Circuit
diagram, Wiring Diagram, Fault finding – Daewoo KOC154K9A27 Microwave oven
COMPONENT
TEST PROCEDURE
High
voltage is present at the high voltage terminal of the high voltage transformer
during any cooking cycle.
It
is neither necessary nor advisable to attempt measurement of the high voltage.
Before
touching any oven components or wiring, always unplug the oven from its power
source and discharge the capacitor.
High
voltage transformer
1) Remove connections from the transformer terminals and check continuity.
2) Normal readings should be as follows :
Secondary winding ... Approx. 100 Ω ±10%
Filament winding ... Approx. 0.1 Ω
Primary winding ... Approx. 1.4 Ω
1) Remove connections from the transformer terminals and check continuity.
2) Normal readings should be as follows :
Secondary winding ... Approx. 100 Ω ±10%
Filament winding ... Approx. 0.1 Ω
Primary winding ... Approx. 1.4 Ω
2. High voltage capacitor
1) Check continuity of capacitor with meter on the highest OHM scale.
2) A normal capacitor will show continuity for a short time, and then indicate 10MW once the capacitor charged.
3) A shorted capacitor will show continuous continuity.
4) An open capacitor will show constant 10MΩ .
5) Resistance between each terminal and chassis should be infinite.
3. High voltage diode
1) Isolate the diode from the circuit by disconnecting the leads.
2) With the ohmmeter set on the highest resistance scale measure the resistance across the diode terminals.
Reverse the meter leads and again observe the resistance reading. Meter with 500KOhms or higher range. batteries should be used to check the front-back resistance of the diode, otherwise an infinite resistance may be read in both directions. A normal diode's resistance will be infinite in one direction and several hundred kΩin the other direction.
1) Check continuity of capacitor with meter on the highest OHM scale.
2) A normal capacitor will show continuity for a short time, and then indicate 10MW once the capacitor charged.
3) A shorted capacitor will show continuous continuity.
4) An open capacitor will show constant 10MΩ .
5) Resistance between each terminal and chassis should be infinite.
3. High voltage diode
1) Isolate the diode from the circuit by disconnecting the leads.
2) With the ohmmeter set on the highest resistance scale measure the resistance across the diode terminals.
Reverse the meter leads and again observe the resistance reading. Meter with 500KOhms or higher range. batteries should be used to check the front-back resistance of the diode, otherwise an infinite resistance may be read in both directions. A normal diode's resistance will be infinite in one direction and several hundred kΩin the other direction.
4.
Magnetron
For complete magnetron diagnosis, refer to "Measurement of the Microwave Output Power." Continuity checks can only indicate and open filament or a shorted magnetron. To diagnose for an open filament or a shorted magnetron,
1) Isolate magnetron from the circuit by disconnecting the leads.
2) A continuity check across magnetron filament terminals should indicate 0.1 Ωor less.
3) A continuity check between each filament terminal and magnetron case should read open.
5. Fuse
If the fuse in the primary and monitor switch circuit is blown when the door is opened, check the primary and monitor switch before replacing the blown fuse. In case the fuse is blown by an improper switch operation, replace the defective switch and fuse at the same time. Replace just the fuse if the switches operate normally.
For complete magnetron diagnosis, refer to "Measurement of the Microwave Output Power." Continuity checks can only indicate and open filament or a shorted magnetron. To diagnose for an open filament or a shorted magnetron,
1) Isolate magnetron from the circuit by disconnecting the leads.
2) A continuity check across magnetron filament terminals should indicate 0.1 Ωor less.
3) A continuity check between each filament terminal and magnetron case should read open.
5. Fuse
If the fuse in the primary and monitor switch circuit is blown when the door is opened, check the primary and monitor switch before replacing the blown fuse. In case the fuse is blown by an improper switch operation, replace the defective switch and fuse at the same time. Replace just the fuse if the switches operate normally.
PRINTED CIRCUIT BOARD Circuit Diagram (Schematic) Click on the pictures to magnify
Wiring Diagram
CIRCUIT
CHECK PROCEDURE
1. Low voltage transformer check
The low voltage transformer is located on the P.C.B.
Measuring condition: Input voltage: 120V / Frequency: 60Hz
1. Low voltage transformer check
The low voltage transformer is located on the P.C.B.
Measuring condition: Input voltage: 120V / Frequency: 60Hz
NOTE
1. Secondary side voltage of the low voltage transformer changes in proportion to fluctuation of power source voltage.
2. The allowable tolerance of the secondary voltage is within ± 5% of nominal voltage. [Each measure point must be measured with GND points.]
1. Secondary side voltage of the low voltage transformer changes in proportion to fluctuation of power source voltage.
2. The allowable tolerance of the secondary voltage is within ± 5% of nominal voltage. [Each measure point must be measured with GND points.]
Case
of no microwave oscillation
1) When touching M/W button, oven lamp turns on and Fan motor and turntable rotate, and cook indicator in display comes on.
*Cause: RELAY 1 does not operate.
1) When touching M/W button, oven lamp turns on and Fan motor and turntable rotate, and cook indicator in display comes on.
*Cause: RELAY 1 does not operate.
2)
When touching M/W button, oven lamp does not turn on and turntable motor does
not rotate but cook indicator in display comes on.
*Cause: RELAY 6 does not operate.
3)
When touching M/W button, oven lamp turns on and fan motor does not rotate but
cook indicator in display comes on.
*Cause: RELAY 7 does not operate.
*Cause: RELAY 7 does not operate.
4.
Case of no heating of upper grill
When touching GRILL1 & COMBI button, oven lamp turns on and Fan motor and turntable motor rotate and cook indicator in the display comes on.
*Cause: RELAY 4 does not operate.
When touching GRILL1 & COMBI button, oven lamp turns on and Fan motor and turntable motor rotate and cook indicator in the display comes on.
*Cause: RELAY 4 does not operate.
5.
Case of no heating of lower grill
When touching GRILL2 & COMBI button, oven lamp turns on and Fan motor and turntable motor rotate and cook indicator in display comes on.
*Cause: RELAY 9 does not operate.
When touching GRILL2 & COMBI button, oven lamp turns on and Fan motor and turntable motor rotate and cook indicator in display comes on.
*Cause: RELAY 9 does not operate.
6.
Case of no heating of convection grill
When touching CONVECTION button, oven lamp turns on and Fan motor and turntable motor rotate and cook indicator in the display comes on.
*Cause: RELAY 3 does not operate.
When touching CONVECTION button, oven lamp turns on and Fan motor and turntable motor rotate and cook indicator in the display comes on.
*Cause: RELAY 3 does not operate.
7.
Case of no stopping of the count down timer
When the door is opened during operation, the count down timer does not stop.
When the door is opened during operation, the count down timer does not stop.
