http://www.LGEservice.com
E-mail:Techsupport@LGEservice.com
MICROWAVE OVEN
SERVICE MANUAL
MODEL : MA-1103W/MA-1103B
CAUTION
BEFORE SERVICING THE UNIT, READ THE
SAFETY PRECAUTIONS IN THIS MANUAL.
SAFETY PRECAUTIONS
This device is to be serviced only by properly qualified service personnel.
Consult the service manual for proper service procedures to assure continued safety operation and for precautions to be taken to avoid possible exposure to excessive microwave energy.
PRECAUTIONS TO BE OBSERVED BEFORE AND DURING SERVICING TO AVOID POSSIBLE EXPOSURE TO EXCESSIVE MICROWAVE ENERGY
A)Do not operate or allow the oven to be operated with the door open.
B)Make the following safety checks on all ovens to be serviced before activating the magnetron or other microwave source, and make repairs as necessary; (1) interlock operation, (2) proper door closing, (3) seal and sealing surfaces (arcing, wear, and other damage), (4) damage to or loosening of hinges and latches, (5) evidence of dropping or abuse.
C)Before turning on microwave power for any service test or inspection within the microwave generating compartments, check the magnetron, wave guide or transmission line, and cavity for proper alignment, integrity, and connections.
D)Any defective or misadjusted components in the interlock, monitor, door seal, and microwave generation and transmission systems shall be repaired, replaced, or adjusted by procedures described in this manual before the oven is released to the owner.
E)A microwave leakage check to verify compliance with the Federal Performance Standard should be performed on each oven prior to release to the owner.
CONTENTS
(Page)
SAFETY PRECAUTIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - Inside front cover SPECIFICATIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 1-1 CAUTIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 2-1 INSTALLATIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3-1 OPERATING INSTRUCTIONS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4-1
FEATURES- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4-1 CONTROL PANEL - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4-1 OPERATING SEQUENCE- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4-2 SCHEMATIC DIAGRAM - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4-3 CIRCUIT DESCRIPTION - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 4-4
SERVICE INFORMATION - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5-1
TOOLS AND MEASURING INSTRUMENTS - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5-1 MICROWAVE LEAKAGE TEST - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5-1 MEASUREMENT OF MICROWAVE POWER OUTPUT - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5-3 DISASSEMBLY AND ADJUSTMENT - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5-3 INTERLOCK CONTINUITY TEST- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5-7 COMPONENT TEST PROCEDURE - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5-8 TROUBLE SHOOTING - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 5-11
EXPLODED VIEW - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 6-1 REPLACEMENT PARTS LIST - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 7-1 SCHEMATIC DIAGRAM OF P.C.B. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 8-1
PRINTED CIRCUIT BOARD - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 8-2
P.C.B. PARTS LIST - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 9-1
SPECIFICATIONS
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DESCRIPTION |
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MODEL |
MA-1103W/MA-1103B |
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Power Requirement |
120 Volts AC 60 Hz |
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1,550 Watts |
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Single phase, 3 wire grounded |
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Power Output |
1,150 Watts full microwave power (IEC705) |
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Microwave Frequency |
2,450 MHz |
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Magnetron |
2M246, 2M248J |
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Timer |
0 ~ 99 min. 99 sec. |
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Outside Dimensions |
207/8 (W) x 123/8 (H) x 151/2 (D) |
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Cavity Dimensions |
133/4 (W) x93/8 (H) x 143/8 (D) |
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Net Weight |
35 lbs (approx.) |
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Shipping weight |
38 lbs (approx.) |
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Control Complement |
Touch Control System |
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Clock : 1:00 - 12:59 |
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Microwave Power for Variable Cooking |
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Power level |
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HIGH ---------------------------------------- |
Full power throughout the cooking time |
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9 (Saute) ------------------------- |
approx. 90% of Full power, |
8 (Reheat) -------- |
approx. 80% |
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7 (Med.-High) -------------------- |
approx. 70%, |
6 (Medium) -------- |
approx. 60% |
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5 (Med.-Low) -------------------- |
approx. 50%, |
4 (Defrost) --------- |
approx. 40% |
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3 (Low) --------------------------- |
approx. 30%, |
2 (Simmer)--------- |
approx. 20% |
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1 (Warm)-------------------------- |
approx. 10% |
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Nameplate Location |
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Back Side
Accessories |
Owner's manual & cooking guide |
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Glass turntable |
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Rotating ring |
This microwave oven is designed for household use only.
It is not recommended for commercial purposes.
1-1
CAUTIONS
Unlike other appliances, the microwave oven is high-voltage and high-current equipment. Though it is free from danger in ordinary use, extreme care should be taken during repair.
•DO NOT operate on a 2-wire extension cord during repair and use.
•NEVER TOUCH any oven components or wiring during operation.
•BEFORE TOUCHING any parts of the oven, always remove the power plug from the outlet.
•For about 30 seconds after the oven stops, an electric charge remains in the high voltage capacitor. When replacing or checking, you must discharge the high voltage capacitor by shorting across the two terminals with an insulated screwdriver.
•Remove your watches whenever working close to or replacing the Magnetron.
•DO NOT touch any parts of the control panel circuit. A resulting static electric discharge may damage this P.C.B.
•NEVER operate the oven with no load.
•NEVER injure the door seal and front plate of the oven cavity.
•NEVER put iron tools on the magnetron.
•NEVER put anything into the latch hole and the interlock switches area.
MICROWAVE RADIATION
Personnel should not be exposed to the microwave energy which may radiate from the magnetron or other microwave generating device if it is improperly used or connection. All input and output microwave connections, waveguide, flange, and gasket must be secure never operate the device without a microwave energy absorbing load attached.
Never look into an open waveguide or antenna while the device is energized.
•Proper operation of the microwave oven requires that the magnetron be assembled to the waveguide and cavity. Never operate the magnetron unless it is properly installed.
•Be sure that the magnetron gasket is properly installed around the dome of the tube whenever installing the magnetron.
ANTENNA
Gasket
COOLING FIN
FILAMENT
TERMINALS
MAGNETRON
CHASSIS GROUND
MAGNETRON
THE OVEN IS TO BE SERVICED ONLY BY PROPERLY QUALIFIED SERVICE PERSONNEL.
2-1
INSTALLATIONS
BEFORE YOU BEGIN, READ THE FOLLOWING INSTRUCTIONS COMPLETELY AND CAREFULLY.
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.
GROUNDING INSTRUCTIONS
For personal safety, this appliance must be fully grounded at all times.
In the event of an electrical short circuit, grounding reduces the risk of electrical shock.
The plug must be plugged into an outlet that is properly installed and grounded.
WARNING
Improper use of the grounding plug can result in a risk of electric shock.
Do not, under any circumstances, cut or remove the third ground prong from the power cord plug.
PREFERRED METHOD
ENSURE PROPER GROUND
EXISTS BEFORE USE
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.
10cm
TEMPORARY METHOD (ADAPTER PLUGS NOT PERMITTED IN CANADA)
ALIGN LARGE
PRONGS/SLOTS
ENSURE PROPER GROUND
AND FIRM CONNECTION
BEFORE USE
3-1
OPERATING INSTRUCTIONS
FEATURES
Oven Front Plate
Window Door Screen
Door Seal
Display Window
Control Panel
Safety Door Lock System
Turntable
Rotating Ring
CONTROL PANEL
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1. DISPLAY WINDOW. |
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1150W |
2. ONE TOUCH CONTROL: This menu has been pre |
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programmed to cook food automatically by one touch. |
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3. |
AUTO DEFROST: This feature provides you with the best |
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defrosting method for frozen foods. |
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4. |
CUSTOM COOK: This feature allows you to set and execute |
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a frequently used single stage program. |
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5. |
NUMBER: These used to set for time of day, cooking time, |
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power level, or defrost weight. |
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6. |
MORE / LESS: All of the one touch cook and TIMED COOK |
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can be adjusted to cook food for a longer or shorter time. |
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MORE |
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Pressing MORE will add 10 seconds to the |
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cooking time. |
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3 |
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8 |
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LESS |
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Pressing LESS will subtract 10 seconds of |
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cooking time. |
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7. |
STOP/CLEAR: It used to stop oven and clear all entries |
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9 |
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except time of day. |
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8. |
CUSTOM SET: You can select sound on/off, auto start |
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on/off, lbs/kg choice mode. |
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10 |
9. |
TIME: You can set the desired cook time. |
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10. POWER: You can select the desired power level for |
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cooking. |
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11 |
11. CLOCK: It is used to set the time of day. |
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6 |
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12. EZ ON. |
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13. START: This feature allows oven to begin functioning. |
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4-1
OPERATING SEQUENCE
The following is a description of component functions during oven operation.
1. SETTING THE CLOCK
STOP/CLEAR 
CLOCK 
NUMBER 
CLOCK
ex.) To set 4:30, touch number key [4],[3], and [0]. NOTE: 1) This is a 12 hour clock.
2)Clock will operate as long as power is applied to the oven.
2.CANCEL FUNCTION
Touch the STOP/CLEAR pad whenever you need to cancel an entry or a function currently in use.
The display will either return to the last item entered or to the clock.
3. EZ ON
STOP/CLEAR |
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4. ONE TOUCH COOKING
STOP/CLEAR |
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POPCORN |
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NOTE: Heat only 1 package at a time.
5. TIME COOKING
STOP/CLEAR 
TIME 
NUMBER 
POWER
NUMBER 
START
6. MULTI-STAGE COOKING
1ST STAGE
STOP/CLEAR 
TIME 
NUMBER 
POWER
NUMBER
2ND STAGE
TIME 
NUMBER 
POWER
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7. AUTO DEFROST COOKING
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AUTO |
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DEFROST |
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WEIGHT |
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8. CHILD LOCK
This oven has a CHILD LOCK feature
TO SET CHILD LOCK |
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• Touch and hold |
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the display. |
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TO CANCEL CHILD LOCK |
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• Touch and hold |
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9. MORE / LESS
The cook time is adjustable by MORE pad or LESS pad
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COOKING |
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COOKING |
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10. CUSTOM COOK
You can program the cook time and power level by using CUSTOM COOK pad.
STOP/CLEAR |
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COOK |
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NUMBER 
START
11. CUSTOM SET
You can select ON/OFF of beeper, automatic start or manual start of the one touch cook, and food weight measurement unit, pounds or kilograms.
• ON/OFF of beeper
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•To select automatic start or manual start of one touch cook.
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CUSTOM |
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• To select weight unit (LBS/kg) |
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4-2
3-4
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FUSE |
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PRIMARY |
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H.V. |
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SCHEMATIC |
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20A |
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BK |
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TRANSFORMER |
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RD |
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BK |
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MICOM |
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BN |
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DIAGRAM |
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CONTROLLER |
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1 |
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RD |
BK |
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PT1 |
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RD |
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TURN |
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MONITOR |
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3 |
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OVEN |
TABLE |
SWITCH |
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RY1 |
MOTOR |
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LAMP |
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4 |
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F.M. |
FAN |
T.T.M. |
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CAPACITOR |
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MOTOR |
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GN |
BL |
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H.V. DIODE |
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6 |
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N |
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7 |
GN |
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AC |
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WH |
WH |
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8 |
PK |
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CN1 |
RY2 |
SECONDARY |
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MAGNETRON |
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SWITCH |
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YL |
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WH |
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** NOTE : DOOR IS OPENED. |
BK : BLACK |
BL : BLUE YL : YELLOW |
RD : RED |
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WH : WHITE |
PK : PINK GN : GREEN |
BN : BROWN |
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IMPORTANT SAFETY NOTE: THE SHADED AREAS ON THIS SCHEMATIC DIAGRAM INCORPORATE SPECIAL FEATURES IMPORTANT FOR PROTECTION FROM MICROWAVE RADIATION, FIRE, ELECTRICAL SHOCK, AND HAZARDS. WHEN SERVICING IT IS ESSENTIAL THAT ONLY MANUFACTURER'S SPECIFIED PARTS BE USED FOR THE CRITICAL COMPONENTS IN THE SHADED AREAS OF THE SCHEMATIC DIAGRAM.
NOTICE: SINCE THIS IS BASIC SCHEMATIC DIAGRAM, THE VALUES OF COMPONENTS AND
SOME PARTIAL CONNECTIONS ARE SUBJECT TO CHANGE FOR IMPROVEMENT.
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.
PRIMARY
FUSE SWITCH
L |
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MONITOR |
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N |
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RELAY 2 |
SECONDARY |
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MICOM CONTROLLER
•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.
•3.3 volts AC is generated from the filament winding of the high voltage transformer. This 3.3 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.
(refer to page 1-1)
•One complete cycle of relay 2 is 22 seconds.
WHEN THE DOOR IS OPENED DURING COOKING
•Both the primary switch and relay 2 cut off the 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 relay2 and/or secondary switch fail to open, the fuse opens due to the large current surge caused by the monitor switch activation, which in turn stops magnetron oscillation.
PRIMARY
FUSE SWITCH
L
MONITOR |
H.V. |
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SECONDARY
RELAY 2 |
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MICOM CONTROLLER |
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4-4
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
NECESSARY MEASURING INSTRUMENTS
•TESTER (VOLTS-DC, AC, Ohmmeter)
•Microwave survey meter
-Holaday HI-1500
HI-1501 - Narda 8100
8200
•Inch scale
•600 cc non conductive material beaker (glass or plastic),
inside diameter: approx. 8.5 cm (31/2 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)
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 manufacturer, importer, or assembler of any certified oven unit found to have a microwave emission level in excess of 5 mW/cm2 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 and CDRH
(Center for Devices and Radiological Health) immediately.
NOTE: Address on CDRH
Office of Compliance(HFZ-312) Center for Devices and Radiological Healthe 1390, Piccard Drive, Rockville. MD 20850
•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
4 mW/cm2. Always start measuring of an unknown field to assure safety for operating personnel from radiation leakage.
MEASURING MICROWAVE ENERGY LEAKAGE
•Pour 275±15cc 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 (5cm) 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 ( 1in/sec)
5-1
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