Akai GXC-750

. DURING TAPE TRAVEL
(Refer to Fig. 39)
1) During tape travel (recording, playback rewind, or
fast forward) the tape counter rotates. A magnet
also rotates according to tape counter revolutions
and turns a read switch ON «> OFF.
2) As the read switch is repeatedly turned ON <>
OFF, syscon circuit condenser Cl is charged and
discharged repeatedly.
3) Accordingly, an A.C. signal pulse is generated at
the anode side of Diode D1, and is rectified by
D1. This pulse is smoothed at condenser C2
and becomes the base bias of transistor TR3.
For this reason, TR3 is maintained at “ON”
during tape travel.
4) Transistor TR3 collector becomes about the same
electrical potential as ground, transistor TR6 base
is reverse biased by means of Diode D4 and
transistors TR6 and TR7 are maintained at “OFF”
during tape travel.
5) Because TR7 is held at OFF, also stop plunger
solenoid SL1 connected to the collector does not
function.
6) Therefore, during tape travel, the syscon circuit
works to hold stop plunger solenoid SL1 at OFF
condition.
. OPERATION WHEN READ SWITCH IS
“ON” AND TAPE TRAVEL IS STOPPED
(Refer to Fig. 40)
1) When the read switch is ON and tape travel stops,
the electric charge charged at condenser C1 passes
the read switch, and resistor R14 and is discharged.
2) Consequently, the anode side of diode D1 is
negative biased and Transistor TR3 base bias
becomes zero.
3) At the same time, transistor TR3 is turned OFF,
diode D4 is reverse biased, and bias is supplied to
transistor TR6 through resistor R11 and diode
D6 and TR6 and TR7 are both turned ON.
4) A D.C. current flows to plunger solenoid SL1
which is connected to the collector of transistor
TR7 as load and the plunger is pulled.
5) Thus, mechanism system operation begins accord-
ing to deck mode (stop, reverse, or Fwd).
6) At the same time that stop plunger solenoid SL1
functioned, a charge current begins to flow to
condenser C6 through resistor R12.
7) Condenser C6 charge current advances and when
the terminal voltage increases to slightly more than
the base cut-ff voltage, TR5 collector current
begins to flow and condenser C5 commences
discharge. As discharge advances, diode D6 anode
is reverse biased.
8) Consequently, transistors TR6 and TR7 are turned
OFF. (This TR6 and TR7 reverse operation time
is extremely short).
. OPERATION WHEN READ SWITCH IS
“OFF” AND TAPE TRAVEL IS
STOPPED. (Refer to Fig. 41)
1) When the read switch is OFF and tape travel
stops, a charge current begins to flow from
resistor R6 through condenser C1 to resistor R14
and C1 becomes charged.
2) While charge current is flowing to condenser Cl,
a drop in voltage at R14 occurs, but this does
not continue after charge to C1 is completed.
3) Consequently, the anode of diode D1 becomes
unbiased, and the base bias of Transistor TR3
also becomes non-existent.
4) Thus, at the same time, TR3 is turned OFF and
the same operation described in items 2-3) through
2-8) above takes place.
5) Therefore, regardless of the condition of the read
switch, when tape travel stops, the syscon circuit
functions and the mechanism system begins to
operate.
. MEMORY WIND OPERATION
As shown in Fig. 42, there is a switch inside the
tape counter which makes contact when the tape
counter scale reaches “900” and separates when the
scale reaches “O00”. Memory Wind Switch SW19
is thus turned ON, and when the scale reaches “000”’,
the syscon circuit operates and the deck enters
STOP mode.
OPERATION DURING REWIND (Refer to Fig. 42)
1) At RWD mode, syscon condenser C3 is charged
(resistor R18 —» condenser C3 —> resistor R21)
and bias is supplied to the base of transistor TR2
and TR2 is held at ON condition.
2) When the decreasing tape counter scale becomes
“000”, the contact point inside the tape counter
which was momentarily activated at “999”, makes
contact and the electric charge (charged at con-
denser C3) passes resistor R21 and as shown in
Fig. 42, discharge begins.
3) As condenser C3 begins to be discharged, the
voltage at point (a) increases and becomes
minus and the anode side of diode D3 is minus
biased.
4) Consequently, transistor TR3 is turned OFF and
stop plunger solenoid SL1 operates and the deck
enters STOP mode in the same way as is explained
in Section VIII, Item 1,1).
i