Control Board - Roland MicroComposer MC-4 Service Notes

CONTROL BOARD
DOT display/
SHIFT LEDs.
KEY SWITCHES
These
circuits
^re
configured in
separate matrices
in a
conyenlional
fashion
but
one dimension of
these share the same output pins
of an
address
decoder 1C1.
The address
decoders (IC1
and IC2
in
combination) places
an I
at
output pins
in
sequence in
symathy with
NM1
cIogI<
brought into th^
pin
€f
CPU
as
shown in Fig. 7.
The following description will
explicate
Dot Display
only since Shift
UEDs- and KEY- scanning are self
explanative,
^...p \
PCS (23} Q
ADDRsi
PC2<21)
Q Q
PCI
[19)
D
1
1
PC^[17|
10
1 Fig,
7
DOT DISPLAY
Character signal consistirig
of
& x 7 dots
from
the
Dot Matrix
Decoder
IC9
is
applied to fluorescent
lamp
indicator
16'MD-02Z
In
which the
same dots
in
the Individual digits
are
connected
in
parallel
and led
out
as a
common
terminal,
and the
digit
electrodes
have
indtvldual leads
(G1-G15) for
externa! connection.
Although the same dot signals are fed
to
all
digits
simaltenousiy,
only
one
digit
whose
grid is
now H
is
allowed to illuminate
-
called
dynamic
lighting.
But for
human
eyes those flickers
are
not perceptible.
Since filament laid
across the
tube serves
as
a
common
cathode for all
digits,
DC
heating
will
cause brightness
imbalance
among
digits
due
to
potential variations
between el&ctrodes
and the
chathode.
METRONOME
Output from
oscillator
IC7
is
shaped
into
metronome-lick sound with
percussive
envelope developed
In
Tr35,
C5 and R1 16 circuit.
TEMPO CLOCK GEMERATOR
When
nothing
is
connected to the
TEMPO CV
jack,
a
constant
DC
voltage of
approximately 4.17V
is
applied to pin 5 of tC6
when the
TEMPO
control
is
set at
the
center.
The
voltage
is
applied to the
VCO
through 106 and IC5, and the
VCO
oscillates at
approximately
lOOKHz,
Since the VCO's oscillation
frequency changes linearly to
the input
voltage,
when the input voltage
is
doubled, the oscillation
frequency
is
also
doubled.
When
the linearity
is
improper {especially at
the high
frequency range),
the slew rate of
IC3
is
slow or
TR31
is
defective
in
most
cases.
When
an external
CV
is
applied to the
TEMPO CV
IN jack, the
TEMPO
CLOCK
is
subjected to
frequency modulation.