Troubleshooti Ng - NAD 300 Service Manual

T,TROUBLESHOOTING
Symptom
1)
Fuse
blows
when power
is
turned on.
--
Power
Transformer T851 defective.
R
ep
lace
the transformer.
Short in
the primary or secondary of transformer
circuitry.
Repair
the short.
Damaged
rectifier D806, D805, D831, D832.
Replace
the
damaged
rectifier.
Short
circuit
in
the power transistor TR610,
TR611
,TR612,
TR613.
Replace
the defective transistor and check circuit.
Resistor
R811, R821 defective (open).
Replace
the defective resistor.
Capacitor C807, C809, C810
or CB14 defective.
Replace
the defective capacitor.
Open
in secondary winding of the power
transformer T851.
Replace
the transformer.
Transistor TR807 or TR810 damaged (open),
Replace
the
damaged
transistor.
Diode D803 or D804
damaged.
Replace
the
damaged
diode.
A)
B)
c)
D)
A)
B)
c)
D)
E)
2l
Pilot lamp
lights
but no sound
from
both
channels.
3)
"A"
Speakers
do not worl(.
A)
Speaker
switch S17 defective.
Replace
the switch,
4l
"B"
Speakers
do not work.
A)
Speaker
switch S17 defective.
Replace
the switch.
One
channel does
not work with
VOLUME at maximum
with
a
test
signal
applied
to the
center
terminal
of
VOLUME control VR551
of
the dead channel.
5)
A)
Defect in transistor TR901, TR902, TR903 or
TR904 of 9025 TONE AMP BOARD.
Locate and
correct the defect.
Defect in transistor TR751
,1R752 of
7105
SWITCH BOARD.
Locate and
correct the defect.
Defect in transistor
TR601-TR613 of
6038
MAIN AMP BOARD.
Locate and
correct the defect.
Break in
copper
foil of
printed circuit board
6038, 7105 or 9025.
Repair
the circuit board.
Short in speaker
output terminal.
Repair
the short.
B)
c)
D)
E)
14