Akai GX-77 Service Manual

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4)
Power
ON
-
Without any input conditions (such as operation
key is not pressed) through the built-in reset
circuit, IC] performs no operation. (In order to
meet the conditions for the operation of the built-
in reset circuit, 3 terminal regulator is used only
for the IC1 power source)
5) Loading Mode After Power ON
If
the
loading
operation
SW,
etc.
is
pressed,
the
output
of
ICI
enters
@)
through
TR3,
and
@8
(loader
plunger)
changes
from
“L”
to
“H”
(=
10V)
for
0.2
sec.,
TR35
and
36
“ON”
and
TR37
and
38
ON
through
D32,
and
+36V
is
added
to
the
loader
plunger.
Because
the
loader
plunger
is
ON
for
about
0.2
sec.,
the
loading
gear
starts
rotating
via
the
capstan
flywheel,
and
the
motor
SW
(SW903)
interlocked
with
it
will
be
ON
until
the
gear
finishes
one
turn,
and
then
TR22
to
TR25
ON,
and
the
voltage
(+S5V
under
no
load,
+3V
after
motor
loading)
is
added
to
the
right
and
left
reel
motors
which
turn
in
the
respective
winding
direction.
Thus
the
tension
is
added
to
the
tape
to
prevent
sagging
even
if
the
mechanical
brake
interlocked
with
the
loading
gear
is
released
during
loading.
The completion of loading is detected by SW905,
i.e,, the next operation is not available until the
SW905 is ON.
6) FWD Mode After Loading
20
With FWD key ON, the output of IC1 © is
inputted into @ and @ “L” > “H”, G8 “L” >
“H”, and then TR31, 32 ON, TR 22, 23 ON, and
the right reel motor rotates, FWD plunger is also
ON and the right pinch roller is pulled. The right
and left brakes mechanically interlocked with
the FWD plunger are released. The supply back
tension is added to the reel table by the brake pad
interlocked with the supply tension arm. (The
supply motor rotates freely). @9 (QT) is also ON
for 0.4 sec. and +36V is added to the plunger >
subsequently held at +14V.
With @4 (P.B. Mute) “H” > “L”, Mute will be
off.
7) REV Mode (reverse operation to FWD)
IC1 3 “H’ = left reel motor rotates
@) “H” > FWD plunger ON
@) “H” (for 0.4 sec.) > +36V > +14V
6) “L” > Mute Off.
8) FF Mode
IC1 @ (O FAST) “L” > “H”, TR26, 27 ON,
RL1 ON, and +12V is added to the reel motor,
® (right motor) “L” + “H”, TR22, 23 ON, and
the right reel motor rotates at a high speed. @
(brake plunger) “L” > “H”, TR31, 32 ON, brake
PLG ON, and the supply motor rotates freely
(the reel table is only receiving mechanical free
tension). @4 (PB Mute) is fixed at “‘H” and the
line output is cut off.
9) RWD Mode (reverse operation to FF)
IC! @ © FAST) “L” + “H”, RLI ON, +12V
applied
@ (brake plunger) “L” +> “H”, brake
released
G3 (left motor) “L” > “H”, left reel motor
rotates at high speed.
@) (PB Mute) fixed at “H”, and line output
cut off.
10) FWD/REC Mode
With the input IC1 © + @ and at the same time
IC1 © > @), the output of IC1, with FWD mode
output, @ “L” > “H”, TR39 ON, operates the
OSC circuit of the preamplifier. @3 “H” + “L”,
preamplifier TR17 OFF, TR18 ON, RL1 (Rec
Mute Relay) ON, and the preamplifier REC input
signal is added to the Rec head. @) “H” > “L”
and PB Mute released.
11) FWD, REV Direction (Refer to Fig. 21)
SWI — 2 (Pre Amp PCB) Signal from REV > FWD
SW.
If IC1 @ is “L” (REV mode), IC1 will be in
REV STANDBY mode, i.e., when IC1 @ is ON,
“L” + “H” + “L” is repeated 4 times > (REV
LED flashes 4 times) and then fixed at “H” +
(LED “ON”). (See the description of lighting
circuit operation).

Akai GX-77 Specifications

General

Track System	4-track, 2-channel stereo
Tape Speed	3 3/4 ips, 7 1/2 ips
Wow and Flutter	0.03% (19 cm/s)
Heads	3
Motors	3
Dimensions	440 x 244 x 358mm
Inputs	Line input (RCA)
Outputs	Line, Headphones