Service manual
of
main
board
No.
1
and
observe
voltage
drop
across
keyboard.
b)
Adjust
keyboard
trimpot
R79
(Figure
4-3)
for
a
voltage
indication
of
+9.000
V
+10
mv.
4.2.4
TRIGGERING
a)
Connect
oscilloscope
to
the
collector
of
Q8
(Figure 4-3)
and
verify
that
the
trigger
voltage
wave
form
present
is
as
shown
in
Figure
4-4
with
a
single
key
depressed.
b)
Hold
one key
down,
depress
next
higher
key
and
verify
that
a
retrigger
occurs.
+9V-
OV-
KEY
DOWN-*
-20
MSEC
KEY
UP—
FIGURE
4-4
TRIGGER
ATCOLLECTOR
OF
Q8
4.2.5
KEYBOARD
DRIFT
a)
Connect
DVM
to emitter
of
Q2
(Figure
4-3)
and
verify
the
keyboard
pitch
voltage
ranges
from
-4.50
V
+100
mv
at
the
lowest
key
to
+4.50
V
+100
mv
at
the
highest
key.
b)
Verify
that
the
pitch
voltage
holds
steady
while
a
key
is
being
depressed
and
after
the
key
is
released.
In
neither
case
should
the
drift
exceed
25
mv
per
minute.
4.2.6
PREPARATION
FOR
OSCILLATOR
A
TUNING
(MAIN
BOARD
NO.
1)
a)
Place
all
tab
switches
and
slide
controls
up,
turn
all
potentiometers
counterclockwise
and
place
VIOLIN
tab
switch
down.
b)
Connect
a
jumper
between
the
collector
and
base
of
Q3
(Figure
4-3)
in
order
to
keep
IC10
on
and
thereby
eliminate
keyboard
control
voltage
drift.
c)
Hold
down
the
middle
B(,
key
(14
semitones
below
topmost
key)
for
oscillator
A
tuning.
d)
Center
the
rear
panel
TUNE
control,
connect
wiper
to
ground,
place
1
OCT
tab
switch
down
and
connect
DVM
test
leads
between
pin
6
of
IC8
(bot
tom
of
R14,
Figure
4-3)
and
ground.
Adjust
range
trimpot
R16
for
an
indication
of
0.0000
+0.0001
V.
4.2.7
OSCILLATOR
SCALE
1
OCT
tab
switch
down
2
OCT
tab
switch
down
a)
Adjust
REF
frequency
for
zero beat
with
oscillator
A.
Normally
the
REF
frequency
will
be
between
430
and
500
Hz
and
the
Synthesizer
fre
quency
will
be
two
octaves
lower
(nominally
117
Hz).
b)
Hold
down
high
Bb
key
(highest
black
key)
and
zero
beat
oscillator
A
with
REF
frequency
using
scale
trimpot
R17
(Figure
4-3,
Synthesizer
=*
233
Hz,
1
octave
below
REF
frequency).
4.2.8
OSCILLATOR
A
HIGH
FREQUENCY
COMPENSATION
1
OCT
tab
switch
up
2
OCT
tab
switch
up
a)
Adjust
REF
frequency
to
zero
beat
with
oscillator
A
(Synthesizer
=*
932
Hz, 1
octave
above
REF
frequency).
b)
Hold
down
the
high
B(,
key
and
zero
beat
oscillator
A
with
the
REF
frequency
using
the
oscillator
A
high
frequency
trimpot
(Figure
4-3,
tacked
on
to
the
left
of
R21).
Repeat
steps
a
and
b
several
times.
27