R990K(W)
7 – 1
R990K(W)
Service Manual
CHAPTER 7. TROUBLESHOOTING GUIDE
[1] FOREWORD
When troubleshooting the microwave oven, it is helpful to follow the
Sequence of Operation in performing the checks. Many of the possible
causes of trouble will require that a specific test be performed. These
tests are given a procedure letter which will be found in the “Test Pro-
cedure”section.
IMPORTANT:
If the oven becomes inoperative because of a blown fuse F10A in the
upper latch switch - lower latch switch - monitor switch circuit, check
the upper latch switch, lower latch switch and monitor switch before
replacing the fuse F10A.
[2] CHART
MAGNETRON
POWER TRANSFORMER
H.V. RECTIFIER ASSEMBLY
HIGH VOLTAGE CAPACITOR
LATCH AND STOP SWITCHES
MONITOR SWITCH
DAMPER SWITCH
MAIN FUSE
TEMPERATURE FUSE 150C
THERMAL CUT-OUT
CONVECTION HEATER
THERMISTOR
FAN MOTOR
TURNTABLE MOTOR
CONVECTION MOTOR
DAMPER MOTOR
HIGH VOLTAGE FUSE
TOUCH CONTROL PANEL
KEY UNIT
RELAY (RY-1)
RELAY (RY-2)
RELAY (RY-3)
RELAY (RY-4)
RELAY (RY-5)
RELAY (RY-6)
FOIL PATERN ON P.W.B.
AH. SENSOR
OVEN LAMP OR SOCKET
O
PENED OR SHORTED WIRE HARNESS
WALL OUTLET
LOW POWER SUPPLY VOLTAGE
SHORTED POWER CORD
NOISE FILTER
CK = Check / RE = Replace
OFF
CONDITION
ABC
D
EE EFGGH I J J J J K MNOOOOOOPQRE CKCK CK RE L
COOKING
CONDITION
(MICROWAVE)
PROBLEM
CONDITION
TEST PROCEDURE
POSSIBLE CAUSE
AND
DEFECTIVE PARTS
(AH. SENSOR)
(CONVECTION)
Home fuse blows when power
supply cord is plugged into wall
outlet.
Fuse M8A blows when power
cord is plugged into wall outlet.
Oven lamp does not light with
door opened.
Oven lamp does not light at all
Cooling fan motor does not operate.
The oven stops after1 minute.
Oven lamp light, but turntable
motor does not operate.
Oven does not go into a cook cycle,
when START pad is touched.
Function of variable cooking does
not operate properly except
HIGH power.
Oven is in the sensor cook-ing
condition but AH sensor does not
end 1st. stage or does not stop
cooking cycle or the oven stops
soon.
CONV indicator lights, but
heating element does not heat.
Temperature in the oven cavity is
lower or higher than preset.
Convection cycle runs 1 minute
then the oven shuts down.
Convection cycle runs 3 min-
utes then the oven shuts down.
Extremely uneven heating is
produced in oven load (food).
Display does not show anything
when power cord is first plugged
into wall outlet.
Display does not operate properly
when STOP/ CLEAR pad is
touched. (The time of day should
appear on the display with beep
sound during normal condition.)
Low or no power is produced
during microwave cooking (The
food is heated incom-pletely or
not heated at all)
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