4, Dbx Nr P.c Board Adjustment - Akai GX-747 dbx Service Manual

4. dbx NR PC BOARD ADJUSTMENT
NOTICES
capacitor 10/25V).
i
1. Adjustment of the dbx NR is not required except
when a part is replaced or an adjustable VR is
turned by mistake.
2. Since an error will be caused in the zero point
level and detected time constant, when the dbx
NR power supply voltage is not normal, be sure
to adjust accurately.
3. Be specially cautious for the replacement of R22,
R49 (22
M
ohms), C17, and C33 (tantalum
0
0
Since the values of R22 and R49 are as high as 22
Mohms, be cautious about dirt, flux, frost, etc.
When C 17 and C33 of small dielectric strength are
used, misoperation can sometimes occur due to a
change in leakage current.
4. In
R.M.S
symmetry adjustment (step 2), Observe
the signals at the testpoints (TP 3 to TP 6) by
refering to Fig. 9-8. Due to the signals at those
testpoints are very low level.
o
0
8
~~
l!Jo
-:i~
LIN
RCH LCH RIN
RCH LCH VR3b VR3 LOUT
~
0 0 n n 0001C4nr
I . no
I
ROUT
TP6~
,c,
VRlbo
v.,
,c,u~TP5 TP4~ LJ' c • u
y "
J~~::
1
i
r.n
y:xJ
15tt
L OUT
•~~c
2
,ca ,c~~" Ic• ,cs , c :~H
c=G: : ' . ~ : : ' . : c D: ' . :
7
=::i R ouT
RCH
VR2b VR5b
00
0
VR I ENCODER V.C.A SYMMETRY
VR2 ENCODER R.M.S SYMMETRY
VR3 DECODER V.C.A SYMMETRY
VR4 DECODER R.M.S SYMMETRY
VR5 ENCODER ZERO POINT
VR6 DECODER ZERO POINT
VR7 POWER SUPPLY
LCH RCH
00~
VR5 VR2 VR4b VR6b
i- VRlb
to
VR6b IS l NDICATE RIGHT
CHANNEL
·X· EACH TEST POINT IS USEING
. JUMPER RESISTER
Fig. 9-6 dbx Noise Reduction P.C. Board Adjustment point & Test point
STEP
ADnJSTMENT INPUT SIGNAL • TEST POINT
i
ADJUSTMENT
RESULT RE!v.1ARKS
ITEM • • POINT
I
I
Adjust so that TP-1 out-
TPI VR7 10KB put voltage becomes
Power Supply
±11.6±0.IV.At this
See l'.'lote 2.
I
time, make sure that
TP2 TP-2 voltage is within
I
-11.6±0.4V.
•
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