Service manual
TROUBLESHOOTING
GUIDE
(Cont.)
SYMPTOM
PROBABLE
CAUSE
7.2
SOUND
CHAIN
(Cont.)
E.
No
oscillator
B
output,
oscillator
A
operating
properly.
F.
No
oscillator
A
output,
oscillator
B
operating
properly.
G.
No
waveshaper
output.
H.
Band
pass
filter
will
not
pass
signal.
I.
J.
K.
Band
pass
filter
current
sources
at
fault.
Low
pass
VCF
and
VCA
do
not
pass
signal
(no
signal
on
pin
1
of
IC20).
L.
Low
pass
VCF
operating
properly
(proper
signals
at
pins
7
and
10
of
IC20)
but
VCA
has
no
output
(pin 1
of
IC20).
VCA
operating
properly
but
has
no
output.
1.
IC501,
IC502,
Q501,
Q502
or
Q503
defective.
2.
Input
wire
to
board
No.
5
broken.
3.
Resistor
R501
broken.
4.
Connector
pin
M,
R
or
P
shorted.
5.
IC11
defective.
1.
IC12,
Q43,
Q44,
Q45
or
Q46
defective.
2.
Open
OSC
A
HI
END
trimpot.
3.
Capacitor
C38
shorted.
1.
IC13,
Q47
or
Q48
defective.
2.
Resistor
R47
open.
3.
Faulty
wiring
to
pin
D6
of
resistor
matrix.
1.
Ground
collectors
of
Q38
and
Q39.
If
signal
still
does
not
pass,
trouble
is
in
IC15, IC16,
IC17,
Q41
or
Q42
or
associated
circuitry.
If
signal
passes
the
filter,
check
filter
control
current
sources.
1.
Remove
one
short
and
then
the
other
to
determine
which
transistor
pair,
Q37
and
Q38
or
Q39
and
Q40,
is
faulty.
2.
Ground
both
transistor
bases
of
the
faulty
pair
and
observe
if
signal
passes
(collectors
not
shorted).
If
signal
passes,
the
fault
lies
in
the
summing
network,
matrix
or
matrix
interconnecting
wiring.
Otherwise
the
transistor
pair
or
trimpot
is
at
fault.
1.
Short
pin
14
of
IC19
to
ground.
If
signal
passes,
the
fault
is
in
either
the
filter
contour
circuitry
or
the
transistor
the
collector
of
which
is
tied
to
pin
14.
If
signal
still
does
not
pass,
proceed
with
step
2.
2.
With
pin
14
of
IC19
still
shorted
to
ground,
measure
waveform
at
pins
7
and
10
of
IC20.
Signal
at
each
pin
should
be
approximately
10
mv
peak-to-peak
(about
hah'
the
20
mv
peak-to-peak
observed
at
pin
2
of
IC19).
If
signal
is
present,
VCF
is
operating
properly
arid
the
problem
lies
within
the
VCA.
If
signal
is
not
present,
trouble
is
in
IC19.
1.
Hold
down
a
key and
check
that
voltage
at
pin
12
of
IC20
holds
at
approximately
+3.5
VDC.
If
voltage
holds,
trouble
is
in
IC20,
R164,
VOLUME
control
R13
or
wiring
from
R164
to
R13.
If
voltage
at
IC20
does
not
rise,
the
amplitude
envelope
generator
is
not
functioning.
1.
Trouble
is
in
IC22,
C32,
LEVEL
ADJUST
control
R238
or
output
wiring.
39