NAD 300 - Troubleshooting

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