Akai GX 747 DBX Service Manual

Page 2

S'IER liU TA Pli DECK
HOMELG X-74-7d bX

SECTION 1 SERVICE MANUAL
SECTION 2 PARTS LIST $5

SECTION 3 SCHEMATIC DIAGRAM ................ 70

Page 7

CONTROLS

WflPSIRPN.

PNPPFPNTPW

BIJlLTrIN REEL RETAINER

SUPPLY REEL TABLE

MEMORY REVERSE INDICATOR
LEFT TENSION ARM (SENSING PIN)
PITCH CONTROL

REVERSE SELECTOR SWITCH
ELECTRONIC DIGITAL REAL TIME COUNTER
AUTO TIME COUNTER SYSTEM
PINCH ROLLER

POWER SWITCH

REEL SIZE SELECTOR
CUE/REVIEW LEVER

VU METERS

HEADPHONE JACK

OUTPUT LEVEL CONTROL

TIMER START SWITCH

MONITOR SELECTOR

TAPE SPEED SELECTOR

19.
20,
21.
22,
23
24,
25.
26.
27.
28
29.
3C.
31.
32.

34
35.
36.

Fig. 371 From View

Fig. 3-2 Rcux View

TAPE SELECTOR SWITCH
TRACK SELECTOR SWITCHES
BIAS ADJUSTMENT VOLUME
MICROPHONE JACKS

LINE INPUT CONTROLS
MICROPHONE INPUT CONTROLS
AUTO MUTE BUTTON
OPERATING BUTTONS

RIGHT TENSION ARM (SENSING PIN)
TAKE-UP REEL TABLE
BUILT~IN REEL TABLE

REMOTE CONTROL JACK

AC ADAPTER JACK

LINE IN JACKS

LINE OUT JACKS
POWER CORD
dbx NOISE REDUCTION SWITCH

SERVICE MANUAL GX-747dtn: W

Page 20

4-2-1 FUNCTION MODE SELECTOR CIRCUIT
Selection of the function mode is controlled
by the pulse timing using a microcomputer.
For easier understanding, one input terminal

will be explained as an example The
terminal@ receives four si- mals ilge
strobe signals from® tQW and2
Each pulse signal from® 28 and
. @has a different timing Assuming that the
signals from these terminals are 1000, 0100,
0010 and 0001, signal 1000 of Terminal
.will pass D84, and through the collector of
TR85, it will enter the emitter of TR60.
If FWD (SW3) button is pressed, the base of
TR60 is earthed through R202, TR60 is
energized, and Signal 1000 will be outputted
into Terminal @ of 1C1 through D60.

If any input is made into @ , it is processed
Within the microcomputer depending on the
signal and the signal is outputth from the
respective terminal. If 1000 is inputted into

@, it is judged as FWD and tile related

signal is inputted to the output terminal

(See Fig 6 27) Similarly, Signal 0100 from®
passes the emitter and collector of TR86 and
enters the Counter P.C Board. When the pro-
gram SW (SW6) is pressed, Signal 0100 is
inputted into 1C1 @. Signal 0010 from.pas-
ses the collector/emitter of TR87, and through
D66 and the reverse selector SW L ,it is
inputted into 1C1 @. Signal 0001 from a

. passes SR1 and SW906 and is inputted into

n
SELECTOR

Fig. 6-27
Input to @ Judgement and Output by Microcomputer
1000 Output H to Terminals @ ,®,. and @ of [C1 (FWD output order).
0100 Act as clear/program SW only when MEMORY AUTO REV SW is ON.
0010 Act once as a reverse equipment.
(SW 906 is ON and tension arm is locked)
0001 When FWD, REV, FF or RWD key is pressed, process the other signals after making
1 Terminal H.
Fig. 6-29 shows the truth table when the function switches are pressed. Fig' 6-28
Function SW l
Terminal FF FWD STOP REV REW PAUSE REC REC MUTE REC PAUSE
12 H H H H H H L H 1'1
13 L L L L L L H H H
L 14 H H L H H L H L L
15 H L H L H L L L L
16 L L L H L L L L L
17 L H L H L H H H II
24 H L L L H L L L L J
25 H H L H L L H H L j
Note: H of Terminal.: _1 Fig. 6-29

H of other Terminals: L-

SERVICE MANUAL GX-747dbx

l9

Page 35

IX. ELECTRICAL ADJ USTM ENT

34

_-W

SYSCON

A:B
|<-A+'B*|

Fig. 9-2

SERVICE MANUAL GX-74 7dhx

pPDS53C-l52

- CLOCK
Tpl l@|\ FREQUENCY

ICZ
yP0553C-HO

PCB TIOO9A2570

Fig. 9-1 Syscon P.C Board T1009A2570

1. CLOCK FREQUENCY ADJUSTMENT

(Refer to Fg. 9-1)
Connect the frequency counter between TPl (I C1 Pin
(D ) and GND, and adjust with IFTI so hat the
indicating values will be from 390 to 400 kHz
Also for the 1C2, make the same adjustment with
IFTZ.

. PHOTO TRANSISTOR SENSITIVITY

(Refer to Figs. 9-L , 9-2)
Connect the oscilloscope between TP3 and GND- For
the reel size 10, adjust with VR3 so that the ()N and
OFF widths of the pulse will be equal (AFB) as
shown in Fig 9-2 when the rotation is stabilized in
FF or REW mode.

Page 41

STEP 1333131413 INPUT SIGNAL TEST POINT AD £35111? RESULT REMARKS
Observe TP3 to TP6
TP-S (L) . .
VR2 SOkB
100 Hz TP-6 (R) m 3? °S°11l°s°°pe Refer to Fig.
(ENCODER) and adjust With VR2
RM.S -5 .5 dBm (ENCODER) 9-7.
2 and VR4 (50 KB) so
Symmetry (410 mV) from TP-3 (L) See Note 4.
, VR 450kB that the peak value of .
an oscrllator TP-4 (R) F lg. 9-8
(DEC ODER) (DECODER) the waveform becomes
constant at 200 Hz.
1000 Hz Each VRl 50 kB Adjust VRl (encoder)
ENCODER/ (ENCODER) and VR3 (decoder) so
V.C.A -5 .5 dBm . .
3 S t (410 V) from DECODER that the distortion at
ymme ry m 111 tor Output VR3 50 kB each terminal is mini-
c a Terminal (DECODER) mized (below 0.1%).
Adjust VRS (encoder)
H Each VRS 500 kB and VR6 (decoder) so
12050de ENCODER/ (ENCODER) that the output level of
4 ZERO ' m DECODER each output terminal
Pomt (410 mV) from
A Output corresponds to the in-
an oscfllator Terminal VR6 500 kB put at 75 5 dBm (410
(DECODER) mV). '
Make sure that during
encode and decode,
Confirmation 1000 Hz Each compression and ex~
of ENCODER ENCODER/ pansion are made in .
-5.5 dBm , . l Refer to Fig.
5 and +10 dB from DECODER Confirmation the proportion of 2 978
DECODER :m oscilla tor Output to 1, when the input '
Operation Terminal signal level is changed
by :10 dB. (See Fig.
9-8)
PEAK VALUE
I
I
l l
_ f. ____________ _ _
1 I
| I
' Sms I . _
'é-zoon 5 Fig. 9~7 Osc1lloscope Waveform
de NR ECB VtT,V.M OSCILLOSCOPE
m T E
to PG IN OUT m
o- -o
q é' o C 0
Fig. 9-8
INPUT LEVELS ENCODER OUTPUT LEVEL DECODER OUTPUT LEVEL
-15.5 dBm ~10.5 dBm -25.5 dBm
-5 .5 dBm -55 dBm -5.5 dBm
+4.5 dBm -0.5 dBm +14.5 dBm
* Tolerance of each output is :3 dB. 51$ 9.9

40

SERVICE MANUAL GX-747dbx

Page 56

SECTION 2

PARTS LIST

TABLE OF CONTENTS
RECOMMENDED SPARE PARTS ................................. 57
1. HEAD BLOCK ........................................ 58
2. MOTOR BLOCK ............................................ 59
3. REEL TABLE BLOCK ....................................... S9
4-. ROLLER TABLE (L/R) BLOCK ............................... 60
5. POWER BLOCK ............................................ 62
6. MECHA BLOCK ............................................ 63
7. SYS. CON P.C BOARD BLOCK ............................... 64
8. PRE AMP P.C BOARD BLOCK ................................ 65
9. NR P.C BOARD BLOCK ..................................... 65
10. MIC P.C BOARD BLOCK .................................... 65
ll. COUNTER PC BOARD BLOCK ............................... 65
12 METER PC BOARD BLOCK .................................. 65
13. LED P.C BOARD BLOCK .................................... 65
l4.BIASP.CBOARDBLOCK...............................:.... 65
15. ASSEMBLY BLOCK ......................................... 66
I6. FINALY ASSEMBLY BLOCK ................................. 67
INDEX ....................................................... 68

Resistor and Capacitor which is not listed in this parts list, please refer to
COMMON LIST FOR SERVICE PARTS.

PARTS LIST GX-747dbx

( (4- 44, /.. -./

55