Akai GX-747 dbx Service Manual

STEP
2
3
4
5
ADTIJSTMENT
ITEM
R.M.S
Symmetry
V.C.A
Symmetry
ZERO
Point
Confirmation
of ENCODER
and
DECODER
Operation
I
INPUT SIGNAL
100
Hz
-5.5 dBm
(410 mV) from
an oscillator
1000 Hz,
-5.5 dBm
(410 mV) from
an oscillator
1000 Hz,
-5.5 dBm
(410 mV) from
an oscillator
lOO0Hz,
-5.5 dBm
±10
dB from
an oscillator
TEST POINT
TP-5 (L)
TP-6
(R)
(ENCODER)
TP-3 (L)
TP-4 (R)
(DECODER)
Each
ENCODER/
DECODER
Output
Terminal
Each
ENCODER/
DECODER
Output
Terminal
Each
ENCODER/.
DECODER
Output
Terminal
I
I
ADJUSTMENT
RESULT
POINT
Observe TP3
to TP6
VR2 50kB
with an oscilloscope,
(ENCODER)
and adjust with VR2
and VR4 (50 KB) so
VR450kB
that the peak value
of
(DECODER)
the waveform becomes
constant at 200 Hz.
VRI 50 kB
Adjust VRI (encoder)
(ENCODER)
and VR3 (decoder)
so
that the distortion at
VR3
50kB
each terminal is mini-
(DECODER)
mized (below 0.1%).
YRS 500
kB
Adjust YRS (encoder)
and VR6 (decoder)so
(ENCODER)
that the output level
of
each output terminal
corresponds
to the in-
VR6 500
kB
put at -5.5 dBm (410
(DECODER)
mV).
Make sure that during
encode and decode,
compression and ex-
pansion
are made in
Confirmation
the proportion
of 2
to 1, when the input
signal level
is changed
by ±10 dB. (See Fig.
9-8)
---T -
PEAK VALUE
______ J_
1
5ms
1
~200Hz--;;,.f
Fig. 9-7 Oscilloscope Waveform
dBx NR P.C.B
V.T.V.M
OSCILLOSCOPE
,~,
TP3 to TPS
11\f'v
I
IN OUT
Q
,...
-
-
-
-
-
~
-
-
-
Fig. 9-8
REMARKS
Refer to Fig.
9-7.
See Note 4.
Fig. 9-8
Refer to Fig.
9-8.
INPUT LEVELS
ENCODER OUTPUT LEVEL
DECODER OUTPUT
LEVE, L
-15.5 dBm
-10.5 dBm
-25.5 dBm
-5.5 dBm
-5.5 dBm
-5.5 dBm
+4.5 dBm
-0.5 dBm
+14.5 dBm
* Tolerance of each output is ±3 dB.
---------------SERVICE MANUAL GX-747dbx ---------------
40

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