Realistic STA-21 User manual

STA.21
AM /FM STEREO RECETVER
Catalog Number : 31 -2071
cusT0M MANUFACTURED FOR RAD|0 SHACK [ln DMS|0N 0F TANDY C0RP0RAT|0N
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(1} ELECTRICAL PERFORMANCE SPECIFICATIONS ..... 3 -
(2} DISASSEMBLY INSTRUCTIONS .
(3) BLOCK DIAGRAM
(4) ALIGNMENT INSTRUCTIONS .,. 7 -
(5) TROUBLE SHOOTING . . , 12 -
(6) DIAL STRINGING DIAGRAM
(7) IC & TRANSISTOR LEAD IDENTIFICATION .
(8) AM/FM TUNER, IF & MPX ASSEMBLED BOARD
(TOP & BOTTOM VIEWS)
(9) PRE & TONE AMP ASSEMBLED BOARD
(TOP & BOTTOM VIEWS)
(10) MAIN AMP & POWER SUPPLY ASSEMBLED BOARD
(TOP & BOTTOM V|EWS) ....... 18
(11) JACK ASSEMBLED BOARD
(TOP & BOTTOM VTEWS) ....... 19
(12) ELECTRICAL PARTS LIST . , . ,. 19 - 27
(13) EXPLODED VIEW PARTS LIST . 28 - 30
(14) IC INTERNAL DIAGRAM ...... 31
(15) SCHEMATIC DIAGRAM . 32 - 33
(16) EXPLODED VIEW 34 - 35
4
5
b
11
14
15
15
16
17
-2-

1. ELECTRICAL PERFORMANCE SPECIFICATIONS
AM BAND
Range
IF
Antenna Sensitivity for S/N 20 dB
at 600 kHz
at 1000 kHz
at 1400 kHz
Terminal Sensitivity (20 dB S/N)
ACA at S/N 6 dB sensitivity at 1000 kHz
AGC Distortion at 1000 kHz, 100 mV/m, 80% Mod.
AGC Figure of Merit
lF Rejection at 600 kHz
lmage Rejection at 1400 kHz
Distortion at 5 mV/m 30% Mod.
Tapeout Level at 5 mV/m 30o/o Mod. 400 Hz
Fidelity 5 mV/m lnput, -6 dB Down (1 kHz:0 dB)
Whistle Modulation of 2nd and 3rd Harmonic
atland5mV/m
Calibration Accuracy at 600 kHz
at 1400 kHz
FM BAND
Range (For UL and C.S.A. Models)
Range (For European and Australian Models)
IF
IHF Sensitivity at 90, 98 and 106 MHz
FM S/N Ratio at 98 MHz, 1 mV lnput
FM Limiting -3 dB
lF Rejection at 90 MHz
lmage Rejection at 106 MHz
Capture Ratio
ACA + 400 kHz at 100 pV
Audio THD 400 H2,75 kHz Dev.
Audio THD 400 H2,22.5 kHz Dev.
Calibration Accuracy at 90 MHz
at 106 MHz
AFC Holding Range with 1 mV Signal
AM Suppression
Maximum Signal Handling Capacity
Tapeout Level 1 mV 75 kHz Dev. 400 Hz Mod.
All Sets must meet the Requirements of the FCC.
UNIT
(kHz)
(kHz)
I pV /ml
( zV)
(dB)
(o/ol
(dB)
(dB)
(dB)
l'/ol
(mV)
(Hz) 50
(o/ol
(kHz)
(kHz)
UNIT
(MHz)
(l.VlHz)
(MHz)
( pYl
(dB)
( pV)
(dB)
(dB)
(dB)
(dB)
lo/ol
(o/ol
(kHz)
(kHz)
(kHz)
(dB)
(v)
(mV)
NOM INAL
510 - 1650
455
200
200
200
10
28
4
45
32
45
1.5
250
- 2500
LIMIT
520 - 1620
500
500
s00
NOMINAL LIMIT
86.5 - 108.5 88 - 108
87.5 - 108.5 87.5 - 108
10.7
2.8
60
3.2
80
50
3
45
0.5
0.3
+ 200
38
0.2
750
20
10
38
27
35
3.5
200
10
t25
+50
;:;
55
7.1
70
45
6
30
1.0
0.8
t 500
+ 500
300 - 800
30
0.1
750 + 2.5 dB
:
Frequency Response must meet the 75 1-usec.De-emphasis for UL and C.S.A. Approved Models
(50 p sec.De-emphasis for European and Australian Models).
-3-

FM MPX
Stereo lndicator "ON" Point
Separation at 1 mV 100 Hz
1 kHz
10 kHz
Stereo Distortion 1 mV 1 kHz
38 kHz Rejection
SCA Rejection
AUDIO SECTION
lnput lmpedance PHONO MAG.
AUX
Output Power at THD 1% 8 ohms
Both Channels Driven at 1 kHz
Power Bandwi<ith B ohrns Both Channels Driven
TH D 1 o/o, 20 Hz - 20 kHz
Sensitivity for Rated Power
PHONO MAG.
AUX
Tape ln
Frequency Response at AUX (1 W t 2 dB)
Bass Action at 100 Hz
Treble Action at 10 kHz
Min. Volume Hum and Noise
Max. Volume Hum and Noise Tone Max. at AUX
Signal to Noise Ratio
PHONO MAG. 5 mV Input (lnput Short)
AUX 200 mV lnput
Cross Talk at 1 kHz AUX
Bass Compensation at 100 Hz -30 dB Volurne
Treble Compensation at 10 kHz -30 dB Volume
Tapeout Level PHONO MAG. at 3 mV 1 kHz
AUX at 200 mV 1 kHz
PHONO MAG. Eq. Response at 100 Hz
at 10 kHz
Tapeout Level (DlN Connector)
AM 5 mV,/m lnput 30% Mod.
FM 1 mV lnput 22.5 kHz Dev.
AUX 200 mV lnput
PHONO MAG. Overload
NOTE:
UNIT
( ,,rV)
(dB)
(dB)
(dB)
lo/ol
(dB)
(dB)
UNIT
(K ohm)
(K ohm)
(w)
(w)
(mV)
(mV)
(mV)
(Hz) 15
(dB)
(dB)
(mV)
(mV)
(dB)
(dB)
(dB)
(dB)
(dB)
(mV)
(mV)
(dB)
(dB)
(mV)
(mV)
(mV)
(mV)
NOMINAL
10
29
34
26
0.6
42
42
LIMIT
20
?2
27
20
2.0
35
35
NOMINAL
50
100
11
8.5
2.5
150
't50
-30K
+10
+10
1
15
60
65
46
+9
+4
200
200
+13
-13
LIMIT
8.5
25
25
25
80
7
3.5
200
200
20-20K
t 10 t2.5
t 10 +2.5
3
70
55
55
40
+9 +2
+4 X2
200 + 2dB
200 + 2dB
+13 +2
-13 +2
25 + 3dB
25 + 3dB
25 t 3dB
60
The supply voltage is 120 volt AC (for UL and C.S.A. Models) (use 220/240 volt AC for European
and Australian Models), from a regulated power supply. The Power Source must insulated from
other equipment connected to 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 Specs.
-4-

2. DISASSEM BLY I NSTR UCTIONS
1)To remove chassis from wooden
cabinet.
Turn the cabinet upside down and
remove the five Pan head screws from
the cabinet bottom.
2) Removal of front panel (Aluminum
panel )
a) Remove the chassis from wooden
cabinet as described in 1).
b) Pull out the main chassis.
c) Remove the two Pan head screws from
the top and the three Pan head screws
from the bottom of the front panel.
d) Remove knobs and pull off panel.
3) To remove rear panel from chassis.
Remove the four Pan head screws from
the rear panel.
-5

3. BLOCK DIAGRAM
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-6-

4. ALIGNMENT INSTRUCTIONS
MAIN AMPLIFIER AND RESET CIRCUIT ADJUSTMENT/CHECK
NOTE o Maintain line voltage at 120 volts. (UL, C.S.A.) (Use 220/240 VAC For European & Australian Models.)
o Set SELECTOR Switch to AUX.
. Set MODE Switch to STEREO.
o See P.C.B. illustrations for alignment points/adjustments.
MAIN AMPL!FIER ADJUSTMENT
STEP ADJUSTMENT EOUIPMENT CONNECTION AUDIO FREO. LEVEL ADJUSTMENT
1
Check DC Balance
by measuring
DC voltage
across Output
of L and
R channel.
DC Volt Meter See Fig. 1No signal DC
voltage
should be
less than
30 mV.
Select of
8305(L channel)
R306(R channel)
2
ldling current
adjustment DC Volt Meter See Fig,2 No signal Adjust voltage
across Emitter
resistors R321
and R322
to 10 mV.
(8 0 Load)
R329
R330
0-30 mV
Main Amp Figure 1 (-30 mV to +30 mV)
Reset Lamp
8 ohm load
Speaker Output Oscilloscope (When protector circuit is activated)
E
Oscilloscope
Osc
Hz)
Adjust Volt Meter for 10 mV
Main AmP Figure 2
RESET CI RCU IT ADJ USTM ENT
STEP ADJUSTMENT EOUIPMENT CONNECTION AUDIO FREO. SETTING LEVEL ADJUSTMENT
1Turn trimmer resistor R 332 counterclockwise (minimum value).
2
Audio Osc.
V.T.V.M. Figure 31000 Hz VOLUME: Max
BASS, TREBLE
& BALANCE:
Center
Adjust input to
AUX 1 to get
output level
of about 3 Volts
(8 ohm load)
3
Reset circuit
adjustment Audio Osc. V.T.V.M. Figure 41000 Hz Same as
above Adjust R 332 so
output drops to zero
(RESET comes "on")
when output speaker
terminals are shorted:
DO NOT ADJUST
PAST THIS POINT.
R 332
Figure 3
-7 -
AC V.T.V.M. (3V) Figure 4

@l-"o'" "o'''''ou'
(TC 1O3)
FM OSC, TRIMMER
[mAN___r%3i*,
ta_\
Elf- FM lsr lF rr rolr
ALIGNMENT
Signal generator output should be no higher than necessary to obtain an output reading.
Maintain line voltage at 120 volts. {UL, C.S.A.} (Use 220/240 VAC For European & Australian Models.)
Set SELECTOR Switch to AM.
See P.C.B. illustrations for alignment points/adjustments.
AM ALIGNMENT SET-UP
AM INTERNAL BAR ANTENNA Scope
Figure 5
-8-
EOUIPMENT REOUIRED
1. AM Signal Generator
2. AC Voltmeter
3. Oscilloscope
AM IF&
NOTES:
TUNER COIL
rrc 101) (rc 104]
FM ANT AM ANT
TRIMMER TRIMMER
& TRIMMER LOCATIONS
(TC 102) (TC 1O5)
FM RF AM O$,
TRIMMER TRIMMER
RF
a
o
a
a
STEP SIGNAL GENERATOR
COUPLING SIGNAL GENERATOR FREOUENCY DIAL SETTING INDICATOR ADJUSTMENT REMARKS
1
Connect standard
loop ANTENNA to
Signal Generator
and radiate signal
into the AM Ferrite
antenna. See Fig. 5.
455 kHz
(4ob Hz,30% MoD) Point of non-
interference
(near 600 kHz)
AC Voltmeter
tO TAPE OUT
JACK
T 106
1 107
T 108
T 109
Adjust for
maximum
reading.
2Same as above 600 kHz (400 Hz,
30o/o MOD) 600 kHz Same as above T 105 (OSC Coil)
L 106 (AM ANT
Coil)
Adjust for
maximum
reading.
3
Same as above 1400 kHz (400 Hz,
30o/o MOD) 1400 kHz Same as above TC 105
(OSC Trimmer)
TC 104
(ANT Trimmer)
Adjust for
maximum
reading.
4Repeat steps 2 and 3 urrtil no further change is noticed.
5
Same as step 'l 1000 kHz (400 Hz,
30% MOD)
Output level
to 100 mV,/m
Point of non-
interference
and no signal
AM Strength
Meter Select
value of
R 160
Meter Pointer
on Receiver
should indicate
between 80o/o
and 90% on
the Meter.
AM SIGNAL GENERATOR 2'(60cm)- tlr)r'\
AC
VOLTMETE R@
Cf)B---
[.=-rE[!--=
STA-21
TAPE OUT (L or R)

FM RF & IF ALIGNMENT
EOUIPMENT REOUIRED 3. AC Vottmeter
1. FM signal Generator output Level: 1 mV 4. oscilloscope
2. Sweep Generator S. Distortion Meter
NOTE o Signal Generator output should be no higher than necessary to obtain an output reading.
. Set SELECTOR Switch to FM.
o Maintain Line voltage at 12Q volts. (UL, C.S.A.) 1220/240 VAC For European & Australian Models.)
a Refer to P.C.B. illustrations for test points,/adjustments.
STEP GENERATOR
COUPLING GENERATOR
FREOUENCY RADIO DIAL
SETTING INDICATOR ADJUSTMENT REMARKS
1
Sweep Generator to
"FM ANT" terminal
on FM Front end
board
10.7 MHz
(1400 kHz
Sweep)
Any dial setting
where no noise
or interference
exists
Scope to TP 7
at R 151
{MPX input)
AM/FMIMPX
Board
T 101, 102
103, 104
(Primary)
FM IFT
Adjust for maximum
amplitude and
proper linearity
between + 150 kHz
markers.
Refer to Fig. 7.
2
Sweep Generator to
FM Antenna
Terminal thru FM
Dummy antenna
(300 ohm)
T101, 102
FM IFT
3
Same as above T 104 FM IFT.
(Primary and
Secondary)
Ajust for symmetri-
cal "S" curve as
shown in Fig.6.
4
Signal Generator to
FM Antenna
Terminal thru FM
Dummy antenna
(300 ohm)
98 MHz
(400 Hz, 100o/o
MOD}
Tune for
Maximum
reading on
meter
Distortion
Meter to TAPE
OUT Jack
T 104
FM Discrim.
(Secondary)
Adjust for minimum
distortion.
5
Same as above *86.5 MHz
See Note
in step 7
Tuning gang
fully closed AC Voltmeter
and Scope to
TAPE OUT
Jack
L 105
(FM OSC} Adjust for maximum
reading on meter.
6Same as above 108.5 MHz Tuning gang
fully opened TC 103 (FM
OSC Trimmer)
7Repeat STEPs (5) and (6) until Tuning Range Covers exactly from 86.5 MHz to 108.5 MHz.
(*European models must not be able to tune below 87.8 MHz.)
8
Signal Generator to
FM Dummy
antenna (300 ohm)
90 MHz 90 MHz
Tune to
Signal
AC Voltmeter
and Scope to
TAPE OUT
Jack
L 101
(FM ANT Coil)
L 103 (FM BF
Coil; stretch
or squeeze)
Adjust for maximum
reading on meter.
9
Same as above 106 MHz 106 MHz
Tune to
Signal
TC 101 (FM
ANT Trimmer)
TC 102 (FM
RF Trimmer)
10 Repeat STEPs (8) and (9) until no further improvement is noticed.
11 Same as STEP (8)
ANT. input: 1 mV 98 MHz 98 MHz Tune to
Signal T110 Adjust for maximum
reading on meter.
12 Same as STEP (8)
ANT. input: 100 mV VR1Ol Adjust so the Meter
Pointer on Receiver
is full scale.
-9-

FM SIGNAL GENERATOR
FM ALIGNMENT SET-UP
3OOO DUMMY FM ANT
Sweep Gen-
FM STEREO ALIGNMENT
Equipment Required
1. Stereo Modulator . . .. .
2. FM Signal Generator . .
3. Audio Generator
4. AC Voltmeter
5. Oscilloscope
6. Distortion Meter
7. Frequency Counter
Note: See P.C.B. illustration for alignment/test points.
Preliminaries
Set SELECTOR switch to FM STEREO.
MULTIPLEX & SEPARATION ALIGNMENT
TAPE OUT
(L or B)
AC V.T.V-M- DISTOBTION METER
tLrpTatRlsl(470)
Figure 7
Connect Stereo Modulator to EXT. Mod. terminal FM signal generator.
Modulation Level of 19 kt{z Pilot Signal ....8 - 10 %
Output Level ... 1 mV
Frequency ....... Approximately 98 MHz
Deviation ........75 kHz 100 % modulation of composite signal
STEP SIGNAL GENERATOR
COUPLING STEREO
MODULATION INDICATOR ADJUSTMENT REMARKS
1
Connect to FM Antenna
terminal thru FM
dummy antenna(30O 0 )
Mono. 1 kHz
{1000 Hz, No Mod)
lnput 1 mV
Counter connected
to TP 14 at Pin No 12
of lC
VR 103 Adjust for 19 kHz
+50 Hz on Counter.
Refer to Fig. 8.
2
Same as above Composite MPX
Signal 1 kHz on
Left channel ONLY
AC Voltmeter
connected for
TAPE OUT
jack of Right
channel
VR 102
(Separation) Adjust for mini-
mum reading.
Refer to Fig. 9.
3
Same as above Composite MPX
Signal 1 kHz on
Right channel ONLY
AC Voltmeter
connected for
TAPE OUT
jack of left
channel
Same as above Same as above
4Repeat STEPs 2 and 3 until AC Voltmeter reading is at least -33 dB re same channel output (i.e.
33 dB separation).
5
Same as step 1Composite
Signal 1 kHz AC Voltmeter
connected to
TAPE OUT
jack
With 10 pV
antenna input signal,
stereo indicator
lamp should come on.
- 10-