LG MB-3949G Service Manual page 24

(TROUBLE 2) Oven does not start cooking even though the timer is set and START pad
is touched.
CONDITION
1. Oven does not
start cooking
count down when
touching START
pad.
2. Fan motor or
oven lamp
do not turn
on.
(TROUBLE 3) Oven seems to be operation but little heat is produced in oven load.
CONDITION
Output is low.
NOTE: Simple test of power output-conducted by heating one liter water for one min. if available.
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Only for training and service purposes
CHECK
Check continuity
of secondary
switch (with
door closed).
Check the con-
nection between
connector and
P.C.B assembly.
Check fan motor.
Check oven lamp.
CHECK
Check the
power source
voltage.
Disconnect the
wire leads from
relay 2 and check
on and off time
with multitester.
Measure the
output power.
RESULT
Defective
No continuity.
secondary switch.
continuity.
No continuity.
Continuity.
Abnormal.
Abnormal.
Normal.
RESULT
Lower than 90% of
Decrease in power
rating voltage.
source voltage
with load.
Normal.
Defective P.C.B
Abnormal.
assembly.
Normal.
Abnormal.
5-14
CAUSE
Replace
secondary switch.
Defective P.C.B
assembly.
Loose connection.
Defective fan
motor.
Defective oven
lamp.
CAUSE
Suggest customer
contact local
electric power
utility co. or
qualified
electrician.
Replace P.C.B
assembly.
Defective Replace
magnetron. magnetron.
REMEDY
Replace P.C.B
assembly.
Connection then
tightly.
Replace fan
motor.
Replace oven
lamp.
REMEDY
LGE Internal Use Only