Akai GX 77 Service Manual 1

Page 1

Olf’fl/ \

STEREO TAPE DECK

MODEL GX- 7 7

THIS MANUAL IS ALSO APPLICABLE TO BOTH SILVER

AND BLACK PANEL MODELS
SECTION I SERVICE MANUAL .................... 3
SECTION 2 PARTS LIST .......................... 45

SECTION 3 SCHEMATIC DIAGRAM ................ 65

Page 2

SAFETY INSTRUCTIONS

SAFETY CHECK AFTER SERVICING

Confirm the specified insulation resistance between power cord plug prongs and externally exposed parts ofthe set is
greater than 10 Mohms, but for equipment with external antenna terminals (tuner, receiver, etc.) and is intended for
or I, specified insulation resistance should be more than 2.2 Mohms (ground terminals, microphone jacks.
headphone jacks. line-in-out jacks etc.)

PRECAUTIONS DURING SERVICING

l.

owso

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

D D

Observe that wires do not contact heat producing parts (heatsinks. oxide metal film resistors, fusible resistors. etclr
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.

Page 23

LINKED WITH COUNTER

LAMP PCB

£22 DETECTION ROLLER

DETECTION
HOLDER

DETECTION PCB

TR2 (PHOTO TRANSISTOR) TRI (PHOTO TRANSISTOR)

‘ 4. '2.5
.e Smsec—aem sec—)I

TR2
TAPE PULSE

u d)
ROLLER @

IC—I

(UP/DOWN)

lC—I

(TAPE PULSE) '

W

lC-I

__F

m-.. __|

3) COUNTER Operation (Refer to Figs. 25, 26)

The output of TRl is inputted into ICl D12 ®>
after waveform shaping in the Schmitt Circuit of
TR18 and TRI9. The output of TR2 is inputted
into [Cl (33) after waveform shaping in TRIS to
TR17, and depending on the phase relation, it
conducts UP or DOWN count. (For the waveform
of TRIS-l7, see auto-stop circuit).

Input waveforms of [Cl (ID, (ID (Counter Circuit)

Fig. 25

FF MODE
(TYPICAL)

UP COUNT

RWD
(TYPICAL)

00w N cou NT

Fig. 26

23