Akai GX-747 dbx Service Manual page 25

4-2-4 MICROCOMPUTER RESETTING CIRCUIT
(Refer to Fig. 6-39)
TR!57
N~
2SD794(P,O)
:g~
J901
~
I
BACK
UPI
A reset circuit is provided in order to eliminate
the memory of the electronic counter and 0
Stop when power is supplied.
When power is turned on, the voltage (+l0V)
is supplied to the base of TR54 through C44
and Rl64 to tum TR54 ON, i.e., the collector
of TR54 will be "L" to tum TR55 OFF
4-2-5 TIMER STARTING CIRCUIT
(Refer to Fig. 6-40)
J4 PRE AMP
PCB
t
IC? MCl4011BCP
Rl53 IOK
3
IC7 OV :I!
2 -~
.,.,
UN
.,;
!I!
a:
..,:.:
..,o
_,._
a::"'
Rl5!5
82K
TR!51 2SC94!5L ( P,O)
When TIMER REC:
When power is switched ON, the base of TR5 l
is turned "H'' through C49 and R88 of the Pre
Amplifier P.C Board and through D54 and
R158 of J17
@
of the Syscon P.C Board.
The collector becomes "L" to tum TR63 ON
throu~ R205. The "H" from J1 7
@
makes
IC7
~
"H" through D53, Rl 55 and R1·56,
and at the same time, "H" is supplied to IC7
@
through D53, R152 and Rl53. Depending
on the condition of the collector of TR96, the
output to IC7
@
or IC7
@
is determined
+1ov
to
1c1,2(V
Fig. 6-39
through Rl 68 which means the collector of
TR5 5 will be "H". Then "H" is supplied to
Terminal
(j)
of ICl and 2, and when Terminal
(j)
becomes "H", the microcomputer is reset.
When the charging to C44 is completed, TR54
is turned OFF, TR55 ON and Tenninal
(j)
"L".
TR96 2SA7331AHPO)
Rl52
82K
"'
!
!
,,,,._
..,..,
ON
a,
0N
..,
.....
"'
!!?
u"!
iE
"'
TR97 2SC94!5L ( P,Q)
Fig.
6-40
and the direction of FWD or REV is de-termin-
ed. If the collector of TR96 is "L", IC)
G)
be-
comes "H".
Therefore, "H" goes into IC7 (}) and(§) , the
IC7
@
becomes "L".
TR60 is energized through D56, i. e.,, FWD
REC.
When TIMER PB:
Same as for REC TIMER START, but due to
the lack of input in TR51, FWD or
REV
PB is
achieved instead of REC.
- - - - - - - - - - - - - - - - SERVICE MANUAL GX-747dbx - - - - - - - - - - - - - - - -
24