Realistic STA-78 - Alignment Instructions; Audio Circuit Adjustment and Check

6.
ALIGNMENT
INSTRUCTIONS
AUDIO CIRCUIT
ADJUSTMENT,/CHECK
EOUIPMENT
REOUIRED
1.
DC
Voltmeter
2.
Audio
Oscillator
3.
Oscilloscope
4. AC
Voltmeter
Note:
"Maintain
voltage at
12O
volts AC, 60
Hz
(UL,
CSA)
(240
volts, 50
Hz
AC
for Australian
models).
*Set
SELECTOR
Switch
to
AUX.
*Set
MODE
Switch
to
STEREO.
"See
P.C.B.
illustration
for
alignment
points/adjustments.
For location of connection
points
and
trimmer
resistors, see
P.C.B.
view.
(-25mV
to+25mV)
Figure 6
Oscilloscoge
(Shorled
OutpuiCondition)
(Normol
Condiiion)
Figure
5
MAIN
AMP
ADJUSTMENT
STEP
ADJUSTMENT
EOUIPMENT CONNECTION AUDIO
FBEO.
LEVEL
ADJUSTMENT
1
Check
Balance
by
measuring DC voltage
across Output
Termi-
nal
of L
and
R
chan-
nel.
DC
Volt
Meter
See
Figure
1
No
signal
DC voltage should
be
less than 25
mV
2
ldling current
adjust-
ment
DC
Volt
Meter
See
Figure
2.
No
signal
Adjust
so
voltage
across
Emitter
resistors
R633
anc
R634 is
5
mV
(8
ohm
load).
VR601
VR602
Figure
CHECKING
LIMITER CIRCUIT
STEP ADJUSTMENT EOUIPMENT CONNECTION
AUDIO
FREO SETTING
LEVEL
1
Audio Osc.
V.T.V.M.
Oscilloscope
See
Figure
3.
1000
Hz VOLUME:
Max.
BASS,
TREBLE
BALANCE:
center
Adjust input to
AUX to
get
out-
put
level
at
just
the
clipping
point
(4
ohm
load)
Figure 4.
2
Check the
limiter
ci rcu i
t.
Audio Osc.
V.T.V.M.
Oscilloscope
See
Figures
3,
5.
1000
Hz
Same
as above
Check
that output
dropt to a square
wave across
R633
(R634)
when
out-
put
speaker
termi-
nals
are
shorted.
See
Figure
6.
4ohm L.od
,A-.\
-(y
o
{c
]- +)
AUDIO
Osc.
AUX SrA-79
(
rooHz)
Figure 3
Oscilloscope
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