Akai GXC-570D

netic braking to the proper motor when stop mode
is being effected from Fast Forward or Rewind.
2) At Fast Forward,“BRbaeis turned ON and the take-
1-3. FAST FORWARD AND REWIND SPEED
CONTROL CIRCUIT
1) The, reel motors employed in this deck are
DC motors which at a non-load condition rotates
at about 3,000 rpm. Consequently, when Fast
Foward or Rewind is effected, there is a possibility
of tape damage due to a gradual build-up of inertia
and increased revolutions. This circuit is for the
purpose of controlling supply voltage to the take-
up reel motor for suppression of increased motor
revolutions.
2) When the deck is set to Fast Forward mode, TR1I2.
is turned ON and the take-up motor begins to
rotate. When the supply reel motor is not rotating,
because bias is not supplied to the base of TR3,
the resistance between TR3 collector and emitter
is infinite, and a fixed bias is supplied to TR4
through R8 and R9, a fixed DC voltage is supplied
to the take-up reel motor, and there is a build-up
of inertia and gradual increase in motor revolu-_
tions. F
However, at Fast Forward Mode, the supply reel
motor of this deck functions as a generator.
Consequently, the electromotive force generated
by the supply reel motor passes D6, D85, R6 and
R119 and becomes TR3 base bias, and the
resistance between TR3 collector and emitter is
varied proportionately according to the extent of
the generator’s electromotive force.
That is to say, R9 and the resistance between TR3
collector and emitter becomes parallel composite
resistance and bias to TR4 is varied by this com-
posite resistance. Momentarily, when the take-up
reel motor begins to rotate at high speed, this
counterbalanced electromotive force is generated
by the supply reel motor and this generated
voltage increases the resistance between TR4
collector and emitter and the supply voltage to the
take-up reel motor is decreased. Thus, motor
revolutions are slowed for a decrease in speed.
In this manner, the take-up speed always corre-
sponds with the supply reel motor speed, thus
avoiding high speed motor revolutions.
3) Speed control also functions in exactly the same
way at Rewind mode. However, in this case, the
right hand side reel motor functions as a generator,
and left hand side reel motor revolutions are
controlled by means of supply voltage control.
Therefore, Rewind speed is controlled in the same
way as at Fast Forward.
1-4. MAGNETIC BRAKING CIRCUIT
1) This deck differs from other 3 motor system decks
to date in that instead of a mechanical braking
system, tape travel is stopped electrically, and a
magnetic braking system is employed. When Fast -”
Forward or Rewind is being effected, the take-up
motor rotates while being controlled by the
rotation of the supply side motor. ;
This circuit is for the purpose of applying mag-
up motor rotates. The supply side motor rotates
and functions as a generator to maintain proper
take-up motor revolutions. At this time, the
magnetic braking circuit maintains TR8 and TR10
at ON, and TR9 and TRi!I at OFF condition.
D12 is grounded through D13 and D12 anode
becomes identical to grounding electrical potential.
Consequently, TR7 assumes an OFF condition.
(In other words, current does not flow to the
supply side motor).
3) When the deck is stopped from Fast Forward
mode, TR12 is turned OFF, and the current to the
take-up motor ceases. Also TR14 is turned ON and
’ TR13 turned OFF, and at the same time, D1
anode assumes a floating condition. Current flows
by means of the electromotive force from the
take-up sige motor, and this current turns ON TR7
and voltage is supplied to the supply side motor.
This voltage becomes the braking voltage of the
supply side motor.
4) When magnetic braking is first applied, because the
take-up motor is rotating fairly fast, a large
electromotive force is generated, TR17 is turned
completely ON, and maximum voltage is supplied
to the supply side motor. Thus, speed is reduced
and at the same time, this voltage is decreased.
Also the take-up motor electromotive foree~~
disappears, and at the same time, the supply side
motor rotation stops. :
5) When the deck is stopped from Fast Forward
mode, the operation is the same as described
above. Only the circuit components differ..
1-5. AUTOMATIC SHUT-OFF MECHANISM CIRCUIT
1) This circuit is for the purpose of effecting auto-
matic shut-off when tape travel has stopped after
play, recording, fast forward, or rewind mode.
2) During tape travel, because the rotary magnet
. rotates, Stop Detection circuit TR1 performs the
ON + OFF switching operation. Also during tape
travel, because D30 anode becomes grounding
electrical potential, TRI7 is turned OFF.
However, charge and discharge current alternately
flows to C9 by means of the Stop Detection
circuit. At charging time, current flows to
R55 > C9 + D31 + C10, and TR17 is turned ON.
At discharging time, current flows to R56 > D27
+ C9 > TRI (stop detection circuit). During this
time, C10 discharge current passes R58 and TR17
is maintained at ON condition. When tape travel
has stopped, C9 charge and discharge current will
not flow, C10 discharge current also ends, and
TR17 is turned OFF. Then TR18 is turned ON,
and the diode connected to TR18 collector for
instance, if automatic shut off is effected from
play mode, D70 is grounded, play circuit TR32 is
turned OFF, and Shut-off mode is effected.
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