Akai 280 DSS Service Manual

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TABLE OF CONTENTS

SPECIFICATIONS ..........................
MEASURING METHOD .....................
DISMANTLING OF TAPE TRANSPORT UNIT &

AMPLIFIERS .............................
MECHANISM ADJUSTMENT ..................
AMPLIFIER ADJUSTMENT ...................
TROUBLE SHOOTING CHART ................

. COMPOSITE VIEWS OF COMPONENTS ..........

SCHEMATIC DIAGRAM

WHEN PLACING ORDER FOR PARTS,
PLEASE USE SEPARATE PARTS LIST

2
4

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4. FROM STOP T0 FORWARD PLAYBACK
(RECORDING) (See Figs. 1, 2, and 3).

When the FWD Button is depressed, TR-107 emitter is
grounded, and TR-107 passes R-104 and is turned on.
TR-107 is maintained at on" by RL-104 contact point
Play-l.

The Pinch Roller Plunger and Brake Plunger current
passes Play-3 and is turned on. The voltage passes Play 4
and is divided by means of RIA (350 Q) and RZA
(50 8'2). About 55 V is supplied to the Take-Up Motor
and about 30V to the Supply Motor. At 7-1/2ips,
110 V is applied to the Main Motor and at 3-3/4 ips.
85 V is applied to the Main Motor.

At Forward Playback, TR-llO is turned on, and TR-l 11
is turned off. C-101 of TD. Circuit passes R-101 and is
charged.

5. 2-CHANNEL AUTOMATIC REVERSE
PLAYBACK (See Figs. 1, 2 and 4)

a) From Forward to Reverse Playback.

When the Reverse Button is depressed or when the
sensing tape passes the sensing pole, TR-l 10 is
turned off and TR-l 11 is turned on. Consequently,
RL-105, RL-106, and RL-l of Switch Board is
turned on. When RL-106 is momentarily turned on,
C-lOl passes R-103 and VR<101 and discharge
begins. C-lOl discharge current flows to the base of
TR-lOl and TR-102 and they are turned on. When
this occurs, RL-lOl is turned on, and Brake Plunger
as well as Pinch RollervPlunger is turned off. At this
time, the capstan motor begins reverse revolutions.
(While RL-lOl is on, because increased torque is
applied to the capstan motor, high voltage is
applied).

When discharge of C-lOl is completed,TR-101 and
TR-lOZ are turned off. RL-lOl is also turned off
and voltage is supplied to the Pinch Roller Plunger
as well as to the Brake Plunger and playback is
effected.

b) From Reverse to Forward Play

When the FWD Button is depressed or the sensing
tape passes the sensing pole, TR-lll is turned off,
and TR-llO is turned on. Because TR-lll is turned
off, RL-105 and RL-106 as well as RL-l are turned
off. When RL-106 is momentarily turned off,
CR-102 passes RL-103 and VR-lOl and discharge
commences. C-102 discharge current flows to the
base of TR-lOl and TR-102 and they are turned on.
When this occurs, RLrlOl is turned on and the
Brake Plunger as well as the Pinch Roller Plunger are
turned off. At this time, the capstan motor begins
forward revolutions. (While RL-lOl is on, be-
cause increased torque is applied to the capstan
motor, high voltage is applied).

When discharge of 0102 is completed, TR-lOl and
TR-102 is also turned off and voltage is supplied to
the Pinch Roller Plunger as well as to the Brake
Plunger and Forward Playback is effected. Charge of
C-IOl is begun. (If Shut<0ff Switch is at on
position, this operation will not take place).

6. FAST FORWARD (See Figs. 1 and 2)

When the Fast Forward Button is depressed, current
flows to RL-102 and RL-103. At the same time, TR-IOS
and FR-106 is maintained at on, and Fast Forward
operates. 100V is applied to the Take-Up Motor and
about 12 V to the Supply Motor.

When Fast Forward is effected from Forward Playback,
DR-113 is activated and cuts off TR~107.

When Fast Forward is effected from Reverse Playback,
D-l 14 is activated and cuts off TR-l 1 1.

When Fast Forward is effected from Rewind, TR-105
remains on, TR-106 operates and RL-103 is turned
on.

7. REWI'ND (See Figs. 1 and 2).

When the Rewind Button is depressed, TR-l 05 is
turned on. TR-lOS is maintained at on" by means of
RL-102. 100 V is applied to the Supply Motor and
about 12 V to the Take-Up Motor.

When Rewind is effected from Forward Playback,D-112
is activated and cuts off TR-107.

When Rewind is effected from Reverse Playback,D-108
is activated and cuts off TR-l 1 I.

When Rewind is effected from Fast Forward, D-104 is
activated and cuts off TR-106.

8. 4-CHANNEL REPEAT CIRCUIT
(See Figs. 5 and 6)

When the Stereo Selector is set to 4-Channel position,
Syscon Board- and. are opened. When {luring
Forward Playback, the sensing tape passes the reverse
sensing pole, TR-6 is turned off and TR-7 is turned on.
At this time, TR-4 is on" and TR-S is turned off.
Further, because TR-S is off and TR-9 on",[BEIis
grounded and at the same time, TR-107 is turned off.
TR-lOS is turned on and because it passes RL~102 is
held at on". Consequently, Rewind mode is attained
and the tape begins to rewind.

When the sensing tape passes the Forward sensing pole,
D1 is grounded, Tva is turned on, "FR-2 is turned off,
and TR-3 is turned on. Thus, TR-4 which has beenon up
to now is turned off and TR-S is turned from offlo on.
Because TR-S is on, the unit operates in the same was as
if the Forward Button had been depressed (TR-107 is
turned on, and TR-lOS is turned off. ConseqUently,

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Page 15

GEAR DETECTOR HEAD

SERVO COIL I

DISCRIMINATOR DC. AMP

AC AMP

91%

l'___"-__

DISCRIMINATOR OUTPUT

E2
El

E3
OUTPUT
fo f3 h f2
-> FREONENCY

Fig. 9

DC AMP. OUTPUT

E 3'
OUTPUT

Fig. 10

ADJUST so THAT m: 3mV t 0.5mv R.M.S. IS ATTAiNED AT 7 '/2 PS.
- MOTOR

Fig. 8 Servo Circuit Block Diagram

IN CASE 0 IS CHANGED (AT 7'/2 IPS)

f0 h" h H
-> FREONENCY
Fig, 11

IN CASE f0 IS CHANGED(AT 3374 IPS)

f0" fo {0' H'flh'
-> FREONENCY

Fig. l 2

l4