Realistic-STA78-rec-sm 维修电路原理图.pdf

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1、ruLtsfiCSerulceSTA.78AM /FM STEREOCatalog Number :RECEIVER31-2077cusToM MANUFACTURED FoB RADIo sHACK In DMSIoN 0F TANDv conponAloNRadioFans.CN 收音机爱 好者资料库(1)(21(3)(4)(5)(6)(71(B)(e)( 10)(11)(121( 13)(141( 15)( 16)(171( 1B)( 1e)(20)(211CONTENTSELECTRICAL PERFORMANCE SPECI FICATIONSDISASSEMBLY INSTRUCT

2、IONS .PAGE3-5BLOCK DIAGRAMDIAL STRINGINGLEVEL DIAGRAMALIGNMENT INSTRUCTIONSTROUBLESHOOTI NGBRIEF DESCRIPTION OF PROTECTOR CIRCUITIC & TRANSISTOR LEAD IDENTIFICATIONSAM/FM TUNER, IF & MPX P.C.B. (TOP & BOTTOM VIEWS) .18PHONO EOUALIZER AMP P.C,B. (TOP & BOTTOM VIEWS) .19TONE CONTROL P.C. B. (TOP & BOT

3、TOM VIEWS) . . .2OMAIN AMP P.C.B. (TOP & BOTTOM VIEWS) ,.,.21swrTCH P. C. B. (TOP & BOTTOM VTEWS) .22NOISE MUTING P.C.B. (TOP & BOTTOM VIEWS) ,.23POWER SUPPLY P.C.B.(TOP & BOTTOM VIEWS) ,.,23ELECTRICAL PARTS LISTEXPLODED VIEW PARTSIC INTERNAL DIAGRAM561712161617DIAGRAM8-13-33-3536-3738-39tISCHEMATIC

4、 DIAGRAMEXPLODED VIEW-2-RadioFans.CN 收音机爱 好者资料库i1. ELECTRICAL PERFORMANCE SPECIFICATIONSAM BANDFrequency CoverageIFUsable Sensitivity for S/N 20 dB at 600 kHzat 1000 kHzat 1400 kHzS/N Ratio at 5 mV/m input 1000 kHzSelectivity at 1000 kHz a. 10 kHzinput = S/N 6 dB Sens. inputAGC Distortion at 1000 kH

5、z, 80% mod. 100 mV/m inputAGC Figure of MeritlF Rejection Ratio at 600 kHzlmage Rejection Ratio at 1400 kHzBandwidth at 6 dB downDistortion 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 Modula

6、tion of 2nd and 3rd harmonic, at 1 mV/m,5 mV/m and 100 mV/m inputDial Calibration at 600 kHzat 1400 kHzOverload: With a radiated signal of 1Ylm, the signal shallbreakup.FM BANDFrequency CoverageIFIHF Sensitivity at 90 MHzat 98 MHzat 106 MHzNew IHFS/N 50 dB Ouiting Sensitivity at 90, 98 and 106 MHzS/

7、N Ratio at l mV input3 dB Limiting SensitivitylF Rejection Ratio at 90 MHzlmage Rejection Ratio at 106 MHzSpurious Response and Cross ModulationCapture RatioAlternate Channel Selectivity 100 pV inputDistortion at 1 mV inputDial Calibration at 90 MHzAFC Holding Range at 1 mV inputTemperature Range fo

8、r Satisfactory operationAM SuppressionMaximum Signal Handling CapacityTape out Level at 1 mV input (RCA)Tape out Level at 1 mV input (DlN)UNITkHzkHzpV lmpV lmpY lmdBdBo/odBdBdBkHzo/omVmVHz%38kHz 0 r,25kHz 0 4.50tunable without undue distortion or32 254850 4235 2845 386 4.5-90.8 2200 200 *.2.5 dB15 1

9、5 r 2.5 dB50-2200 B0-1800NOMINAL510-165045520020020045LIMIT520-162050050050040beUNITMHzMHzpVpVpVdBfpVdBfdBpVdBdBdBdBdBo/okHzkHzCdBmVmVmVNOMINAL86.5-10910.71.91.91.910.82.814.2651.8855B801.5600.1a.250LIMIT88- 1 0B3.83.83.816.84.518.2553.57048654480.51 250t250 +. 1000-4542100750 .t. 2.5 dB15 a.2.5 dB5

10、020075015-3-Muting SensitivityF 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 BANDStereo I ndicator SensitivityStereo Separation at 1 mV inputStereo Distortion at l mV, 1 kHzPilot and Sub-carrie

11、r LeakageAUDIO SECTIONat 100 Hzat 1 kHzat 10 kHzinputlnput lmpedance PHONO MAG.AUXTAPE INOutput Power, TH D 0.5% from 20 Hz to 20 kHz,I ohms Both Channel DrivenOutput Power, THD 0.5% at 1 kHz Both Channel DrivenDistortion at 5 W from 20 Hz to 20 kHzSensitivity for Rated Power (22WPHONO MAG.AUXTAPE I

12、NFrequency Response at AUX from 20 Hz to 20 kHz input,1 W outputBass Action at 100 HzTreble Action at 10 kHzMin. Volume Hum & NoiseSignal 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 PositionLoudness contour ch. at

13、100 Hz -30 dB Vol. positionLoudness contour ch. at 10 kHz -30 dB Vol. positionChannel Balance at AUX, Vol. = Max.TAPE OUT Level PHONO MAG. (RCA)AUX, (RCA)PHONO MAG. Equalizer Response at 100 Hzat 10 kHzPHONO MAG. Over Load (THD = 0.5%)DC BalanceUNITpVdBdBdBNOMINAL5.5UNITpVdBdBdBo/odBUNITK ohmK ohmK

14、ohmNOMINAL5.53B48350.550NOMINAL50505025270.152.2160160F lata.10i.10165757555+9+4150150+ 13.1 1-13.751200LIMIT3.5-9.0*1ae_J*1 oa_J1l anLIMIT3.5-9.02833281.545LIMIT22240.32.2t3dB160f3dB160r3dB*-2a.10 L 2.5r_10 i.2.5355656545+9 i 2.5+4 r.2.5r-2150 r 3 dB150 i.3 dB*.2 dBr_2 dB90*.30WWo/omVmVmVdBdBdBmVdB

15、dBdBdBdBdBdBmVmVdBdBmVmV-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 roomtemperature is 25 degrees C.Nominal Specs represent t

16、he design specs; all units should be able to approximate these - some willexceed and some may drop slightly below these specs.Limit Specs represent the absolute worst condition which still might be considered acceptable; inno case should a unit perform to less than within any Limit Spec.2. DISASSEMB

17、LY INSTRUCTIONS1) To remove Chassis f rom wooden cabinet.Turn the cabinet upside down and re-move the six screws from the bottomcabinet. (Figure A)2) Removal of Front Panel.a) Remove the chassis from woodenb) Pull out the Main Chassis.c) Remove the two screws from the topd) Remove knobs and pull off

18、 panel.FigureAcabinet as described in 1).and three screws from the bottom of(F igure B1 , B2lthe Front Panel.3)To remove Rear Panel from chassis.Remove the four screws from the RearPanel. (F igure C)Figure B1Figure 82-5-aEUYUIIa.Iri-;- 1E59t!i-NIIO_.1auaEo=ooidooll93 e-d LF,E;-o?50 iij*i:33or;l -oEE

19、 i ooz!E;I=Pg66=N=E=oEE=EF3. BLOCK DIAGRAM-6-4. DIAL STRINGING DIAGRAM*START WITH CAPACITOR SET AT MINIMUM.PLATES FULLY OPEN (UNMESHED).*Pointer Position : HIGH END5. LEVEL DIAGRAMFIAUDIO FREQIJENCY. lkHz-7-6.ALIGNMENT INSTRUCTIONSAUDIO CIRCUIT ADJUSTMENT,/CHECKEOUIPMENT REOUIRED1. DC Voltmeter2. Au

20、dio Oscillator3. Oscilloscope4. AC VoltmeterNote: 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

21、 resistors, see P.C.B. view.(-25mV to+25mV)Figure 6Oscilloscoge (Shorled OutpuiCondition)(Normol Condiiion)Figure 5MAIN AMP ADJUSTMENTSTEPADJUSTMENTEOUIPMENT CONNECTIONAUDIO FBEO.LEVELADJUSTMENT1Check Balance bymeasuring DC voltageacross Output Termi-nal of L and R chan-nel.DC VoltMeterSee Figure 1N

22、o signalDC voltage shouldbe less than 25 mV2ldling current adjust-mentDC VoltMeterSee Figure 2.No signalAdjust so voltageacross Emitterresistors R633 ancR634 is 5 mV(8 ohm load).VR601VR602FigureCHECKING LIMITER CIRCUITSTEPADJUSTMENTEOUIPMENTCONNECTIONAUDIO FREOSETTINGLEVEL1Audio Osc.V.T.V.M.Oscillos

23、copeSee Figure 3.1000 HzVOLUME: Max.BASS, TREBLEBALANCE:centerAdjust input toAUX to get out-put level at justthe clipping point(4 ohm load)Figure 4.2Check the limiterci rcu i t.Audio Osc.V.T.V.M.OscilloscopeSee Figures 3,5.1000 HzSame as aboveCheck that outputdropt to a squarewave across R633(R634)

24、when out-put speaker termi-nals are shorted.See Figure 6.4ohm L.od,A-.-(yoc -+)AUDIO Osc. AUX SrA-79( rooHz)Figure 3Oscilloscope1J-8-AM RF & IF ALIGNMENTEOUIPMENT REOUIRED1. AM Signal Generator2. AC Voltmeter3. Oscilloscope4. Distortion MeterFigure 7Note: *Signal generator output should be no higher

25、 than necessary to obtain an output reading.*Maintain line voltage at 12O volts, 60 Hz AC (UL & CSA) (240 volts, 50 Hz AC for Australianmodels).Set SELECTOR Switch to AM.*See P.C.B. illustrations for alignment points/adjustments and Figure 7.osclLloscoPE DtsToRTloNAC VOLTMETER METERTAPE OUT(LorR)Fig

26、ure 8-9-16)lovl-)_,ff,r=-NE1203 tc20lzMl! 4 h,!iNltNl il E: t :/ Li ,t)lr2o2 r2o3 ;I ti6 6d De , - |6G_=_j r2orSTEPSIGNAL GENERATORCOUPLINGSIGNAL GENERATORFREOUENCYDIALSETTlNGINDICATORADJUSTMENTREMARKS1Connect standard loopANTENNA to SignalGenerator and radiatesignal into the AM Fer-rite Antenna.See

27、 Figure 8.455 kHz(400 H2,30% mod.)Point ofnon-inter-ference(near600 kHz)Scope and,AC Volt-meter toTAPE OUTJack.r202T203(AM IFT)Adjust for maxi-mum reading onmeter.2Same as STEP 1.510 kHz(400 H2,30% mod.)TuningGangfullyclosed.Same asSTEP 1.L2O3 (AM OSCCoil)Adjust for maxi-mum reading onmeter. Refer t

28、oFigures 7 and 8.3Same as STEP 11650 kHzl4OO H2,30% mod.)TuningGangfullyopened.Same asSTEP 1.TC105 (AMOSC Trimmer)Adjust for maxi-mum reading onmeter. Refer toFigures 7 and 8.4Same as STEP 1600 kHz(400 H2,30% mod.)600 kHzSame asSTEP 1.L8O2 (AM ANT.Coil)Adjust for maxi-mum reading onmeter. Refer toFi

29、gures 7 and 8.5Same as STEP 11400 kHz(400 Hz, 30% mod.)14OO kH,zSame asSTEP 1.TC104 (AMANT. Trimmer)Adjust for maxi-mum reading onmeter. Refer toFigures 7 and 8.6Repeat STEPs 4 and 5 until no further change is noticed.7Same as STEP 11000 kHz(400 kHz,30% mod.)Output level to100 mV/m1000 kHzAM SignalM

30、eter on Set.VR201Adjust so theMeter Pointeron Receiver isat about 85%of full scale.2 -_.4 AM BAR ANTENNA(6ocm) L/ l/_/ffiwflFM RF & IF ALIGNMENTEOUIPMENT REOUIRED1. FM Signal Generator2. AC Voltmeter3. Oscilloscope4. Distortion Meter5. CenterTuning Meter (1.2K ohm,200pA)Note: Signal Generator output

31、 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 Australianmodels).Set SELECTOR Switch to FM.Refer to P.C.B. illustration and Figure 7 for test points/adjustments.STEPGENERATORCOUPLINGGENERATORFREOUENCY

32、D!ALSETTINGINDICATORADJUSTMENTREMARKS1Signal Generator toFM Antenna Termi-nal thru FM DummyAntenna (300 ohm)98 MHz(400 Hz75 kHz dev.)lnput: about2-3 ttYNear98 MHzAC Voltmeter.Scope and Dis-tortion meterto TAPE OUTJack (L or R).T101Adjust for maximumreading on meter.Refer to Figure 1 1.2Same as STEP

33、198 MHz(400 Hz,75 kHz dev.)lnput: no input(unit off )Near98 MHzConnect theCenter TuningMeter (1.2 kO,200 pA) to PinNo.12(+)andNo.13(-)onAM/FM IFBoard (Referto Figures 7and 9A.)T201(Primary)Adjust for Centerpoint on Center Tu-ning Meter.Refer to Figures 9,9A, 10 and 1 1.3Same as STEP 198 MHz(4OO Hz,7

34、5 kHz dev.)lnput: 1 mVSame asSTEP 1.AC Voltmeter,Scope and Dis-tortion Meterto TAPE OUTJack (L or R).T201(Secondary)Adjust for minimumDistortion (about0.1%). Refer toFigure 9, 10 and 1 1.4Repeat STEPs 1 ,2 and 3 until no further improvement is noticed.5Same as STEP 1.90 MHz(40O Hz,75 kHz, dev.)lnput

35、: about2-3 ttY90 MHzSame asSTEP 1.L101 (FMAntenna Coil)1103 (FM RFCoil-stretch orsqueeze)Ll05 (FM OSCCoil)Adjust for maximumreading on meter.Refer to Figures 7and 1 1.bSame as STEP106 MHz(400 Hz,75 kHz dev.)lnput: about2-3 ttY106 MHzSame asSTEP 1.TC 101(FMAntenna Trim-mer)TC1O2 (FM RFTrimmer)TCl03 (

36、FM OSCTrimmer)Adjust for maximumreading on meter.Refer to Figures 7and 1 1.7Repeat STEPs 5 and 6 until no further improvement is noticed.8Same as STEP 198 MHz(400 Hz,75 kHz dev.)lnput: 5 trrV98 MHzSame asSTEP 1.VR2O3MUTE switchedON and adjustVR203 for no signaloutput.ISame as STEP 198 MHz(4OO Hz,75

37、kHz dev.)lnput: 100 mV98 MHzSignal Meteron Set.vR202Adjust so the MeterPointer on Receiver isabout 90% of full-scale.-10-T20tFigure 9PATTERNIF.iIcoRE TURNING DlREcTloN (clockvise-A-8. Re. Fiqure9)( r20l)Figure 1OCanter Tunlng Mder(l.2ko,2oOtA)Figure 9AFM EXTAntenno Terminol (3OOn)-11 -FM STEREO ALIG

38、NMENTEOUIPMENT REOUIRED1. Stereo Modulation Connect Stereo Modulator to EXT. Mod. terminal of FM SignalGenerator.Modulation Level of 19 kHz Pilot Signal . . .8-1Oo/o.2. FM Signal Generator . . Output Level - 1 mVFrequency - Approximately 98 MHzDeviation 75 kHz, 100% modulation of composite signal3.

39、Audio Generator4. AC Voltmeter5. Oscilloscope6. Distortion Meter7. Frequency CounterNote: See P.C.B. illustration for alignment/test points.PreliminariesSet SELECTOR Switch to FM STEREO and MUTE Switch to OFF position.MULTIPLEX & SEPARATION ALIGNMENTSTEPSIGNAL GENERATORCOUPLINGSTEREOMODULATIONINDICA

40、TORADJUSTMENTREMARKS1Connect to FM Antennaterminal thru FM dummyantenna (300 ohm).Mono. l kHz(1000 Hz, NoMod.)lnput: 1 mVCounter connectedto TP at Pin No. 12of lC2O2.VR2O5Adjust for 19 kHz1 50 Hz on Counter.Refer to Figure 12.2Same as above.Composite MPXSignal 1 kHz onLeft channelONLY.AC Voltmeter c

41、on-nector for TAPEOUT Jack of RightChannel.vR204(Separation )Adjust for minimumreading on meter.Refer to Figure 13.3Same as above.Composite MPXSignal 1 kHz onRight channelONLY.AC Voltmeter con-nector for TAPEOUT Jack of LeftChannel.Same as above.Same as above.4Repeat STEPs 2 and 3 until AC Voltmeter

42、 reading is at least -40 dB same channel output.(ie. 40 dB separation).5Same as STEP 1Composite MPXSignal 1 kHz.AC Voltmeter con-nected to TAPEOUT Jack.With 5.5 pV antenna in-put signal, Stereo indi-cator lamp should comeon.FM STEREO ALIGNMENT SET.UPANTENNAL(30On)t61514t3t2|totc202 LA 3350r/Q-3OOnFM

43、 EXT. AITERIVINAL(STA-7REO MODULATOR FM SIGNAL GEAC VTVMAIU99(q-)9?V99Tl-.-/Figure 12- 12-Figure 137. TROUBLESHOOTINGSYMPTOMCAUSE,/ REMEDY1 ) No output1) Faulty AC power cordReplace the cord.2) Defective POWER switchReplace the switch.3) Broken wire in the Power TransformerReplace the Transformer.4)

44、 Blown primary switchReplace the Fuse.2) Pilot Lamp does not light.1) Broken LampReplace the Lamp.2) Open in the Power Transformer tertiary windingReplace the Transformer.3) Pilot Lamp lights but no Speaker output.1 ) Defective capacitor C802 or 803Replace the defective capacitor(s).2) Defective Rec

45、tifier D703Replace the defective Rectifier.3) Defect in the Power Transformer secondary windingReplace the Power Transformer.4) Blows Fuse1) Defective Rectifier D703Replace the defective Rectifier.2) Short-circuit in the rectifier circuitRemove the short.3) Short-circuit in Power Transistor CircLitr

46、y TR611-614Repair circuit and/or replace the defective Transistor(s).5l A Speakers does not work.1) Speaker Selector Switch defectiveReplace the switch.2l Poor contact in Speaker Output TerminalsReplace or repair it.3) Poor contact in Speaker Selector SwitchRepair or replace it.6) B Speakers does no

47、t work.1) Speaker Selector Switch defectiveReplace the switch.2) Poor contact in Speaker Selector SwitchRepair or replace it.3) Poor contact in Speaker Output TerminalsRepair or replace it.7) No output one channel with VOLUMEat maximum and BALANCE at center,when a test signal is applied to thetermin

48、al of non-operating channel of theBALANCE control VR502.1) Defective Transistor TR501-503 or TR601-618Replace the defective Transistor(s).2) Defective resistor or capacitor of TONE and MAIN AMP circuitReplace the defective part(s).8) No output when a test signal is applied tothe input terminals, exc

49、ept PHONO input.1) Defective MONO-Stereo or TAPE MONitor SwitchRepair or replace the Switch.2) Defective SELECTOR SwitchReplace the Switch.9) No output when a test signal is applied tothe PHONO input terminals.1) Defective transistor, resistor or capacitor of PRE EO AMP circuitReplace the part(s).2)

50、 Defective MONO-Stereo or TAPE switchRepair or replace the switch.3) Defective SELECTOR SwitchReplace the SELECTOR Switch.-13-SYMPTOMCAUSE ,REMEDY10) Speaker works normally but Headphonedoes not work.Defective R647 (Left) or R648 (Right)Change it.Headphone plug does not mate with jackReplace the plu