Akai GX-77 User manual

STEREO TAPE DECK
eens X= i Ai
THIS MANUAL IS ALSO APPLICABLE TO BOTH SILVER
AND BLACK PANEL MODELS
SECTION 1 SERVICE MANUAL .................-4- 3
SECTION 2 PARTS LIST 32... csc ce ca eewen ved 45
SECTION 3 SCHEMATIC DIAGRAM ................ 65

SAFETY INSTRUCTIONS
SAFETY CHECK AFTER SERVICING
Confirm
the
specified
insulation
resistance
between
power
cord
plug
prongs
and
externally
exposed
parts
of
the
set
is
greater
than
10
Mohms,
but
for
equipment
with
external
antenna
terminals
(tuner,
receiver,
etc.)
and
is
intended
for
or
[A],
specified
insulation
resistance
should
be
more
than
2.2
Mohms
(ground
terminals,
microphone
jacks,
headphone
jacks.
line-in-out
jacks
etc.)
PRECAUTIONS DURING SERVICING
1.
0 | ID
Parts
identified
by
the
A\
symbol
parts
are
critical
for
safety.
Replace only with parts number specified.
In
addition
to
safety,
other
parts
and
assemblies
are
specified
for
conformance
with
such
regulations
as
those
applying
to
spurious
radiation.
These
must
also
be
replaced
only
with
specified
replacements.
Examples: RF converters, tuner units, antenna selector switches, RF cables, noise blocking capacitors, noise
blocking filters, etc.
Use specified internal wiring. Note especially:
1) Wires covered with PVC tubing
2) Double insulated wires
3) High voltage leads
Use specified insulating materials for hazardous live parts. Note especially:
1) Insulation Tape
2) PVC tubing
3) Spacers (Insulating Barriers)
4) Insulation sheets for transistors
When replacing AC primary side components (transformers, power cords, noise blocking capacitors, etc.), wrap
ends of wires securely about the terminals before soldering.
c> c>
Observe that wires do not contact heat producing parts (heatsinks, oxide metal film resistors, fusible resistors, etc.).
Check that replaced wires do not contact sharp edged or pointed parts.
Also check areas surrounding repaired locations.
Use care that foreign objects (screws, solder droplets, etc.) do not remain inside the set.

I. SPECIFICATIONS
TRACK SYSTEM
REEL CAPACITY
HEADS
MOTORS
TAPE SPEED
WOW & FLUTTER
TAPE WINDING TIME
FREQUENCY RESPONSE (Using a EE Tape)
SIGNAL TO NOISE RATIO
HARMONIC DISTORTION
INPUT
OUTPUT
DIN
DIMENSIONS
WEIGHT
POWER REQUIREMENTS
POWER CONSUMPTION
4 Track 2 Channel Stereo System
Up to 7” reel
GX head for Recording x 2
GX head for Playback x 2
Erase head x 2
FG Servo DC motor for capstan drive x 1
DC motor for reel drive x 2
19 cm/s + 0.8% (7-1/2 ips.)
9.5 cm/s + 1.0% (3-3/4 ips.)
Less than 0.03% WRMS, 0.07% DIN 45500 at 19 cm/s
Less than 0.04% WRMS, 0.10% DIN 45500 at 9.5 cm/s
80 sec. using 360 m (1200 ft.) tape
25 to 33,000 Hz + 3 dB (-20 VU) at 19 cm/s
25 to 26,000 Hz + 3 dB (0 VU) at 19 cm/s
25 to 25,000 Hz + 3 dB (-20 VU) at 9.5 cm/s
25 to 15,000 Hz + 3 dB (0 VU) at 9.5 cm/s
Better than 63 dB at 19 cm/s DIN 45500
Less than 0.5% at 19 cm/s
Required microphone impedance: 600 ohms
Line: 70 mV (input impedance 47 kohms)
Line: 0.775V at 0 VU
Required load impedance: more than 20 kohms
Phone: 1.3 mV/8 ohms at 0 VU
Input: 2.0 mV (input impedance 10 kohms)
Output: 0.3V
Required load impedance: more than 20 kohms
440(W) x 244(H) x 227(D) mm
(17.3 x 9.6 x 8.9’)
17.0 kg (37.5 Ibs)
100V, 50/60 Hz for Japan
120V, 60 Hz for USA and Canada
220V, 50 Hz for Europe except UK
240V, 50 Hz for UK and Australia
110/120/220/240V, 50/60 Hz switchable for the other countries
JPN 30W U/T, CSA, AAL SOW
* For improvement purposes, specifications and design are subject to change without notice.

SECTION 1
SERVICE MANUAL
TABLE OF CONTENTS
SPECIFICATIONS 5.3 f0:3h 0 site ives fota no AM EA, ei teca a Na Se sei
DISMANTLING OF UNIT... 2.0.0.0... ee ee ee ens
CONTROLS © i532, 505 tiny eSieeals BS eters era BALE Gene ote Ges BE a
PRINCIPAL PARTS LOCATION ............ 0... 0c cee ee eee eee
VOLTAGE AND CYCLE CONVERSION. ............. 0.000220 ee
1. VOLTAGE CONVERSION ........... 0.0.0 cece eee eee
2. CYCLE CONVERSION }j oo sscis a ceed i ee wens Me Ewe ae
VI. OPERATING PRINCIPLES ............ 2.0.0 cece eee eee
1. TIMING CHART OF EACH MODE ............. 2.200000 e eens
2. EXPLANATION OF EACH MODE............... 000000 e ee eee
3. EXPLANATION OF EACH CIRCUIT ................0 0.00005,
VII. MECHANISM ADJUSTMENT ......... 0.00. ccc cece ee eee eee
1. BRAKE BAND POSITION ADJUSTMENT AND
BRAKE TENSION ADJUSTMENT ...........
2. PLAY PLUNGER POSITION ADJUSTMENT .................45.
3. PINCH ROLLER PRESSURE ADJUSTMENT ...............--..
4. TENSION SERVO ADJUSTMENT ............ 0... eee eens
5
6
<295>
. LOADER PLUNGER POSITION ADJUSTMENT .................
. TAPE SPEED ADJUSTMENT .... 2... 0... cece ees
. HEAD ADJUSTMENT ... 10... 0... cc ec ee eens
AMPLIFIER ADJUSTMENT .... 2.0.2... cc ccc ee eens
DC RESISTANCE OF VARIOUS COILS ........... 0.0.2. ee eens
CLASSIFICATION OF VARIOUS P.C BOARDS ................06.
1. P.C BOARD TITLES AND IDENTIFICATION NUMBERS...........
2. COMPOSITION OF VARIOUS P.C BOARDS ............-....---
HeR
For basic adjustments, measuring methods, and operating principles, refer to GENERAL TECHNICAL
MANUAL.

SCREWS
lil. CONTROLS
OS eS re
=~SOONDAHRWON>OO
DSS OVE AN
POWER SWITCH
SUPPLY REEL TABLE
REEL STOPPER
TENSION ARM
CAPSTAN
HEAD COVER
REAL TIME COUNTER and RESET BUTTON
PINCH ROLLER
TENSION ARM
REEL STOPPER
. TAKE UP REEL TABLE
. TIMER START SELECTOR
REVERSE (REV) SELECTOR
. HEADPHONE (PHONES) JACK
OUTPUT CONTROL
RECORDING INPUT CONTROLS (REC-L, REC-R)
. MONITOR SELECTOR
BIAS ADJUSTMENT (ADJUST) CONTROL
RECORDING (REC) MASTER CONTROL
- TAPE SELECTOR
. TAPE SPEED SELECTOR
22.
23.
24.
25.
26.
27.
28.
29.
30.
31.
32.
33.
DIGITAL BAR METERS
CUE/REVIEW LEVER
LOADING ROLLER UP/DOWN BUTTON
OPERATION BUTTONS
RECORDING BUTTON (@ REC) and INDICATOR
PAUSE BUTTON ( 88) and INDICATOR
REVERSE BUTTON { « }
FORWARD BUTTON ( » }
REWIND BUTTON ( ~e<« )
STOP BUTTON ( @ )
FAST FORWARD BUTTON ( = )
STANDBY/DIRECTION INDICATORS ( <¢ and »)
REMOTE CONTROL JACK
EXTERNAL POWER SUPPLY JACK
(INPUT DC 15V 200 mA)
POWER CORD
LINE IN JACKS
LINE OUT JACKS
LOADING ROLLER
SENSING PINS
DIN JACK (Some models do not have this facility}

i.
DISMANTLING
OF
UNIT
In
case
of
trouble,
etc.
necessitating
dismantling,
please
dismantle
in
the
order
shown
in
the
photographs.
Reassemble
in
reverse
order.
SCREWS
SCREWS
anos
=e Gl eee
SCREWS
SCREWS
GEE)
2
BOTTOM
COVER
SCREWS
SCREWS
SCREWS
BACK BOARD SCREWS

IV.
PRINCIPAL
PARTS
LOCATION
HEAD
BLOCK(REV)
HEAD
BLOCK(FWD)
TENSION
COUNTER
PCB
LOADER
SWITCH
TENSION
ARMI(L)
TIO1005220
Sw305
ARMIR)
REC R
INPUT CONTROLS ,
POWER Swi TCH—> |
PHONES 4 :
OUTPUT LEVEL CONTROL
MONITOR SWITCH
BIAS ADJUSTMENT CONTROL
REC MASTER CONTROL
LOADING
ROLLER
OPERATION
BLOCK
LOADING ROLLER
UP/DOWN BUTTON
CUE/REVIEW LEVER
TAPE SPEED SWITCH
TAPE SELECTOR
Fig.2 Front View
i
}
be
|
REMOCON JACK AC ADAPTER JACK
Ji J9OI
Fig.3 Rear View

Fig. 1 Controls
TA
AT
MN
IN
A
PANY
ON
I
ease
soe
win

VI. OPERATING: PRINCIPLES
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Fig.5 Syscon Block Diagram
10

V. VOLTAGE AND CYCLE CONVERSION
POWER TRANS TSO!
VOLTAGE SELECTOR VS |
@|
a
AC CORD
Fig.4 Voltage Conversion (U/T Model Only)
. VOLTAGE CONVERSION
Models for Canada, Europe, USA, UK, Australia and
Japan are not equipped with this facility.
Each machine is preset at the factory according to
destination, but some machines can be set to 110V,
120V or 240V as required.
If voltage change is necessary, this can be accom-
plished as follows:
1) Remove the back board and look for the voltage
selector on the center portion of the machine.
2) Change the position of voltage selector plugs so
that
the
voltage
to
be
used
coincides
with
the
voltage
shown
through
the
opening
of
voltage
selector
plug.
oe
rm
. CYCLE CONVERSION
With
DC
motor,
cycle
conversion
is
not
necessary.
A
ence,
“oO