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9.4 SYSTEM CONTROL INPUT CIRCUIT
a. Key Input Circuit
The key input consists of 8 strobe outputs and 4 return in-
puts connected in matrix, however, it is actually 7 x 4 be-
cause the pin #23 (D6) is left unused. This strobe signal
(DO-D7) is put out in the timing shown in Fig. 25. When the
TUNER button is depressed, S25 turns on. The #25 (DO)
output is fed to the pin #44 (R3) via D12, S25 and R134.
Then, PD4050B sends a command to PD4046B in the tuner
circuit and activates the tuner circuit. At this time, PD4050B
puts out a 3.8kHz square wave signal from the pin #49
(BUZZER)
for 30ms
to inform that it has accepted the
TUNER-ON
key input.
As this signal is 5V and is not strong enough to drive piezo-
electric buzzer (X1) directly, it goes to O35 via R130, turns
Q35 on and off for 30ms and is amplified to 8.5V and drives
the buzzer. Then a ''beep'' sound is generated every time
the key input is accepted. If there is trouble in the above cir-
cuit, no sound will be generated even though the key is
depressed.
Zener diode D30 (Vz: 20V) is to absorb the
..counter-electromotive force generated in the buzzer.
AOS
—
|
D1
2012S
b. Door Sense Input (Q2)
PD4050B senses the state of the door with this circuit as
this model has no exclusive EJECT key (button). A key is
commonly used for opening and ejecting. So, PD4050B has
to determine whether to open the door or eject the tape
when OPEN (S20) is depressed. This circuit feeds PD4050B
with a signal to open the door when it is close and to eject
the tape when it is open.
When the door is closed, $26 is closed. Q1 and Q2 are off.
Then, the signal from #24 (D7) to #44 (R3) is blocked.
When the door is open, S26 opens, Q1 and Q2 turn on, and
the signal is fed to #44 (R3).
c. Remote Control Input Circuit
A remote control signal selects a function by activating the
transistor connected in parallel to the tact switch of a par-
ticular function in the Switch Unit. But the remote controller
does not have the functions of command buttons (0) — (5).
So PD4050B selects the mode (0) when Q53 (MS/CH) is
turned on. When
Q53 (MS/CH) turns on once, PD4050B
recognizes the signal as (0). When it turns on twice suc-
cessively, the IC recognizes it as (1), three times, as (2), and
so on.
D7
me 3200S 7
|
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Fig. 25 Strobe signal timing
20
30
033
ia
CLOCK
Ss
aX
(4.2v
Ri27
a1V
D32
ate
DOLBY
NR B
set
DOLBY
NR C
ass
ae
C45
Rial
Z
ACC+B14.2v
Oo
S26
DOOR
SWITCH
CLOSE
: ON OPEN
| OFF
R2t
REMOTE
CONTROL
INPUT
c2t
aa
22
Zl
You
'fea
a
MS CH
Yo
eeee
a
Fig. 26 System control input circuit
"
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