Daewoo Microwave Oven Service Manual

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 connection.

(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.

Specifications

* Specifications subject to change without notice.

Diagram: Shows a front and side view of the microwave oven with dimensions. The front view shows controls and the door. The side view shows depth (D) with specific measurements for KOG-36250s (352mm) and KOG-36450s (354mm). The overall width is 465mm and height is 274mm.

Features Diagram

The diagram illustrates the various components of the microwave oven, labeled with numbers:

• 1. Saftey Interlock System
• 2. Door Viewing Screen
• 3. Door Hook
• 4. Oven Cavity
• 5. Door Seal
• 6. Glass Cooking Tray
• 7. Roller Guide
• 8. Coupler
• 9. Knob V.P.C.
• 10. Knob Timer
• 11. Door Release Button
• 12. Reflector (Insulator Heater)
• 13. Heating Element
• 14. Metal Rack

Descriptions of Features:

• Saftey Interlock System: Ensures the oven does not operate when the door is open.
• Door Viewing Screen: Allows viewing of food while preventing microwave leakage.
• Door Hook: Secures the door and stops the magnetron when the door is opened during operation.
• Oven Cavity: The interior space where food is placed.
• Door Seal: Maintains microwave energy within the cavity and prevents leakage.
• Glass Cooking Tray: Heat-resistant glass tray for cooking food.
• Roller Guide: Supports the glass cooking tray.
• Coupler: Fits over the shaft in the cavity floor to rotate the tray.
• Knob V.P.C.: Variable Power Controller for selecting microwave power level.
• Knob Timer: Used for setting cooking time.
• Door Release Button: Disengages the latch system to open the door.
• Reflector (Insulator Heater): Reflects microwave energy.
• Heating Element: Provides heat for grilling.
• Metal Rack: Used for grilling.

Installation

1. Steady, flat location: Place the microwave oven on a steady, flat surface.
2. Leave space behind and side: Ensure adequate clearance for air vents to prevent overheating.
3. Away from radio, and TV sets: Position the oven away from TVs and radios to avoid interference.
4. Away from heating appliances and water taps: Keep the oven away from heat sources and water splashes.
5. Power supply:
   • Check local power source. Requires approximately 12 amperes, 230V 50Hz.
   • Use a receptacle with an earth prong.
   • Voltage Warning: Use only the specified voltage. Higher voltage can cause fire; lower voltage can result in slow cooking.
   • Power supply cord is approximately 1.0 meter long. Do not use an extension cord.
   • If the supply cord is damaged, it must be replaced by a qualified service person.
6. Examine the oven after unpacking: Check for damage such as dents, misaligned or broken doors, or cavity dents. Do not install if damaged.

Wiring Color Code:

• Green-and-yellow: Earth
• Blue: Neutral
• Brown: Live

IMPORTANT: Ensure wires are connected to the correct terminals in the plug based on their color and the terminal markings (E/green-yellow, N/black, L/red).

CAUTION: Do not remove the earthing prong. Maintenance on the power cable must be done by a qualified technician.

WARNING: This appliance must be earthed.

Operation

1. Connect the mains lead to an electrical socket-outlet.
2. Place food in a suitable utensil on the glass turntable. For grill mode, use the Metal Rack.
3. Shut the door firmly.
4. How to set each function:
   • MICROWAVE Cooking: Set the variable POWER SELECTOR to the desired power level (DEFORST, MED-HIGH, HIGH).
   • GRILL Cooking: Set the POWER SELECTOR to the (grill) position.
   • COMBI Cooking: Set the POWER SELECTOR to the (combi) position.
5. Set the time control by turning the timer knob. The oven will operate in the selected mode. If setting less than 2 minutes, turn past 2 minutes and then back to the desired time.
6. The oven turns off automatically when the timer reaches “OFF”.
7. Safety Door Interlock Switches: The oven will stop automatically if the door is opened during cooking. Close the door to continue.
8. Stopping Cooking: Turn the timer knob to “OFF”.
9. NOTE on GRILL mode: Avoid opening the door frequently. Do not touch the oven window or interior when hot. Use oven gloves or pot holders for the tray.

Cooking Utensils

Check utensil suitability for microwave use:

Notes:

• (1) Without metal parts or metal trims.
• (2) Some plastics are heat-proof only to certain temperatures.
• (3) Aluminium foil can be used to shield delicate areas of food.
• (4) Metal tins can be used in combination methods, but deep tins reduce efficiency.

Measurement of the Microwave Output Power

Procedure to measure microwave output power by monitoring water temperature rise:

1. Use the microwave oven at rated voltage and maximum power with 1,000±5cc of potable water.
2. Use a cylindrical borosilicate glass vessel (max. 3mm thickness, approx. 190mm diameter).
3. Ensure the oven and vessel are at ambient temperature. Initial water temperature: 10±2°C (50±3.6°F). Place the vessel on the lowest shelf position.
4. Switch on microwave power.
5. Heating time: 52 seconds at full power. Filament heat-up time is not included.
6. Select initial and final water temperatures so the difference between ambient and final water temperature is 5K.
7. Calculate power output (P) in watts using the formula: P = 4187 x ΔT/t, where ΔT is temperature rise and t is heating time.

The measured power should be 800W±10%.

CAUTION:

• Water load must be measured exactly to 1 liter.
• Input power voltage must be exactly 230 volts.
• Ambient temperature should be 20±2°C (68±3.6°F).

Diagram: Shows a glass vessel with water load on a tray inside the microwave cavity.

Microwave Radiation Test

WARNING:

• Check microwave leakage before and after repair.
• Measure unknown fields to ensure safety.
• Do not place hands in suspected radiation fields without knowing the safe density level.
• Avoid direct eye exposure to the microwave source.
• Approach the unit slowly with the radiometer until leakage is detected.

Procedure:

1. Prepare Microwave Energy Survey Meter, 600cc glass beaker, glass thermometer (100°C or 212°F).
2. Pour 275cc±15cc of tap water (20±5°C / 68±9°F) into the 600cc beaker (approx. 9.5cm / 3.5 in diameter).
3. Place the beaker at the center of the tray and set it in the cavity.
4. Close the door and operate the oven.
5. Measure leakage using the survey meter set to 2450 MHz.

Measured radiation leakage must not exceed 4mW/cm² for a fully assembled oven with the door normally closed.

Measurement points: Use the 2 in (5cm) space cone with the probe. Hold the probe perpendicular to the cabinet, door, door seam, door viewing screen, exhaust air vents, and suction air vents.

Measurement direction: Move the probe in a counter-clockwise direction at a rate of 1 inch/sec. Move more slowly if the cabinet door seam leakage is unknown.

Corner measurement: Keep the probe perpendicular to the areas, ensuring the probe end does not get closer than 2 inches from any metal to avoid erroneous readings.

Diagram: Shows a microwave oven with a probe being used to measure radiation leakage near the door seam.

Wiring Diagram

The document includes detailed wiring diagrams for the microwave oven, illustrating the connections between various components such as the transformer, magnetron, switches, and power supply. Color codes for wires are provided: RD (Red), WH (White), BK (Black), BL (Blue), GY (Gray), GN (Green), GE (Green/Yellow), BR (Brown).

Key components and their functions are indicated, including:

• TIMER ASS'Y
• SLOW ACTING RELAY ASS'Y
• V.P.C. (Variable Power Controller)
• HIGH VOLTAGE TRANSFORMER
• MAGNETRON
• H.V. FUSE
• H.V. CAPACITOR
• H.V. DIODE
• INTERLOCK SWITCHES (Primary, Secondary, Monitor)
• GRILL SELECTION SWITCH
• THERMOSTAT
• HEATER
• FAN MOTOR
• GEARED MOTOR
• CAVITY LAMP
• TIMER MOTOR

Conditions for operation are also noted, such as DOOR: CLOSED, TIMER: ON, SELECTION: MICROWAVE, V.P.C.: HIGH.

Circuit Description

The document describes the circuit operation in three stages:

1. When the food is placed in the oven cavity and door is closed: The interlock monitor switch (NO) opens, and the primary and secondary interlock switches close.
2. When the timer is set to the desired time: The timer switch closes, the oven lamp turns on, 230V AC is applied to the high voltage transformer, the turntable and fan motors start, and the timer motor operates. A 3.3 Volts AC is generated for the magnetron filament. A high voltage of 2000 Volts AC is generated and increased by the diode and capacitor to power the magnetron. Noise is suppressed by choke coils and filter capacitors.
3. When the door is opened during cooking: Primary and secondary interlock switches open to stop microwave oscillation. Fan motor, timer motor, and turntable motor stop. Oven lamp turns off. The monitor switch closes (NC) to create a short circuit. If interlock switches malfunction, the 15A fuse blows due to the surge.

Diagrams: Figure 1 shows the circuit when the door is closed and the timer is set. Figure 2 shows the high voltage circuit and the magnetron operation.

Precautions for Disassembly and Repair

Cautions:

• Microwave ovens are high-voltage, high-current equipment. Carelessness can lead to electric shock or danger from short circuits.
• Always remove the power plug before servicing.
• Use insulated screwdrivers and rubber gloves when working on the high voltage side.
• Discharge the high voltage capacitor before touching any components or wiring.

Specific Checks and Warnings:

1. Check the earthed connection: Do not use a two-wire extension cord. Ensure the oven is properly earthed.
2. Warning about electric charge in the high voltage capacitor: Electric charge remains in the capacitor for about 30 seconds after power off. Short the oven chassis to the negative high terminal of the capacitor using an insulated screwdriver to discharge it.
3. 15A Fuse: If the 15A fuse blows due to monitor switch operation, replace the primary, secondary interlock switch, and monitor switch. Refer to the next page for adjustment.
4. After repair: Ensure all screws and electrical connections are properly tightened.
5. Do not operate the oven without the cabinet.

CAUTION: Service personnel should remove watches when working near the magnetron.

WARNING: High potential parts (H.V. Transformer, Magnetron, H.V. Capacitor, H.V. Diode) can cause electrical shock or expose microwave energy.

Disassembly and Assembly

Instructions for disassembling and reassembling the microwave oven:

1. To remove cabinet: Remove three screws on the cabinet back.
2. To remove door assembly:
   1. Remove two screws securing the stopper hinge top.
   2. Remove the stopper hinge top and door assembly from the top plate of the cavity.
   3. Remove the stopper hinge top from the door assembly.
   4. Reverse the steps for reassembly, taking care to replace fixing glue.
3. To remove door parts: The diagram shows the door plate, barrier screen inner, door frame, spring, hook, and barrier screen outer. The steps involve removing these parts in sequence.
4. Method to reduce the gap between the door seal and the oven front surface:
   • Part 'A': Loosen two screws on the stopper hinge top, push the door to contact the seal, then tighten screws.
   • Part 'B': Loosen three screws on the bottom hinge, push the door to contact the seal, then tighten screws.
   • Part 'C': Loosen a screw on the bottom interlock switch assembly, draw the assembly inward to engage the hook, then tighten the screw.
   • Part 'D': Loosen a screw on the top interlock switch assembly, and follow steps for Part 'C'.
5. To remove control panel parts: Remove the screw securing the control panel, push snap fits, and draw the panel forward. Then, remove specific parts like the door open lever, timer assembly, timer knob, timer coupler, switch micro, V.P.C. coupler, V.P.C knob, door open button, and button spring. Reverse steps for reassembly.
6. To remove high voltage capacitor: Remove screws securing the grounding ring terminal of the H.V. diode and capacitor holder. Remove the H.V. diode from the capacitor holder. Reverse for reassembly.
7. To remove magnetron: Remove three screws securing the magnetron. Remove the magnetron. Reverse for reassembly.
8. To remove fan motor assembly: Remove screws securing the back cover and fan motor. Pull out the fan from the motor. Reverse for reassembly.
9. To remove transformer: Remove screws holding the H.V. transformer. Remove the transformer. Reverse for reassembly.
10. To remove insulator Heater assembly: Remove HEX nuts and the insulator heater assembly. Reverse for reassembly.
11. To remove Heater Part: Remove HEX nuts, insulator heater, heater, and screws. Reverse for reassembly.

Diagrams: Multiple diagrams illustrate the disassembly steps for the cabinet, door assembly, door parts, control panel, high voltage components, magnetron, fan motor, transformer, and heater assembly.

Interlock Mechanism

The door lock mechanism is designed to eliminate microwave radiation when the door is opened during operation.

1. Primary interlock switch: When the door is closed, the hook locks it and pushes the micro switch button, activating the primary interlock switch.
2. Secondary interlock switch and interlock monitor switch: When the door is closed, the hook pushes a lever that presses the monitor interlock switch (off) and the secondary interlock switch (on).

ADJUSTMENT 1 (Primary Interlock Switch):

• When the door is closed, the switch button is pushed by the hook.
• The switch button movement should exceed 1.2mm at the top.

ADJUSTMENT 2 (Interlock Monitor Switch & Secondary Interlock Switch):

• Interlock monitor switch: Should be opened before other switches close when the door is closed, and closed after other switches open when the door is opened.
• Secondary interlock switch: The switch button movement should exceed 1.2mm at the top.

Adjustment Steps:

1. Loosen the two mounting screws.
2. Adjust the interlock switch assembly position.
3. Confirm the 1.2mm gap.
4. Ensure smooth push lever movement.
5. Tighten the mounting screws.

NOTE: Microwave emission test should be performed after adjusting the interlock mechanism. If leakage exceeds 4mW/cm², readjust.

Interlock switch replacement:

1. Refer to the diagram.
2. Check the connection of the monitor switch after replacement.
3. Perform electrical continuity checks and microwave emission tests.

Diagrams: Show the interlock mechanism and adjustment points. A table lists switch symbols and their corresponding colors (RD, WH, BK, BL).

Trouble Shooting Guide

This section provides a flowchart for diagnosing common problems:

Trouble: Door shut, timer set but no cooking takes place.

1. Check: Does the fan motor work when the door is shut and timer is turned?
2. If NO: Check if the 12A fuse blows.
3. If fuse blows (YES): Replace primary, secondary interlock switch, and interlock monitor switch (all must be replaced simultaneously).
4. If fuse does not blow (NO): Check continuity of the interlock monitor switch with the door shut. If no continuity, replace the fuse. If continuity, proceed.
5. Check continuity of both interlock switches and monitor switch contacts with the door partially open until the monitor switch contact closes.
6. If both have continuity: Replace primary, secondary interlock switch, and interlock monitor switch.
7. If both have no continuity: Replace primary, secondary interlock switch, and interlock monitor switch.
8. If one has continuity and the other does not: Replace primary, secondary interlock switch, and interlock monitor switch.
9. Disconnect one lead wire from the transformer to the high voltage capacitor and operate the oven.
10. If fuse blows again: Replace the high voltage transformer.
11. If fuse does not blow (Normal): Replace the high voltage capacitor.
12. Check continuity of H.V.T. Thermal cut-out. If no continuity, replace H.V.T. Thermal cut-out.
13. Check continuity of power supply cord. If no continuity, replace the power supply cord.

Trouble: Does the fan motor work? Does the oven lamp light? Does the turntable turn?

1. If NO to any: Replace or repair the oven lamp or turntable motor.
2. If YES to all, but NO microwave oscillation:
• Check the relay contact of the slow acting relay assembly. If it does not operate, replace the slow acting relay assembly.
• Check continuity of the magnetron filament. If no continuity, replace the magnetron.
• Check continuity of the magnetron filament tap (3.3V) of the high voltage transformer. If no continuity, replace the high voltage transformer.
• Check the diode for continuity in reverse and normal directions. If NO GOOD, replace the high voltage diode.
• Check the isolation of the filament winding of the high voltage transformer. If GOOD, the magnetron is faulty; replace the magnetron.

Component Test Procedure

General Precautions:

• High voltage is present at the high voltage transformer terminals during cooking.
• Do not attempt to measure high voltage.
• Always unplug the oven and discharge the capacitor (see page 14) before touching components or wiring.

Component Tests:

1. High voltage transformer:
   • Remove connections and check continuity.
   • Normal readings: Secondary winding ≈ 120Ω ±10%, Filament winding ≈ 0Ω, Primary winding ≈ 0Ω.
   • Use an ohmmeter on the highest resistance scale. Measure resistance across diode terminals. Reverse meter leads. Normal diode resistance is infinite in one direction and several hundred KΩ in the other. Use a 6V or higher voltage battery for testing.
2. High voltage capacitor:
   • Check continuity with meter on the highest OHM scale.
   • Normal: Shows continuity briefly, then indicates 9MΩ (charged).
   • Shorted: Continuous continuity.
   • Open: Constant 9MΩ.
   • Resistance between terminals and chassis should be infinite.
3. High voltage diode:
   • Isolate the diode by disconnecting leads.
   • Measure resistance across terminals. Normal resistance is infinite in one direction and several hundred KΩ in the other.
4. Magnetron:
   • For complete diagnosis, refer to "Measurement of the Microwave Output Power" (Page 7).
   • Continuity checks can only indicate an open filament or shorted magnetron.
   • Isolate the magnetron by disconnecting leads.
   • Continuity check across magnetron filament terminals: should be ohm or less.
   • Continuity check between filament terminal and magnetron case: should read open.
5. Interlock monitor switch:
   • Isolate the switch. Connect meter to common (COM) and normally close (NC) terminals.
   • Meter should show open circuit with door closed, and closed circuit with door opened.
   • If improper operation, adjust or replace the switch.
6. Primary and secondary interlock switch:
   • Isolate the switch. Connect meter to common (COM) and normally open (NO) terminals.
   • Meter should show open circuit with door opened, and closed circuit with door closed.
   • If improper operation, adjust or replace the switch.

Safety Interlock Continuity Test

Disconnect the oven from the power supply. Test continuity of safety interlocks and monitor switch using a switch tester or ohmmeter. Switch operation is checked by lamp on/off (resistance zero/unlimited).

Test Sequence: Interlock monitor switch; primary and secondary interlock switches.

Circuits for tests:

1. In case of interlock monitor check: (Lamp on or zero resistance) Connect ohmmeter to common and normally closed terminals of the monitor switch. Condition: Door is opened. Common terminal of the monitor switch disconnected.
2. In case of primary interlock check: (Lamp on or zero resistance) Connect ohmmeter to common and normally open terminals of the primary interlock switch. Condition: Door is closed.
3. In case of secondary interlock switch: (Lamp on or zero resistance) Connect ohmmeter to common and normally open terminals of the secondary interlock switch. Condition: Door is closed.

Diagrams: Show test circuits (Fig. a, Fig. b, Fig. c) for each interlock switch. A schematic diagram of a S/W tester is also included.

Exploded and Parts List

This section provides detailed exploded views and parts lists for different assemblies of the microwave oven.

1. Door Assembly

The diagram shows the components of the door assembly, including the barrier screen, door frame, stopper hinge, door weld, gasket, hook, and spring hook. A parts list details the REF NO, PART CODE, PART NAME, DESCRIPTION, Q'TY, and REMARK for each component.

2. Control Panel Assembly

The diagram illustrates the components of the control panel, such as the door open button, button spring, knobs (VPC and Timer), control panel itself, lever door open, micro switches, tapping screws, coupler, and timer. A comprehensive parts list is provided with part numbers, descriptions, and quantities for various models.

3. Main Unit

A diagram shows the main unit with numerous numbered components, indicating their locations within the oven's internal structure.

Parts List: A detailed list of parts is provided, including PART NAME, PART CODE, DESCRIPTION, Q'TY, and REMARKS. This list covers a wide range of components from the door assembly to the main internal parts like the magnetron, transformer, capacitor, diode, fan motor, and various screws and fasteners.