Adjustment Procedure - Korg MS-20 Service Manual

KORG
MS-20
7.
ADJUSTMENT PROCEDURE
7-1
Power sup
ply
check
1
.
Positive lippte.
Should be
no
more
than
2mVp-p,
Set oscilloscope
vertical
gain
at
lOmV/cm
end
check
that
power
supply
ripple
is
2mV
or
less.
2.
Negative
ripple.
Same
as
positive,
should be
no more
tharv
2mVp-pH
7-2. Pitch
adjustment
1,
VCO-1.
Perform adjustment
with synthesizer controls at
"normal
setting"
(Scale =8,
Waveform—
fU
.
Master Tune.
Pitch, artd
all
other
knobs
at
"0'%
See
figure
1
.
a.
Play
C-4
(high
C) on
the
keyboard and
ad-
just
the high
O
sernl -fixed
screw
until
you
obtain
the correct
tuning as indicated
by
WT-10A
(connected lolheSIG
OUT
jack).
b.
Play
key C-1 and
adjust the low
^
semi'
fixed
screw.
0
.
Repeat
steps
a
and
b as
many
times as
necessary
until
both are
tuned
to
the correct
pitch.
d.
Check
the tuning
of
C*1, C-2, G-3,
and G-4
on the
WT-10A
meter
to
make
sure
pitch
devia-
tion
is
within
±2
cents
for
each.
e.
Change
the
scale
to
32\
1
6", 8',
and 4' and
check the tuning
of
all
four
C
keys
to
make
sure
that
the pitch deviation of
each
Is
within
+
1
0
cents.
2.
VCO-2.
Set the
VCO-1
level
at
and
the
VCO-2
level
at '"10". Then
follow the
same
procedure
as
for
VCO-1. by
adjusting
the high
and
low
semt'fixed screws.
7-3.
KSDCV
adjustment
Use a 4-1/2
digital
voltmeter
to
measure
the
K6D
CVOUT
signal.
a.
Measure
output vottage
first
when
you
play
key
C-4, then
when
you
play
key
C-3.
The
output
voltage
for
C-3
should be
exactly
halt that for
C-4. Adjust the
KBD CV
high
0
semi-tixed
screw
as necessary so
that
C-3 produces
half
the vottage
of C-4.
b.
Measure C-2 and
then
C-1
in
the
same
way.
Adjust the
KBD CV
low
0
semi-fixed
screw as
necessary so
that
C-2
produces
exactly
half
ihe
voltage ot
C-4.
c.
Repeat
steps
a
and
b
as
many
times as
necessary
until
the output voltage
of
each
of
C-1, C-2. C-3.
and C-4
is
exactly half that of the
next.
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WT-10A
DIGITAL
VOLTMETER
Fig.
1
7-4.
VCF
Fc adjustment
Ck>nnect
a frequency counter
to
the
PHONES
jack
(since a high
output
level
es
needed
tor
measure-
ment). Set
VCO-1 and VCO-2
level
at
"0^
1.
VCHPF
Refer
to
the
settings
shown
in
figure
2,
Set
the
LPF
PEAK
knob
at "0'\
and
the
HPF PEAK
knob
at
"10".
Then
adjust the
O
semi-fixed
screw as
necessary so
that the
HPF
oscillation
frequency
is
500Hz.
2.
VC
LPF
Set
HPF PEAK
at '
0".
and
LPF
PEAK
at
"10",
Then
adjust the
6
semi-fixed
screw
in
the
same
way
as you
did
for
the
HPF.
FREQUENCY
COUNTER