Akai GX-747 dbx Service Manual page 23

Truth table of IC 1 Pins@and@in accordance with tension ann positions
@Pin
L
H
L
L
L
ICI
31
I
_ _ _ _ .J
(19)
Pin
L
L
L
H
L
Function mode
lndlcotor
4-2-3 FUNCTION MODE INDICATOR CIRCUIT
AND COUNTER CIRCUIT
• Function Mode Indicator Circuit
The function mode indicator lighting is also
controlled by the operation timing of the
control signal from the microcomputer.
Here we will explain about the situation in Fig.
6-37. (FWD PLAY/PAUSE) as one example.
Hereinafter FWD PLAY is just written as PLAY.
Under PLAY/PAUSE, PAUSE of the function
mode indicator is always is lit and PLAY is
flashing. Firstly, refer to the vertical raw of the
function mode indicators of 00 -03 in Fig. 6-37.
You will note that PAUSE IND has "H" level,
PLAY IND has "L/H" flashing and others have
"L" level.
The signals of (00 - 03) and IC
@
enter IC3
and IC4 and TR83 in Fig. 6-36. In this way the
digits of the function mode ind. and PLAY/
PAUSE IND. are inputted. When these two
digits are synchronized, the indicator is lit.
Lock
.j, Play key is pressed
Middle
.j, Shut-off
Lock
Fig. 6-35
COUNTER PCB
TI009C2550
• Counter Indicator Circuit
Fig. 6-36
The counter indicators are also lit by the pulse
from the microcomputer, and it is not that all
the indicators are always lit.
Because of the afterimage, it appears to our
eyes that all the digits are lit despite the fact
that they are lit in sequence as shown in Fig.
6-38. This system is called dynamic lighting
system.
Fig. 6-37 shows the timing chart. By ['leans of
the waveforms of IC@-@ coming from the
microcomputer, the lighting position or LED of
each digit is moved in sequence. T~e the
example of the first digit.
The first digit can only be lit when tl>.e wave-
form of IC
@
is "H" level. Dependii1B on the
condition of 00 - 06 at the time of
'H"
level,
each segment is lit and the figure is in.dicated.
Since the segments of the LED in'1icators
are cathode common, each segment is[jt when
00 - 06 are at
"H"
level. If we see He condi-
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