Realistic STA-78 User manual

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STA.78
AM /FM STEREO
Catalog Number :
RECEIVER
31-2077
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CONTENTS
ELECTRICAL PERFORMANCE SPECI FICATIONS
DISASSEMBLY INSTRUCTIONS .
PAGE
3-5
BLOCK DIAGRAM
DIAL STRINGING
LEVEL DIAGRAM
ALIGNMENT INSTRUCTIONS
TROUBLESHOOTI NG
BRIEF DESCRIPTION OF PROTECTOR CIRCUIT
IC & TRANSISTOR LEAD IDENTIFICATIONS
AM/FM TUNER, IF & MPX P.C.B. (TOP & BOTTOM VIEWS) ....18
PHONO EOUALIZER AMP P.C,B. (TOP & BOTTOM VIEWS) .....19
TONE CONTROL P.C. B. (TOP & BOTTOM VIEWS) . . .2O
MAIN AMP P.C.B. (TOP & BOTTOM VIEWS) ,...,.21
swrTCH P. C. B. (TOP & BOTTOM VTEWS) ...22
NOISE MUTING P.C.B. (TOP & BOTTOM VIEWS) ,,.23
POWER SUPPLY P.C.B.(TOP & BOTTOM VIEWS) ,,,..,,,23
ELECTRICAL PARTS LIST
EXPLODED VIEW PARTS
IC INTERNAL DIAGRAM
5
6
1
7
12
16
16
17
DIAGRAM
8-
13-
33-35
36-37
38-39
{
{t
I
{
SCHEMATIC DIAGRAM
EXPLODED VIEW
-2-

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1. ELECTRICAL PERFORMANCE SPECIFICATIONS
AM BAND
Frequency Coverage
IF
Usable Sensitivity for S/N 20 dB at 600 kHz
at 1000 kHz
at 1400 kHz
S/N Ratio at 5 mV/m input 1000 kHz
Selectivity at 1000 kHz a. 10 kHz
input = S/N 6 dB Sens. input
AGC Distortion at 1000 kHz, 80% mod. 100 mV/m input
AGC Figure of Merit
lF Rejection Ratio at 600 kHz
lmage Rejection Ratio at 1400 kHz
Bandwidth at 6 dB down
Distortion at 5 mV/m input, 30% mod.
Tape out Level at 5 mV/m input (RCA)
Tape out Level at 5 mV/m input (DlN)
Fidelity Bandwidth at 5 mV/m input (1 kHz = 0 dB)
Whistle Modulation of 2nd and 3rd harmonic, at 1 mV/m,
5 mV/m and 100 mV/m input
Dial Calibration at 600 kHz
at 1400 kHz
Overload: With a radiated signal of 1Ylm, the signal shall
breakup.
FM BAND
Frequency Coverage
IF
IHF Sensitivity at 90 MHz
at 98 MHz
at 106 MHz
New IHF
S/N 50 dB Ouiting Sensitivity at 90, 98 and 106 MHz
S/N Ratio at 'l mV input
3 dB Limiting Sensitivity
lF Rejection Ratio at 90 MHz
lmage Rejection Ratio at 106 MHz
Spurious Response and Cross Modulation
Capture Ratio
Alternate Channel Selectivity 100 pV input
Distortion at 1 mV input
Dial Calibration at 90 MHz
AFC Holding Range at 1 mV input
Temperature Range for Satisfactory operation
AM Suppression
Maximum Signal Handling Capacity
Tape out Level at 1 mV input (RCA)
Tape out Level at 1 mV input (DlN)
UNIT
kHz
kHz
pV lm
pV lm
pY lm
dB
dB
o/
/o
dB
dB
dB
kHz
o/
/o
mV
mV
Hz
%38
kHz 0 r,25
kHz 0 4.50
tunable without undue distortion or
32 25
48
50 42
35 28
45 38
6 4.5-9
0.8 2
200 200 *.2.5 dB
15 15 r 2.5 dB
50-2200 B0-1800
NOMINAL
510-1650
455
200
200
200
45
LIMIT
520-1620
500
500
500
40
be
UNIT
MHz
MHz
pV
pV
pV
dBf
pV
dBf
dB
pV
dB
dB
dB
dB
dB
o/o
kHz
kHz
"C
dB
mV
mV
mV
NOMINAL
86.5-109
10.7
1.9
1.9
1.9
10.8
2.8
14.2
65
1.8
85
5B
80
1.5
60
0.1
a.250
LIMIT
88- 1 0B
3.8
3.8
3.8
16.8
4.5
18.2
55
3.5
70
48
65
4
48
0.5
1 250
t250 +. 100
0-45
42
100
750 .t. 2.5 dB
15 a.2.5 dB
50
200
750
15
-3-

Muting Sensitivity
F requency R esponse ( De-emphasis)
75 pS (UL & C.S.A.)
50 pS (Australian)
25 pS (for FM Dolby)
All sets must meet the requirements of the FCC, FTZ.
FM STEREO BAND
Stereo I ndicator Sensitivity
Stereo Separation at 1 mV input
Stereo Distortion at 'l mV, 1 kHz
Pilot and Sub-carrier Leakage
AUDIO SECTION
at 100 Hz
at 1 kHz
at 10 kHz
input
lnput lmpedance PHONO MAG.
AUX
TAPE IN
Output Power, TH D 0.5% from 20 Hz to 20 kHz,
I ohms Both Channel Driven
Output Power, THD 0.5% at 1 kHz Both Channel Driven
Distortion at 5 W from 20 Hz to 20 kHz
Sensitivity for Rated Power (22W\
PHONO MAG.
AUX
TAPE IN
Frequency Response at AUX from 20 Hz to 20 kHz input,
1 W output
Bass Action at 100 Hz
Treble Action at 10 kHz
Min. Volume Hum & Noise
Signal to Noise Ratio PHONO MAG. (lnput shorted)
AUX (lnput 10 Kohm terminated)
TAPE lN (lnput 10 K ohm terminated)
Cross Talk at 1 kHz AUX Position
Loudness contour ch. at 100 Hz -30 dB Vol. position
Loudness contour ch. at 10 kHz -30 dB Vol. position
Channel Balance at AUX, Vol. = Max.
TAPE OUT Level PHONO MAG. (RCA)
AUX, (RCA)
PHONO MAG. Equalizer Response at 100 Hz
at 10 kHz
PHONO MAG. Over Load (THD = 0.5%)
DC Balance
UNIT
pV
dB
dB
dB
NOMINAL
5.5
UNIT
pV
dB
dB
dB
o/
/o
dB
UNIT
K ohm
K ohm
K ohm
NOMINAL
5.5
3B
48
35
0.5
50
NOMINAL
50
50
50
25
27
0.15
2.2
160
160
F lat
a.10
i.10
1
65
75
75
55
+9
+4
150
150
+ 13.1 1
-13.75
120
0
LIMIT
3.5-9.0
*1ae
_J
*1 oa
_J
1l an
LIMIT
3.5-9.0
28
33
28
1.5
45
LIMIT
22
24
0.3
2.2t3dB
160f3dB
160r3dB
*-2
a.10 L 2.5
r_10 i.2.5
3
55
65
65
45
+9 i 2.5
+4 r.2.5
r-2
150 r 3 dB
150 i.3 dB
*.2 dB
r_2 dB
90
*.30
W
W
o/
/o
mV
mV
mV
dB
dB
dB
mV
dB
dB
dB
dB
dB
dB
dB
mV
mV
dB
dB
mV
mV
-4-

Note:
The supply voltage is 120 volts AC (for UL & C.S.A.) and 24O volts AC for Australian models,
from a regulated power supply.
The power source must be insulated from other equipment connected antenna or output. The room
temperature is 25 degrees C.
Nominal Specs represent the design specs; all units should be able to approximate these - some will
exceed and some may drop slightly below these specs.
Limit Specs represent the absolute worst condition which still might be considered acceptable; in
no case should a unit perform to less than within any Limit Spec.
2. DISASSEMBLY INSTRUCTIONS
1) To remove Chassis f rom wooden cabinet.
Turn the cabinet upside down and re-
move the six screws from the bottom
cabinet. (Figure A)
2) Removal of Front Panel.
a) Remove the chassis from wooden
b) Pull out the Main Chassis.
c) Remove the two screws from the top
d) Remove knobs and pull off panel.
Figure A
cabinet as described in 1).
and three screws from the bottom of
(F igure B1 , B2l the Front Panel.
3)To remove Rear Panel from chassis.
Remove the four screws from the Rear
Panel. (F igure C)
Figure B1 Figure 82
-5-

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3. BLOCK DIAGRAM
-6-

4. DIAL STRINGING DIAGRAM *START WITH CAPACITOR SET AT MINIMUM.
PLATES FULLY OPEN (UNMESHED).
*Pointer Position : HIGH END
@
5. LEVEL DIAGRAM
F
I
AUDIO FREQIJENCY. lkHz
-7-

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 1No 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
<-7>
\1J
-8-

AM RF & IF ALIGNMENT
EOUIPMENT REOUIRED
1. AM Signal Generator
2. AC Voltmeter
3. Oscilloscope
4. Distortion Meter
Figure 7
Note: *Signal generator output should be no higher than necessary to obtain an output reading.
*Maintain line voltage at 12O volts, 60 Hz AC (UL & CSA) (240 volts, 50 Hz AC for Australian
models).
"Set SELECTOR Switch to AM.
*See P.C.B. illustrations for alignment points/adjustments and Figure 7.
osclLloscoPE DtsToRTloN
AC VOLTMETER METER
TAPE OUT
(LorR)
Figure 8
-9-
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STEP SIGNAL GENERATOR
COUPLING SIGNAL GENERATOR FREOUENCY DIAL SETTlNG INDICATOR ADJUSTMENT REMARKS
1
Connect standard loop
ANTENNA to Signal
Generator and radiate
signal into the AM Fer-
rite Antenna.
See Figure 8.
455 kHz
(400 H2,30% mod.) Point of
non-inter-
ference
(near
600 kHz)
Scope and,
AC Volt-
meter to
TAPE OUT
Jack.
r202
T203
(AM IFT)
Adjust for maxi-
mum reading on
meter.
2
Same as STEP 1. 510 kHz
(400 H2,30% mod.) Tuning
Gang
fully
closed.
Same as
STEP 1. L2O3 (AM OSC Coil) Adjust for maxi- mum reading on
meter. Refer to
Figures 7 and 8.
3
Same as STEP 11650 kHz
l4OO H2,30% mod.) Tuning
Gang
fully
opened.
Same as
STEP 1. TC105 (AM
OSC Trimmer) Adjust for maxi- mum reading on
meter. Refer to
Figures 7 and 8.
4
Same as STEP 1600 kHz
(400 H2,30% mod.) 600 kHz Same as
STEP 1. L8O2 (AM ANT. Coil) Adjust for maxi-
mum reading on
meter. Refer to
Figures 7 and 8.
5
Same as STEP 11400 kHz
(400 Hz, 30% mod.) 14OO kH,z Same as
STEP 1. TC104 (AM
ANT. Trimmer) Adjust for maxi- mum reading on
meter. Refer to
Figures 7 and 8.
6Repeat STEPs 4 and 5 until no further change is noticed.
7
Same as STEP 11000 kHz
(400 kHz,30% mod.)
Output level to
100 mV/m
1000 kHz AM Signal
Meter on Set. VR201 Adjust so the
Meter Pointer
on Receiver is
at about 85%
of full scale.
2 -__.4 AM BAR ANTENNA
(6ocm) L/
\ l/_
/ffi @wfl

FM RF & IF ALIGNMENT
EOUIPMENT REOUIRED
1. FM Signal Generator
2. AC Voltmeter
3. Oscilloscope
4. Distortion Meter
5. CenterTuning Meter (1.2K ohm,200pA)
Note: "Signal Generator output should be no higher than necessary to obtain an output reading.
*Maintain line voltage at 120 volts, 60 Hz AC (U L & CSA) (240 volts, 50 Hz AC for Australian
models).
"Set SELECTOR Switch to FM.
"Refer to P.C.B. illustration and Figure 7 for test points/adjustments.
STEP GENERATOR
COUPLING GENERATOR
FREOUENCY D!AL
SETTING INDICATOR ADJUSTMENT REMARKS
1
Signal Generator to
FM Antenna Termi-
nal thru FM Dummy
Antenna (300 ohm)
98 MHz
(400 Hz
75 kHz dev.)
lnput: about
2-3 ttY
Near
98 MHz AC Voltmeter.
Scope and Dis-
tortion meter
to TAPE OUT
Jack (L or R).
T101 Adjust for maximum
reading on meter.
Refer to Figure 1 1.
2
Same as STEP 198 MHz
(400 Hz,
75 kHz dev.)
lnput: no input
(unit off )
Near
98 MHz Connect the
Center Tuning
Meter (1.2 kO,
200 pA) to Pin
No.12(+)and
No.13(-)on
AM/FM IF
Board (Refer
to Figures 7
and 9A.)
T201
(Primary) Adjust for Center
point on Center Tu-
ning Meter.
Refer to Figures 9,
9A, 10 and 1 1.
3
Same as STEP 198 MHz
(4OO Hz,
75 kHz dev.)
lnput: 1 mV
Same as
STEP 1. AC Voltmeter,
Scope and Dis-
tortion Meter
to TAPE OUT
Jack (L or R).
T201
(Secondary) Adjust for minimum
Distortion (about
0.1%). Refer to
Figure 9, 10 and 1 1.
4Repeat STEPs 1 ,2 and 3 until no further improvement is noticed.
5
Same as STEP 1. 90 MHz
(40O Hz,
75 kHz, dev.)
lnput: about
2-3 ttY
90 MHz Same as
STEP 1. L101 (FM
Antenna Coil)
1103 (FM RF
Coil-stretch or
squeeze)
Ll05 (FM OSC
Coil)
Adjust for maximum
reading on meter.
Refer to Figures 7
and 1 1.
b
Same as STEP 106 MHz
(400 Hz,
75 kHz dev.)
lnput: about
2-3 ttY
106 MHz Same as
STEP 1. TC 101(FM Antenna Trim-
mer)
TC1O2 (FM RF
Trimmer)
TCl03 (FM OSC
Trimmer)
Adjust for maximum
reading on meter.
Refer to Figures 7
and 1 1.
7Repeat STEPs 5 and 6 until no further improvement is noticed.
8
Same as STEP 198 MHz
(400 Hz,
75 kHz dev.)
lnput: 5 trrV
98 MHz Same as
STEP 1. VR2O3 "MUTE" switched
"ON" and adjust
VR203 for no signal
output.
ISame as STEP 198 MHz
(4OO Hz,
75 kHz dev.)
lnput: 100 mV
98 MHz Signal Meter
on Set. vR202 Adjust so the Meter
Pointer on Receiver is
about 90% of full-scale.
-10-