System Control Ic Input/Output - Tascam 122 Service Manual

16
-
.8
I
PLAY PLAY
12
IN
OUT
0603
6
PAuSE PAUSE
"
IN
OUT
R614
R616
3
F.F'NO F. FWD
I~
IN
OUT
5
REW
R[W
13
IN OU T
7
R[C R[C
1 0
IN
OUT
2
STOP FAST
"
IN
OUT
•
MEMO
$ 69!1 R622
IN
C607
AR
U601
e601 ""
C60~
O.OI/!>OV
C606 tOllOV
R610
,-----I------r----t--
CAPSTAN SOL. DRIVE CIRCUIT
,----Y>h---t--t-..
FAST SOL. DRIVE CIRCUIT
R627 t---t--
REC SIGNAL CONTROL CIRCUIT
0601 0604
0610 R623
R630
D605
0606
122
R621
R628 0604
RECORD LED __
~>M---II'!--
PAUSE LED
t5.3v
.--------------r---t-
PINCH ROLLER SOL. DRivE CIRCUIT
R629 ·
_
C607 O .O I/~OV
OV
~----------------4-------------------------------------4---4--0V
Fig. 3-3 System control
Ie
input/output circuits
3~.
SYSTEM CONTROL IC INPUT/OUTPUT
CIRCUITS
3-2-1 Initial reset circuit
See Fig. 3-3 .
The initial reset circuit generates a signal which
puts the deck in the stop mode immediately
after power is turned on, preventing incorrect
operation during the time the DC supply volt­
age is unstable.
1) When no cassette is loaded
When no cassette is loaded, cassette-in switch
S695 is set to N.O., which is the state entered
when the stop button is depressed. I n this
way the deck enters the stop mode when
power is turned on.
2) When a cassette is loaded
When a cassette is loaded, cassette-in switch
S695 is set to N.C. and isolated from the stop
circuit. If the power is turned on at this time,
current from system control IC U601 charges
the noise suppressing capacitors (C601 ­
C607) in the control input circuit of U601.
It takes approximately 20 msec to charge
C601 - C605 due to their low capacity.
When the capacitors are fully charged, the
PLAY, PAUSE, F. FWD, REW, and REC
input terminals switch to H level. It takes
approximately 100 msec for the STOP in­
put terminal (and MEMO input terminal) to
rise to H level since C606 has a large capacity.
In this way, of the operation input terminals,
only STOP takes longer to switch to H level.
As a result, a flip-flop is reset in U601 when
power is turned on and the deck enters the
stop mode.
Unless C606 is fully charged and the STOP
input terminal is at H level, U601 does not
switch from the stop mode to another mode
even if operation signals are input.
9