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Toshiba SB-420 Service Manual
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TOSHIBA
STEREO
AMPLIFIER
SB-420
Continuous O utputt
(Both Channel p rivenj
Disprtiorifåeters:
y
Prequenq
Chatecteri$ti@i}•
OutpUt Band
Re$iduåt Noise
b"rnpjng
Spea9F'Jmpédanc
SPECIFICATIONS
42W
45w
45w
-140) sswvssw
Higher HaemohiC Distortion
0.3% (at
Output)
0.05% (at iW
CrossModulation Distortion
0.3% (at ratedpugyuti,
0.05%
p gtput)
gokHi
5—40
80th
ChannelDtivem
1
(50 kS2)
MaiÄ1nV (80b
MinG
40
SERVICE
FILE
SASS 'fioOHi/QiO d B,
TREBLE
LOW
Filter:
HIGH 8
-
dB,
MUting,
dB 000 Hi)
COOdnesControV;
Equalizer
(30 —15
•PHONOMaxäAllowd3te:
-co-iigher
$N Ratio;
Mie-Atnp!fié€
AC1209
DATA
170-033
NO.
4WHz.
kHzÜ
dB
3$OtrvV
"A networ*)

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Summary of Contents for Toshiba SB-420

  • Page 1 SERVICE DATA 170-033 FILE TOSHIBA STEREO AMPLIFIER SB-420 SPECIFICATIONS SASS 'fioOHi/QiO d B, 4WHz. Continuous O utputt TREBLE (Both Channel p rivenj -140) sswvssw Filter: HIGH 8 Disprtiorifåeters: Higher HaemohiC Distortion 0.3% (at Output) MUting, dB 000 Hi) kHzÜ COOdnesControV;...
  • Page 2 SB—420 CONTENTS TECHNICAL POINTS 3 to 4 OPERATING CONTROLS FRONT VIEW REAR VIEW DISASSEMBLY INSTRUCTIONS CIRCUIT ADJUSTMENT POWER TRANSISTOR IDLING CURRENT ADJUSTMENT LEVEL DIAGRAM BLOCK DIAGRAM EXPLODED VIEW (CABINET) . 10 P.c. BOARD PART LOCATIONS Figure 16. Power Amp. P.C. Board (CCT-PA-C16) Figure 17.
  • Page 3 SB—420 1. TECHNICAL POINTS PARALLEL PUSH-PULL Figur I show commo pure complementar output circuit. Connecting these circuit inparallel composes such a circuit asshownin figure2. This circuit is calledparallelpush-pull. Para- push provide anecessar output signal using a transistor which h as notenough collector loss to obtain a necess output s ignal.
  • Page 4 SB-420 POWER ON-OFF SHOCK NOISE MUTING CIRCUIT This circuit mutesthe amplifier whenthe powerswitch is turnedON and protectsthe speaker f rom click noise. Capacitor C l startscharging by the currentflowingthroughresistor R4 immediately a fter the powerswitchis turnedON,andtransistors T R3 andTR4areturnedONby thecurrentpassirig t hroughresistor R 3. Inputsignal (Clicknoise)is dividedby internal r esistance of RI andTR4,andof R2andTR3 to lowertheoutputlevel.The...
  • Page 5 SB—420 2. OPERATING CONTROLS FRONT VIEW Treble Control Knob Balance Control Knob Treble Turn-over Selection Knob Function Knob Bass Turn-over Selection Knob Muting Knob Bass Control Knob Power Knob Volume Control Knob Headphones Jack Mic. Level Control Knob Microphone Jack Speakers Selection Knob Duplicate...
  • Page 6 SB—420 INSTRUCTIONS DISASSEMBLY BOTTOM COVER REMOVAL COVER REMOVAL Remove five screws Remove four screws See figure 8. See figure 7. Top Cover Bottom Cover Figure 8 Figure 7 FRONT PANEL REMOVAL I. Pull out the seven knobs See figure 9. Figure 9 Remove screws...
  • Page 7 SB—420 4. CIRCUIT ADJUSTMENTS POWER TRANSISTOR IDLING CURRENT ADJUSTMENT Whilethere is no signal(Connect 8 ohmwhen loading),connecttesterto TPOOI a ndTP002on poweramp.P.C. Boardand rotate and adjust semi-fixedresistorsVR005 and VR006 so that the readings on tester is values described below. Reading on tester When radiator is warmed...
  • Page 8 SB—420 DIAGRAM LEVEL (18.3 25.2dB MIC.MIX. REC.OUT MAIN IN TUNER 15 OmV REC OUT PLAY 48.0 dB (dB/V) MAI N (4mV ) (2.5 mv) pHONO 1.2 —80 -100 Figure 13...
  • Page 9 TONE CONTROL FUNCTION AMPLIFIER EQUALIZER TREBLE FILTER AMPLIFIER MUTING PHONO MODE H IGH LOW LOUDNESS MAIN REC PRE MAIN AMPLIFIER CIRCUIT TUNER MUTING BREAKER DUPLICATE S 70 PLAY MONITO IBALANCE SIOa BASS50b VOLUME MAIN AMPLIFIER PLAY2 CIRCUIT 8S8b BREAKER OUT OUT IN NODE HIGH DUBBING...
  • Page 10 SB—420 SB—420 PARTS LOCATIONS P.C. BOARD 0000 'Sisssv c 29 R 33 •s 13 ROTO c056> 0.013. 0.0'S 2 sc.oooo• c 039 c03' "022 2scj...-oR 3.3K eosi ootg cost 0082' CO'7 0015' COT O C039 '00"'0 2SC'Æ-G 72 _o Figure 18. Bottom View of Tone Amp.
  • Page 11 DIAGRAM SCHEMATIC o.o.g NE-UNIT 2SA493•GR Not" COSI PHONO' SOURCE S 20 —b Monitor — Mad. STEREO S 60 cool — Muting m 00 Loudn•s• 0082* Sloe OEEEAT CO'S Mixing SPEAKER-A colt 2SC168'-GR VROOlo—b 2SC16ze-Y coso Maim VR002 2SA493-GR v R0030—b 'TREBLE) VR004 "R 0051...
  • Page 12 SB—420 SB-420 PARTS LIST Symbol No. Part No. Description Symbol Part Description Symbol No. Part Description Part Description Symbol NO. C009, 010 22321077 Polypropylene, 3900pF, IOOV, Diode, IS1555V CAPACITORS TRANSISTORS DIODES Diode, IS1555V D007, 008 G=±2%, Z--20+80%, coil, 22381 101...
  • Page 13 SB—420 Description Symbol Part Description Symbol No. Part 1.2K 22K ohm R013, 014 22545122 R089, 090 22545223 R015, 016 22545123 12K ohm 22545152 I .5K ohm R091 , 092 R017, 22545102 1K ohm R093, 094 22545272 2.7K 2>545102 R019, 020 22570105 56K ohm, 1/4W, Metal Oxide Film 1K ohm...
  • Page 14 SB—420 Description Symbol Part 250K ohm, Variable 22651429 VR002 100K ohm, Variable VR003 22651431 100K ohm, Variable 22651431 VR004 I K ohm, Semi-fixed VR005, 22658186 50K ohm, Variable (With Sl 1) VR007 22624400 CABINET PARTS 22841 Cover Screw, M4 x 6mm 22707040 Tapping Screw, M3 x 8mm 22701326...