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LEFT CHANNEL
DOLBY NR PC BOARD TD- 530!
5.DOLBY
NOISE
REDUCTION
ADJUST-
MENT
(Model
GX-630DB)
(Refer
to
Fig.
15)
PART-1.
RECORDING
DOLBY
N.R
CIRCUIT
ADJUSTMENT
Disconnect
the
wire
connected
to
Dolby
circuit
input
and
output
terminals
(A)
and
(B).
Connect
an
Audio
frequency
oscillator
to
terminal
(A)
and
connect
a
High-sensitivity
VTVM
to
terminal
(B).
1)
Turn
semi-fixed
resistors
VRI
IkB
and
VR2
5
kB
fully
clockwise
(Fig.
15).
2) Ground test points T.P (Fig. 15)
3) Set Dolby Switch to OFF position.
4) Supply a 5 kHz, —10 dBm signal which has been
verified with a frequency counter from the audio
frequency oscillator and confirm that at this time
the indication of the high-sensitivity VTVM con-
nected to terminal (B) is 0 dBm.
5) Reduce the output of the audio frequency oscil-
lator by —30.5 dB from the condition outlined in
item 1-4) (S kHz, —40.5 dB) and at this time
confirm that the indication of the high-sensitivity
VTVM connected to terminal (B) is —30.5 dB.
6) Set Dolby Switch to ON position and adjust
semi-fixed resistor VRI 1 kB to obtain a —-20.5
dBm indication on the high-sensitivity VTVM
connected terminal (B).
7) Disconnect ground wire from test point T.P
(grounded in item 1—2) and at this time adjust
semi-fixed resistor VR2 5 kB to obtain a —22.5
dBm indication on the high-sensitivity VTVM
connected to terminal (B).
Fig. 15
NOTE: Identical P.C Boards are utilized for Record-
ing Dolby N.R and Playback Dolby N.R
The Recording Dolby N.R P.C Board is
located on the Recording Amp P.C Board
and the Playback Dolby N.R P.C Board is
located on the Playback Amp P.C Board,
Adjust left and right channels respectively.
PART-2. PLAYBACK DOLBY N.R CIRCUIT
ADJUSTMENT
This adjustment is carried out in essentially the same
way as the recording Dolby circuit adjustment.
Disconnect the wire connected to input and out put
terminals(A’) and (B), connect and audio frequency
oscillator to terminal(A’), and connect a higi=sensi-
tivity VTVM to terminal(B). Turn semi-fixed wesistor
VRI 1 kB and VR2 5 kB fully glochide and {round
test points T.P.
1) Set Dolby Switch to OFF position and suply a 5
kHz, 10 dBm signal which has been verified with
a frequency counter from the audio frequency
oscillator, Confirm that the high-sensitivity VT "VM
indication at this time is O dBm. Next, lower the
oscillator output by —22.5 dB and confim that
the high-sensitivity VTVM indication is —21.5 dB.
2) Set Dolby Switch to ON position and at this time
adjust semi-fixed resistor VRI 1 kB to oltaän a
—32.5 dB high-sensitivity VTVM indication.
Next, disconnect ground wire from test pots T.P
and adjust semi-fixed resistor VR-2 5 kB toob tain
a —30.5 dBm indication.
Dolby
is
a
trademark
of
Dolby
Laboratories,
Inc.
Under
License
from
Dolby
Laboratories,
Inc.
15