Akai GX-635D User manual

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STEREO TAPE DECI(
Mo,)',,
GX'635D
SECTION
1 SERVICE
MANUAL. I
SECTION2
PARTSLIST.. ........43
SECTION3
SCHEMATIC
DIAGRAM ......67

I. TECHNICAL DATA
TRACK
SYSTEM
REELCAPACITY
TAPESPEED
WOW
& FLUTTER
FREQUENCY
RESPONSE
DISTORTION
(1.000
Hz
"0" VU)
SIGNAL
TO NOISE
RATIO
ERASE
RATIO
CROSS
TALK
CHANNEL
SEPARATION
BIAS
FREQUENCY
HEADS
MOTORS
REALTIMECOUNTER
FF & RWD
TIME
OUTPUT
JACKS
INPUTJACKS
DIN JACK
DIMENSIONS
WEIGHT
POWER
REQUIREMENT
* Specificationsdetermined with Akai LN-150-7 or SCOTCH #21
* For improvement'purposes' specifications
and design
aresubject
4 lrack 2 channel stereo/monaural system
Up
to 10-l/2"
reel
19cm/s
x0.8%
(7
-l12
ips)
9.5
cm/s
xl.0%
(3-314
ips)
(Pitch
control: more
lhan
t6%)
Less
than0.03%
WRMSat 19cm/s
Less
than
0.04%
WRMSat9.5
cm/s
Less
than
0.08%
DIN
45500
at 19
cm/s
Less
than0.10%
DIN45500
at9.5cm/s
30
to 27,000
Hz
13
dBat19
cm/susing
WR
Tape
30to 21,000Hz
13
dBat9.5
cm/s
using
WRTape
30
to 25,000
Hz
t3 dBat19 cm/susing
LNTape
30
to 19.000
Hz 13dB at9.5cm/susing
LN Tape
Less
than 05% aI 19 cmls
Better
than62
dBDIN45500
Better
than70dB
(at
1,000Hz)
Betterthan
40
dB
(at
1,000
Hz)
Better
than55dB
(at
1,000
Hz)
100
kHz
(6): Two GX Recording Heads, Two GX Playback Heads,Two Erase
Heads
(3): One
ACServoMotorfor capstan
Drive
TwoACEddy
currentMotors
for Reel
Drive
Up
to 99
min59sec,
Less
than
r1.5%
120
sec
using550m
(1,800
ft.)TaPe
Line
(2): 0.775V
(0
VU)
Required
loadimpedance:
more
than
20kohms
Phone
(1): 100
mV/8ohms
Microphone
(2): 0.25
mV
Requiredmicrophone
impedance:
600ohms
LINE
(2): 70mVimpedance
100
kohms
Input2.0mV,
impedance
l0 kohms,
Ot 0.3V
440(W)
x483(H)
x 256(D)
mm, (17.4
x 19'0
x 10.1")
2l ke(46.4
lbs)
100V.50/60
HzforJPN
120V,60
Hz
forUS
& Canada
2201240V,50
Hz for Europe,UK and
Australia
1lO
|120 |220 I
240V,5 0/60Hzinternally
switchable
for other
countries
1tape unless
otherwise noted.
to change
without notice.
4

II. DISMANTLING OF UNIT
In case of trouble,etc.necessitating
dismantling,
please
dismantle
in theordershownin thephotographs.
Reassemble
in reverse
order.
6
SCREWSA ffML KrcBS

)

III. CONTROLS
1. PITCH
CONTROL
2. SUPPLYREELTABLE
3. BUILT-IN
REELRETAINER
(Left}
4. LEFT
TENSIONARM
5. PINCH
ROLLER
6. RECORDINGMUTE
SWITCH
(REC
MUTE)/TIMING
LAMP
7, REEL
SIZESELECTOR
8. REVERSE
SELECTOR
9. POWER
SWITCH
10. VUMETER
(Right)
11. VUMETER
(Left}
12. TAPESELECTOR
13, TAPE
SPEED
SELECTOR
14. TIMER
START
15. HEADPHONE
JACK
16. OUTPUT
LEVELCONTROL
Fig.I Controls
17. MONITORSWITCH
18. REAL TIME COUNTER and RESET
BUTTON
19. TAKE-UP REELTABLE
20. BUILT-lNREELRETAINER
(Risht)
21. RIGHTTENSIONARM
22. HEAD COVER
23. RECORDING
INDICATORLAMP
24. PAUSEINDICATOR LAMP
25. REVERSEDIBECTION/STAND
BY INDICATOR LAMP
26. FORWARD DIRECTION/STAND
BY INDICATOR LAMP
27. MODE BUTTONS
28. MICROPHONEINPUT CONTROLS
29. MEMORYMARKERS
30. LINE INPUTCONTROLS
31. MICROPHONEJACKS (Left/Right)
32. RECORDING
MODE
SWITCH

IV. PRINCIPAL PARTS LOCATION
BRAKE
MICRO
SWITCH
sw906
BRAKE
PLUNGERSL9O3
RNCHROLLER
PLUNGERSL9O2
PAJSE
PLUNGERSL9O4
PIÍCH CONTROL
VOLUME
VR9OI
REAL
TIME
COUNÍER
TENSION
ARM
(R)
HEAD
BLOCK
PHONESJACK
OIJTPUTLEVELCONTROL
VOLUME
LR
RECMOOESWITCH
TAPESELECTORSWITCH
OPERATIONELOCK
REC
MODE
INOICATOR
MIC
rl- RÊcLEVEL
rrrup
J VOLUME
Fig.2 Front View
MONITORSWITCH TAPESPEEDSWITCH
J
TENSION
ARM(L}
RECMUTESWITCH
SW9O4
REELSIZE S1,VITCHSW9O3
REVERSESELECTORSWITCH
POWERSWTTCHSW90l
",n,.** {.
IIMERSTARTSWITCH

REMO,CONJACKJ9O5 VOLTAGE
SELECTOR
REELMOTOR RIGHT
M902 24XO-TD FUSE
PC BOARD
TH-20rro
SYS.CON PC BOARD
TH-rOr5
CAPSTANMOTOR
M903 SCM-200
PRE AMPPC BOARD
TH-500r4
Fie.
3 RearView
OPERATION
P,CBOARO
TH-2041
OPERATIONP.C
BOARO
ÍH-2042
VOLUMEPC BGRD
TH-5002

V. CIRCUIT OPERATING PRINCIPLES
1.SYSTEM
CONTROLOPERATION
SYMBOL TRUTH
TABLE
NOT
CIRCUIT
X=A
F-tfit
loll
rl
I'IFI
NAND
CIRCUIT
X=AE
NOR
CIRCUIT
X=A+B
J
O=
LOW
LEVEL
I: HIGHLEVEL
Chart-1
J
10

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r'_f
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Schematic-lSTOP
MODE
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Schematic-2
FWD-PLAYMODE

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Schematic-4FWD-RECMODE

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Schematic-5REV-REC
MODE
15

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ar-) {'ll I
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Schematic-6
FF MODE
I6

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taÊ
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Schematic-7RWDMODE
17

I-I. CIRCUIT CONSTRUCTION
OF ICI M544IOP
Thedesign
oi M54410P
until now
tradSTOP,
pt-nY.
REC,
FF, RWD,
PAUSEand
REC
preventing
AR as
its input terminals.GX-635D circuit is constructed
with FWD in place
of PAUSEandREV in place
of
PLAY. Pauseis controlled by a flip flop with a
separate
IC.
l) Block Diagram
ST
T
I
I
)
I
--'l
4.,
\)7 '--
I
I
IFAST
FF
Fig.4 M544l0P
/. 1
I
@
l8

Terminal
Name Terminal
Function
Operation
input
terminals
STOP lnputterminal
forstopping
operation
FF Inputterminal
for fast
forward
RWD Input terminal
for rewind
FWD Input
terminal
forplaybackinthe
forwarddirection
REV Inputterminal
forplaybackinthereverse
direction
REC- Input
terminalforrecording
Controlinput terminalAR Inputterminal
for preventingrecording
Output
terminals
FAST Terminal
with "H" signal
output
during
fast
forwardorrewind
mode
FF Terminal
with "H" signal
outputduring
fastforwardmode
F}VD Terminal
with "H" signal output during
forward
playback
mode
REV Terminal
with "H" signal
output
during
reverse
playbackmode
REC Terminal
with "H" signal
output
during
recording
orREC/Pausemode
2) Terminals
andtheir functions
3) Operation
activated
by each
input
NOTES: 1. The
input signal
isactivated
by thefall of _]-f .
2. The
outputismaintained
until thenextinput signal.
3. AR isacontrolinput terminal
and
theREC
output isnot "H" when
AR
4. When
AR = "L" signal
issupplied
during
the
RECoutput
is
"H", REC
output
becomes
"L".
5. At the
moment
the
power
ison,
alloutput
will be
"L" and
theStop
mode
will be
effected.
4) Regarding
the input circuit'sdiode
Dl3
Previously
M54410P
has
beenso
designed
that
the
first terminal was FLAY input and the sixth
terminal was PAUSE input. But in GX-635D,
pLly is used for REV and PAUSE for FWD.
Consequently,
gÍounding only the 6th terminal
(FWD) will not allow the modes
to be changed
Chart-2
Chart-3
directly from FF or RWD to FWD. For this
reason,
the firstterminal
(ngVt isalso
grounded
through diode Dl3 releasing
FF and RWD. In
addition,
even
if there
aresimultaneous
inputs
into
both F\tD and REV, FWD mode output is
designed
to take
prioritY.
lnpul Signal Output Output
Mode
FAST FF FWD REV REC
STOF LLLLLSTOP
Mode
FF HHLLLFF Mode
RWD HLLLLRWDMode
FWD LLHLLFWD
Mode
REV LLLHLREV Mode
REC/FWD LLHLHREC/FWD
Mode
REE/REV LLLHHREC/REV
Mode
t9

VELOCITY
+ PULSEWIDTH CONVERSION
r\
501
@
I-2. CIRCUIT FOR PREVENTING CLICK NOISE
DURING TIMER RECORDING
l) When
thepower isturned
on for timer
recording,
recording must take place after the amplifier
circuitisin full operation
or else clicknoise
will be
recorded.Alsowhen
thepower
isturnedoff, Rec
Final Mute must operatebefore the amplifier
circuit ceasesto operate
oÍ elseclick noise
will be
recorded.This circuit prevents
such click noise
frombeingrecorded.
2) In ordinary recording,base
electric
cuÍrentflows
to TR28 basethrough
R89and
R90,andTR28
is
ON. Therefore,
Rec Final Mute relay RLI @re
Amp P.CBoard)connected
to TR28 collector
is
operatingto supply the signals
to the recording
headand
therecordingmode
iseffected.
3) When the power is turnedON at timer recording
stand-by,
baseelectriccurrent
issupplied
toTR27
base
only while C42 isbeingcharged
and
TR27is
turned ON. When
TR27 is turned ON, electric
potentialisnot supplied
to TR28base
andTR28
is turned off. Consequently
relay RLI does
not
operate
andRechead
isnot supplied
with asignal.
SinceTR27 turns off onceC42 is charged,
base
electriccurrent flows to TR28 base
throughR89
and
R90.
Because
relay RLI function only after the ampli-
fiercircuit isin complete
operation,
theclicknoise
is
avoided.
4) TR20 and TR2l is OFF during
recordingmode
and
for thisreasonC32andC33are
charged.
Whenthe poweristurnedoff in thiscondition,
by
the chargingvoltage on C33 TR20 base will
becomelowerthantheemitterin electric
potential
and
turnsON.TR2l isalso
suppliedwith electric
currentthereby
andis turned
on. When
TR21is
turned on,C32 isdischarged,and
ICI terminal2
(Stop-) becomes ground potential through D24.
This releases
the deck from the recording
mode
and
thestopmode
iseffected.
This operation takes placebefore the amplifier
circuit stopsand thereforethe click noiseis cut
out.
Fig.5 Block
Diagram
2.THF.SAMPLE
AND HOLD SYSTEM
SERVO
MOTOR
(SCM-200)
OPERATION
l) Servo
signals
generallycreated
proportionatelyto
the number
of revolutions
of themotor are
shown
either as frequency deviations
or voltage
deflec-
tions. The motor employed in GX-635D uses
frequencydeviation
unaffected
by time constants,
etc., of the load circuit as input signal
to the
motor drive circuit through pulse
width conver-
sion.
This pulse width variesproportionately to the
deviations
in the number
of motor rotations.
The
deviation
is detected,
converted
to avoltage
value,
is held at that voltage
until the next servo
signal
pulse,and then impressed
into the motor drive
circuit.
Meanwhile,
since
it requires
aholdingcircuit and
because112 pulse
are
generatedfor each
motor
rotation, time constants
of circuits
coming
before
the Sample and Hold circuit can be greatly
reduced compared to the conventional
voltage
deflection
detection
system.
For the reasonsabove,
it features
quick response
to motor revolutions,
minimum influence
by tem-
perature,
andfewerchances
of faulty mechanism.
In addition, due to the inclusion of the servo
voltage
holdingcircuit, ripple content
of theservo
voltageholdingcircuit, ripplecontentof theservo
voltagehas been sharply reduced
to result in a
smooth
andstable
tape
transport
with aminimum
ofwow
& flutter.
L|l
20

3-3/4+7-l/2
lprrrclrJoNrRoll
FÀPSTAN
MoToE
Fig.6
FG INPUT SIGNAL O
__L
THRESHOLD
LEVEL
(d)
TR8 BASE
(e)TRB COLLECTOR
1_i* i'
^l t
uJ-
(Í) TR9 COLLECTOR
(9) rRlO
(h)
TRrl
(r)TRl2
BASE
É
ÍsERVo
ourPUn
TR12 CtA
t/tOO
lx
t- ó
9;
*l r.
IIt(
lo
t:
lrRro *
/á
=[
tn T_
I
-O-
AADE
qE
ry L
D9
---1
r. I
TR4
R4 220
t5 2,?K
e
I
9l !
croooilí
.-r--
:+
_2
.E
\:
TR5
=lÈ
Ia8.
\ ",
3:
(TR7
i
(;
q
IR€
ró
3
I
I
:
E
Kin
L__
TR13
trt
__J
Át
Í
-'_.\
ÍR6 9
\j x
rK8
2l
Fis.7
(j) TR12
COLLECTOR

2) Explanation of the circuit operation
(Refer
to
Figs.
6,7)
The velocity signalobtained
from the motor's
frequency
generator
isshapedinto awaveformin
theperiod of "T" proportionate tothevelocityas
in (a) on collector TR6. This signalis differen-
tiated and entersTR7 base.This makesTR7's
collectoroutput as in (c) and turns ON TRl0
duringthetimeof thenegative
pulse.
MeanwhileTR8 baseis suppliedwith awaveform
like (d) andwhenit reachesthe threshold
level,
TR8 is turned on. A waveform (e) with pulse
width "11
" isobtained
from thecollector.During
thetime "T" that TR28isON,TR9 baseelectric
potential
decreasesto turnON.
Consequently,TRI I base electric potential
inèreases
and
TRI I isalso turned
ONforthe time
"tr".
When the period "T" varies
with the velocity,
the pulse
width "t1
" variesaccording
to TRS's
threshold
level.
But whenTRl0 is on, it is con-
stantdue to the time constant.
So
that by using
the period that TR is ON as the standard
pulse,
the pulse
width "t2
" isconstant
regardless
of the
velocity.
(g) and(h) show
the ON andOFF conditionof
TRl0 and TRll. Whenthe electric
charge
that
waschargedto C16 isdischargedduring thetime
TRl I isON"t1", asignalvoltageof "e" propor-
tionate
to thevelocitycanbeobtained. Next,
with
"e" asitsbasis,Cl6 ischarged
during
thelimited
timeof thestandard
pulse
width"t, ", andby the
chargingvoltage"e" the charging is stopped.
The voltageis then held until the hext standard
pulse.
This
voltage
"e" issupplied
to theTRl2 baseand
a servosignal"E" is obtained.This servo
signal
"E" controls
TR13anddrivesthemotor.
As shown above,
since
"tt " and "t2" aresmall,
servo signalripples are made small and a near
direct
currentservosignal
is
obtained.
Inaddition,
the time constantsof the smoothingcircuit can
also be madesmallthat phase
lag factor can be
minimized.
22