong enough to hold the oven and the food and 
utensils you put in it. (The control panel side of the 
oven is the heavy side. Use care when handling.) 
 
3. Do not block the vent and the air intake openings. 
Blocking vent or air intake openings can cause 
damage to the oven and poor cooking results. 
Make sure the microwave oven legs are in place to 
ensure proper air flow. 
 
4. The oven should not be installed in any area where 
heat and steam are generated, because they may 
damage the electronic or mechanical parts of the 
unit. 
Do not install the oven next to a conventional 
surface unit or above a conventional wall oven. 
 
5. Use microwave oven in an ambient temperature 
less than 104°F(40°C). 
 
6. Place the microwave oven on a sturdy and flat 
surface at least 10 cm(4 inches) from the wall. 
 
7. Place the microwave oven as far away as possible 
from TV, RADIO, COMPUTER, etc., to prevent 
interference. 
 
 
BEFORE YOU BEGIN, READ THE FOLLOWING INSTRUCTIONS COMPLETELY 
EARTHING INSTRUCTIONS 
This microwave oven is designed to be used in a fully 
earthed condition. 
It is imperative, therefore, to make sure it is properly 
earthed before servicing 
WARNING-   
THIS  APPLIANCE 
MUST BE EARTHED 
IMPORTANT
 
 
The wires in this mains lead are colored in 
accordance with the following code: 
Green-and-yellow:              Earth 
Blue:                                      Neutral 
Brown:                                  Live
 
As the colors of the wires in the mains lead of this 
appliance may not correspond with the colored 
markings identifying the terminals in your plug, 
proceed as follows. 
 
The wire which is colored 
green-and-yellow must be 
connected to the terminal in the plug which is marked 
with the letter 
or by the earth symbol (
 ) or 
colored 
green or green-and-yellow
 
The wire which is colored 
blue must be connected to 
the terminal in the plug which is marked with the letter 
or colored black
 
The wire which is colored 
brown must be connected 
to the terminal in the plug which is marked with the 
letter 
or colored red
3-1 
SCHEMATIC DIAGRAM
TCO.
 
 
4-2 
 
 
CIRCUIT DESCRIPTION
 
 
 
 
 
 
 
GENERAL DETAILS
• The low voltage transformer supplies the necessary
voltage to the micom controller when power cord is
plugged in.
• When the door is closed, the primary switch is ON, the
secondary switch is ON, and the monitor switch opens
(contact COM and NO).
WHEN SELECTING COOKING POWER
LEVEL AND TIME
• The micom controller memorizes the function you set.
• The time you set appears in the display window.
• Each indicator light turns on to indicate that the stage
has been set.
WHEN TOUCHING THE START PAD
• The coil of the relay is energized by the micom
controller.
• Power input is supplied to the high voltage transformer
through the fuse to the primary switch and relay 2.
• Turntable rotates.
• The fan motor rotates and cools the magnetron by
blowing the air (coming from the intake on the
baseplate)
• The air is also directed into the oven to exhaust the
vapor in the oven through the upper plate.
• Cooking time starts counting down.
• 3.2 volts AC is generated from the filament winding of
the high voltage transformer. This 3.2 volts is applied
to the magnetron to heat the magnetron filament
through two noise preventing choke coils.
• A high voltage of approximately 2100 volts AC is
generated in the secondary of the high voltage
transformer which is increased by the action of the high
voltage diode and charging of the high voltage
capacitor.
• The negative 4,000 Volts DC is applied to the filament
of the magnetron.
WHEN THE OVEN IS SET AT ANY LEVEL
EXCEPT MAXIMUM.
• The micom controller controls the ON-OFF time of relay
2 by the applied signal to vary the average output 
power of microwave oven as POWER LEVEL.
WHEN THE DOOR IS OPENED DURING
COOKING
• Both the primary switch and relay 2 are cut off primary
winding voltage of the high voltage transformer.
• ON-OFF of relay 2 is coupled electrically with opening
and closing of the secondary switch.
• When the door is opened, the secondary switch is
opened and when the door is closed, the secondary
switch is closed.
• The cooking time stops counting down.
• Relay stops functioning.
• As the door is opened, if the contact of primary switch
and relay 2 and/or secondary switch fails to open, the
fuse opens due to the large current surge caused by
the monitor switch activation, which in turn stops
magnetron oscillation.
L
FUSE
TRANS-
FORMER
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
SWITCH
N
MONITOR
SWITCH
PRIMARY
MONITOR
SWITCH
L
FUSE
RELAY 2
MICOM CONTROLLER
SECONDARY
SWITCH
PRIMARY
SWITCH
N
TRANS-
FORMER
 
 
 
SERVICE INFORMATION 
TOOLS AND MEASURING INSTRUMENTS
 
NECESSARY TOOLS 
Tools normally used for TV servicing are sufficient. 
Standard tools are listed below. 
• Diagonal pliers 
• Long nose pliers 
• Phillips screwdriver 
• Flat blade screwdriver 
• Wrench (size 5mm) 
• Nutdriver (size 5mm) 
• Adjustable wrench 
• Soldering iron 
• Solder 
• Vinyl insulation tape 
• Polishing cloth 
 
 
MICROWAVE LEAKAGE TEST
 
CAUTIONS 
• Be sure to check microwave leakage prior to 
servicing the oven if the oven is operative prior to 
servicing. 
• The service personnel should inform the 
manufacture importer, or assembler of any certified 
oven unit found to have a microwave emission 
level in excess of 5 mW/cm
2
 
and should repair any 
unit found to have excessive emission levels at no cost 
to the owner and should ascertain the cause of the 
excessive leakage. The service personnel should 
instruct the owner not to use the unit until the oven has 
been brought into compliance. 
• If the oven operates with the door open, the service 
personnel should: 
- Tell the user not to operate the oven. 
- Contact the manufacturer. 
• The service personnel should check all surface and 
vent openings for microwave leakage. 
• Check for microwave leakage after every servicing. The 
power density of the microwave radiation leakage 
emitted by the microwave oven should not exceed 
5 mW/cm
2
. Always start measuring of an unknown field 
to assure safety for operating personnel from radiation 
leakage. 
 
NECESSARY MEASURING 
INSTRUMENTS 
• TESTER(VOLTS-DC, AC., Ohmmeter) 
• Microwave survey meter 
- Holaday HI-1710(A) 
- Narda 8100 
8200 
• Inch scale 
• 600 cc non conductive material beaker (glass or 
plastic), inside diameter: approx. 8.5 cm(3
1/2 
in.) 
• Cylindrical and made of borosilicate glass vessel. 
max. thickness: 3 mm 
outside diameter: approx. 190mm 
height: approx. 90mm 
• Glass thermometer: 100°C or 212°F (1 deg scale) 
MEASURING MICROWAVE ENERGY 
LEAKAGE 
• Pour 275±15 cc of 20±5°C(68±9°F) water in a 
beaker 
which is graduated to 600 cc, and place the beaker 
on the center of the turntable. 
• Set the energy leakage monitor to 2,450 MHz and 
use it following the manufacturer's recommended 
test procedure to assure correct result. 
• When measuring the leakage, always use the 2-
inch (5 cm) spacer supplied with the probe. 
• Operate the oven at its maximum output. 
• Measure the microwave radiation using and 
electromagnetic radiation monitor by holding the 
probe perpendicular to the surface being measured 
Move probe along shaded area 
Probe scanning speed: Less than 2.5 cm/sec 
 
5-1 
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