Akai GX-747 dbx Service Manual

SECTION 1
SERVICE MANUAL
TABLE OF CONTENTS
I. SPECIFICATIONS ......................................................... 4
II. DISMANTLING OF UNIT .................................................... 5
III. CONTROLS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
N. PRJNCIPALPARTSLOCATION ............................................... 7
V. VOLTAGE AND CYCLE CONVERSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1. VOLTAGE CONVERSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
2. CYCLE CONVERSION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
VI. DESCRIPTION OF CIRCUIT OPERATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
1. OUTLINE ............................................................• 9
2. DETAILS AND FEATURES OF EE TAPE ....................................... 9
3. dbx NOISE REDUCTION SYSTEM ................................................... 11
4. EXPLANATION OF EACH OPERATING PRINCIPLES .............................. 12
VII. MECHANISM ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28
1. GUIDE ROLLER LOOSE PLAY ADJUSTMENT ................................... 28
2. MICRO SWITCH POSITION ADJUSTMENT ...................................... 28
3. REEL TABLE HEIGHT ADJUSTMENT ......................................... 29
4. CAPSTAN SHAFT LOOSE PLAY ADJUSTMENT .................................. 29
5. BRAKE BAND POSITION ADJUSTMENT AND BRAKE TENSION ADJUSTMENT ........... 29
6. PINCH ROLLER POSITION ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30
7. PAUSE PLUNGER POSITION ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • 30
8. PINCH ROLLER PRESSURE ADJUSTMENT ....................................• 30
9. CUE MICRO SWITCH POSITION ADJUSTMENT .......................................• 30
10. TAPE SPEED ADJUSTMENT ................................................ 31
VIII. HEAD ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
IX. ELECTRICAL ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34
1. CLOCK FREQUENCY ADJUSTMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . • 34
2. PHOTO TRANSISTOR SENSITIVITY .........................................• 34
3. PRE-AMPLIFIER P.C BOARD ADJUSTMENT. ......................................... 35
4, dbx NR P.C BOARD ADJUSTMENT ................................... , . . . . . . . . . . . . 39
X. DC RESISTANCE OF VARIOUS COILS .......................................... 41
XI. CLASSIFICATION OF VARIO USP .C BOARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
1. P.C BOARD TITLES AND IDENTIFICATION NUMBERS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42
2. COMPOSITION OF V ARlOUS P.C BOARDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43
For basic adjustments, measuring methods, and operating principles, refer to GENERAL TECHNICAL MANU.AL.
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3

Akai GX-747 dbx Specifications

General

Track System	4-track, 2-channel stereo
Reel Size	up to 10.5 inch reel
Type	Reel to Reel
Heads	2 x erase
Motor	1 x capstan, 2 x reel
Tape Speed	9.5 cm/s, 19 cm/s
Wow and Flutter	0.03% (19 cm/s)
Signal to Noise Ratio	65dB
Input	1 x line, 1 x microphone
Output	1 x line
Dimensions	440 x 480 x 260 mm