Realistic-STA720-rec-sm 维修电路原理图.pdf

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1、ruLtstd.SerulceamuaIAM/FMSTA-720STEREOREGEIVERCatalog Number: 31-1997LDcusloM MANUFACTURED FoR RADIo sHACKn ovstoN 0F TANDv coRpoRATtoNRadioFans.CN 收音机爱 好者资料库CONTENTS1. SPECIFICATIONS .3&42, BLOCK DIAGRAM. .53. DISASSEMBLYINSTRUCTIONS. .64. DIAL STRINGING DIAGRAM .65. ALIGNMENT PROCEDURES .7 _96. AL

2、IGNMENT POINTS. . .107. LEVELDIAGRAM. .118. TROUBLESHOOTING. 12_169. 0074 TUNER BOARD. . . 17 & 1810. 6079 MAIN AMP BOARD 19 & 2011. 7225 FREOUENCY COUNTER BOARD ., , . ,. ,.21 L/12. 7226 SWTTCH BOARD .2213. 8044 POWER SUPPLY BOARD , ,. , ,., .232414. 9046 TONE CONTROL BOARD . ! ! r. ! !/15. SEMICON

3、DUCTOR LEAD IDENTIFICATIONS . .,.,.2516. ELECTRTCAL PARTS LIST . 26- 3317. lC EOUIVALENT CIRCUIT .3418. MTSCELLANEOUSPARTSLTST. .3519. SCHEMATIC DIAGRAM. . SEPARATE SHEETIlII20, EXPLODED VIEW. . SEPARATE SHEET :+eRadioFans.CN 收音机爱 好者资料库SPECIFICATIONSNOMI NALLIMITUN ITFM1.2.SECTIONTUNING COVERAGEDIAL

4、 CALIBRATION ACCURACY 90 MHz98 MHz106 MHzUSABLE SENSITIVITY(NOTSE & DTSTORTTON -30 dB)IMAGE REJECTION (at 106 MHz)lF REJECTION (at 90 MHz)FULL LIMITING (at -3 dB)lF BANDWIDTH (6 dB down)DISTORTION (1 mV INPUT)SIGNAL-TO-NOISE RATIO (1 mV INPUT)DE-EMPHASIS (at 50-10000 Hz)DISCRIMINATOR BANDWIDTH (Peak

5、-to-Peak)AFC HOLDING RANGE (witfr 1 mV signal)OUTPUT VOLTAGE MONO(at 75 kHz dev., 4OOHz mod., 1 mV input) STEREOMUTING THRESHOLDOVERLOAD (THD at 98 MHz, 100% mod.)100 mV RF INPUTSPURIOUS RESPONSE at 98 MHzANTENNA INPUT 3 pV, 112lF, 103.35 MHzCAPTURE RATIO (1 mV INPUT)ALTE RNATE CHANNE L SE LECTIVITY

6、(100 pV INPUT)50 dB OUIETING SENSITIVITY at 98 MHz3.4.5.6.7.8.9.10.11.12.13.14.15.16.17.18.19.RadiatedTerminalMPX SECTION1, STEREO SEPARATION(100% mod., 1 mV input)100 Hz1 kHz10 kHz2, DISTORTION(1OOY mod., 1 mV input) 1 kHz3. STEREO BEACON SENSITIVITY (pilot 7%)4. RESIDUAL 19 kHz & 38 kHz (1 mV inpu

7、t)5. SUPPRESSION OF SCA INTERFERENCE(1 mV input)AM SECTION1. TUNING COVERAGE2. DIAL CALIBRATION ACCURACY 600 kHz1,000 kHz1,400 kHz3. USABLE SENSITIVITY(400 H2,30% mod.,600 kH2,1000 kHz, 1400 kHznoise & distortion -20 dB)4. IMAGE REJECTION (at 1,400 kHz)5. lF REJECTION (at 600 kHz)6. AGC FIGURE OF ME

8、RIT(from 100 mV/m at 1,000 kHz)7. DISTORTION(400 H2,30% mod., 5 mV/m input)8. lF BANDWIDTH (6 dB down)87.4-109*tb0t50t501.79.855801.20.1570t 1.5400t12OO0.75o.760.3801.0553.016.14045380.3840510-1660320254835400.8BB_1OBt 100t 100t 1002.412.850701.8t 1500.565t2300tB000.75t3 dB0.7t3 dB4-100.8702.5452832

9、250.86.020.85-123040520-1620t15t20t402.06-1460040402835MHzkHzkHzkHzpVdBfdBdBpVkHzo/odBdBkHzkHzVpVo/odBdBdBdBo/okHzkHzkHzkHzpY lmpVdBdBdBo/okHzdBdBpVdBfpVdBdB-.,NOMINALLIMITUN IT9. OUTPUT VOLTAGE(1 kHz 30% mod., 5 mV/m input)10. AUDIO RESPONSE(5 mV/m input from 50 Hz to 2.3 kHz, 0 dB 1,000 kHz)11. SE

10、LECTIVITY 200 pVlm12, SIGNAL-TO-NOISE RATIO(1,000 kl-2, with antenna input 10 mV/m)13. AM BEAT 1 - 50 mV/m50 - 100 mV/mAUDIO SECTION1. RMS OUTPUT POWER(distortion ?o.y oF=Jr1_-ittt. l-t t=t!lE 6:6 Ed HdNNVH! TB!IU5EtrFaADISASSEMBLY INSTRUCTIONS1. Removing chassis from metal enclosure.Remove five scr

11、ews (#63 & #41lr from sides and back.2. Removing the Front PanelPull off all of the control knobs except for push buttons.Remove six screws (#35) from top and bottom of the Front Panel,then remove the Front Panel.(Refer to Miscellaneous Parts List for descriptions of numbered parts.)DIAL STRINGING D

12、IAGRAMNote: Tuning capacitor should be in fully closed position.fi-rl2 TURNS)6ALIGNMENT PROCEDURESDo not attempt alignment unless the following equipment is available.1. AM Signal Generator2. Oscilloscope3. AC Voltmeter4. FM Signal Generator5. Stereo Modulator6. Audio Generator7. Distortion meter8.

13、DC Voltmeter9. Frequency Counterwhen aligning.Note: Remove line cord antenna from FM external antenna terminalAM IF & RFALIGNMENTNote: Remove line cord antenna from FM external antenna terminal when aligning.RECEIVERLoop AntennaFis. 1 AM ALIGNMENT CONNECTIONTAPE OUTOutput of signal generator should

14、be no higher than necessary to obtain an output reading.Signal Generator Modulation: 30%Set SELECTOR switch to AM.STEPSIGNALGENERATORCOUPLINGSIGNALGENERATORFR EOUENCYRECEIVERDIALSETTINGINDICATORADJUSTMENTRefer Fig. 4.REMARKS1Refer Fig. 1455 kHz(400 Hz Mod.)Point of non-interference(on/about600 kHz)A

15、C Voltmeterto TAPE OUTjack1401 ilFT)Adjust for maxi-mum reading.2Same as Step 1600 kHz(400 Hz Mod.)600 kHzSame as Step 1L401 (OSC Coil)L451 (ANT Coil)Same as Step 13Same as Step 11400 kHz(400 Hz Mod.)1400 kHzSame as Step 1TC402(OSC Trimmer)TC4O1(ANT Trimmer)Same as Step 1TUNERFRONT ENDTC401,TC402L40

16、1FM RF AND IF ALIGNMENTFor European model, the lowest frequency of FM tuning range should not be below 87.5 MHz.FM Dummy Antenna to 300 S2 antenna terminal of ReceiverZin = 50 o (75 o)Zout=3OOO (balanced)Signal generator output should be no higher than necessary to obtain an output reading.Set Selec

17、tor switch to FM.Signal Generator deviation: 75kHz NOTE: Be sure to disconnect FM line cord antenna during alignment.STEPSIGNALGENERATOBCOUPLI NGSIGNALGENERATORFR EOUENCYR ECE IVERDIALSETTI NGINDICATORADJUSTMENTRefer Fig. 4.R EMARKS|Connect to FMAntenna Termi-nal thrbughFM DummyAntenna(300 O) Fis. 2

18、90 MHz(400 Hz Mod.)90 MHzAC Voltmeterconnected toTAPE OUTjackL1 01(ANT. COIL)L102(RF COIL)L1 04(OSC. COIL)Adjust for maxi-mum reading onAC Voltmeter.2Same as Step 1106 MHz(400 Hz Mod.)106 MHzSame as Step 1TClO1(ANT. Trimmer)TC1 02(RF Trimmer)TC103(OSC. Trimmer)Same as Step 1Repeat steps 1 & 2 until

19、no further improvement is possible.3Same as Step 190 MHz(400 Hz Mod.)90 MHzSame as Step 1T101 flFT)Same as Step 14Same as Step 198 MHz(400 Hz Mod.)98 MHzDC Voltmeterconnected to Pin#31 and TP onPCB #OO74AT201Adjust tor zeroreading on DCVoltmeter.5Same as Step 198 MHz(400 Hz Mod.)98 MHzDistortion Met

20、erconnected toTAPE OUTjackT202Adjust for mini-mum distortion.6Same as Step I98 MHz(400 Hz Mod.)98 MHzSIGNALSTRENGTHlndicator LEDVR201Adjust for FullSignal lndicationwith input of500 pV7Same as Step 1(Set Selectorswitch to FMMUTE.)98 MHz(400 Hz Mod.)98 MHzSame as Step 1vR202Adjust for zeroreading on

21、ACVoltmeter withSG output levelof 6 ptV12s a (112.5 s,)150 r,Fig,2 FM DUMMY ANTENNAMPX ALIGNMENTFM ANTENNATERMINAL(300 a)MAIN AMPLIFIER ALIGNMENTTAPE OUTPin #46TUNERFRONT ENDL101, L102, Ll04T201 , TC1 01TC102. TC103FM SIGNALGENE RATORFM DUMMYANTENNA300 C,FM IFVR201vR202MPXVR3O1VR3O2STE BEOMODULATORF

22、is.3 FM RF, lF AND MPX ALIGNMENT CONNECTIONSet SELECTOR Switch to FM.Tune for 98 MHz on band.Signal Generator output level: 1000pV Deviation: 75 kHz at 100% modulation of composite signalConnect Sigpal Generator to FM Antenna Terminal through FM Dummy Antenna (300 S).STEP19 kHz(PILOT SIGNAL)MODULATI

23、ONLevelSIGNALGENERATORFreq. Set toOUTPUTINDICATORConnected toADJUSTReferFig. 4ADJUSTFORNOTEFrequency counterconnected to Pin#46 and GroundVR30119 kHz28o/Composite 1 kHzR channelAC Voltmeterconnected toTAPE OUT jackof R channelAdjust inputfor Audio out-put of about0.7 v.38o/oComposite 1 kHzL channelA

24、C Voltmeterconnected toTAPE OUT jackof R channelVR3O2minimumAC Voltmeterreading shouldbe at least 32dB below read-ing in step 2.48o/oComposite i kHzR channelAC Voltmeterconnected toTAPE OUT jackof L channelVR302mrntmumsame as Step 3lf you did not obtain -32 dB readings in steps 3 and 4 (compared wit

25、h step 2), readjust VR302 until you obtain -32 dBreading for both steps 3 and 4.INDICATORADJUSTMENTREMARKSDC VoltmeterV R601a,bAdjust for 0.005 - 0.015 voltsacross R619 a, b with no signal.ALIGNMENT POINTSVR601a R619a#3lPrNL45lTl 01Ll 04102Lt0lTCl 03TCl02TCI(1TC40tTC402T4011401vR202TPVR20lr201T202V

26、R3O2#46 PtNVR3(1$ls &:,*-wailFis.4vR60lb R619b10LEVEL DIAGRAMFREOUENCY - lkHzSPEAK E ROUTm!60.gza50oLrJOiiFoVO LUMEI NPUTSELECTO 8l4.l4v25W /8s211TROUBLESHOOTINGSYMPTOMCAUSE AND REMEDYReceiver not operative; functionindicator des not light.A) Faulty AC power cordReplace the cord.B) Defect in the pow

27、er switchReplace the switch.C) Broken wire in the power transformerR ep lace the transformer.D) Blown power fuse F002Replace the fuse.2. Fr.rse blows when power is turned on.A) Power transformer T851 defectiveReplace the transformer.B) Short in the primary or secondary of the transformercircuitryRep

28、air the short.C) Damaged rectifier D801Replace the rectifier.D) Short circuit in the rectif ier circuitRepair the short.3. Function indicator lights but nosound from both channels.A) SPEAKERS switch 510 or 511 defectiveReplace the defective switch(es).B) Defebt in transistors TR605a,b - TR60Ba,b ofM

29、ain Amp Board #6079Replace the defective transistor(s).4. A speakers do not work.A) Speaker switch S10 defectiveReplace the switch.5. B speakers do not work.A) Speaker switch S11 defectiveReplace the switch.6. One channel does not work withVOLUME at maximum with a testsignal applied to the center te

30、rminalof VOLUME control VR902 of thedead channel.A) Defective 1C901Replace 1C901 .B) Defect in transistbr TR601-TR610 of Main AmpBoard #6079Locate and correct the defect.C) Break in copper foil of printed circuit board#9046 or #6079Repair or replace circuit board(s).D) Short in speaker output termin

31、alRepair the short.E) Defective resistor R901, R601, R603-R610,R615-R620Replace the defective resistor(s).F) Defective capacitor C901, C601, C603 or C604Replace the defective capacitor(s).12SYMPTOMCAUSE AND REMEDY7. Same as (6) above but channeloperates when test signal is appliedas in (6).A) Defect

32、ive PHONO switch 52 or TAPE MON switchS7Repair or replace the switch(es).B) Defective BALANCE control VR901Replace.C) Resistor R910 defectiveReplace the resistor.B. Speaker works normally butheadphone do not work.A) Headphone plug does not mate with jack.Replace the plug.B) Defective resistor R651a,

33、bReplace the resistor(s).9. All inputs work normally exceptfor AUX input.A) Poor contact in AUX input jackRepair or replace the jack.B) Faulty AUX switch S1Repair or replace the switch.C) Defective resistor R510Replace the resistor.10. PHONO input not operativeA) Defective 1C501Replace the lC.B) Fau

34、lty resistor R501, R503-R509Replace the faulty resistor(s).C) Fau lty capacitor C501 -C503Replace the faulty capacitor(s).D) Poor contact in PHONO input jackRepair or replace the jack.E) Faulty PHONO switch 52Repair or replace the switch.11. TAPE MON not operativeDefective TAPE MON switch 57Repair o

35、r replace the switch.Defective contact in TAPE lN jack(s)Repair or replace the jack(s).A)B)12. FM does not operate.A) Short circuit in Tuner B+ circuitRepair the short.B) Defective FM(S4) or FM MUTE(S5) switchRepair or replace the switch(es).C) Resistor R219, R306, R317 or R318 defectiveReplace the

36、defective resistor(s).D) Choke coil L201 defectiveReplace the coil.E) Capacitor C302 defectiveReplace the capacitor.F) Defective lC 1C201 or 1C301Replace the defective lC(s).G) Defective I FT T101Replace lFT.13SYMPTOMCAUSE AND REMEDYH) DefectivetransistorTRl0l, TR102, TR103 orcoil L101, L104Replace

37、the defective component(s).l) Faulty lead-inRepair the faulty lead-in.13. Poor multiplex separationA) lmproper adjustmentReadjust VR302 (refer to ALIGNMENTPROCEDURE on page g).B) Transistor TR302, TR303 or lC 1C301 of TunerBoard #OO74 defectiveReplace the defective component(s).C) Variable resistor

38、VR301 or VR302 defectiveReplace the defective variable resistor(s).14. Stereo indicator does not light.A) Defective indicator LED D406Replace the LED.B) lmproper adjustment of VR301 of Tuner Board#0o74Make readjustment.(Refer to MPX ALIGNMENT on page 9.)C) Defective lC 1C301 or resistor R426Replace

39、the defective component(s).15. FM volume not sufficientA) lf volume of both L and R channels not enough:Front-End section defective, or faulty IFT T101lC 1C201 or transistor TR201 of Tuner Board#0074Locate and replace the defective component(s).B) lf sound of one channel not enough: DefectiveTR302 i

40、n case of L channel, or defective TR303in case of R channelReplace the defective transistor.16. AM does not operateA) Damaged 1C401 of Tuner Board #0074Replace the lC.Defective L4O1,T4O1,T4O2 or CF401Replace the defective component(s).One of resistors of Tuner Board #0074 (AMsection) defectiveReplac

41、e the defective resistor.One of capacitors of Tuner Board #0074 (AMsection) defectiveReplace the defective capacitor.AM switch 53 defectiveRepair or replace the switch.Defective Tuning gang capacitorRepair or replace.Damaged AM Bar antennaRepair or replace bar antenna.B)c)D)E)F)G)14SYMPTOMCAUSE AND

42、REMEDY17 . LOUDN ESS has no effect.A) Defective LOUDNESS switch 59Replace the switch.B) Defective capacitor C91 1, C912 or resistor R91 1Replace the defective component(s).C) Defective VOLUME control VR902Replace.18. Stereo-Mono not effectiveA) Defective MONO switch 58Replace the switch.19. TAPE MON

43、itor not effectiveA) Defective TAPE MON switch 57Replace the switch.B) Poor contact in TAPE MON lN jacksRepair or replace the jack(s).20. BASS control has no effect.A)B)BASS control VR903 defectiveReplace.Defective capacitor C903, C904 or resistorR915, R917Replace the defective component(s).21. TREB

44、LE control has no effect.A) TREBLE control VR904 defectiveReplace.B) Defective capacitor C905-C907 or resistorR918, R919Replace the defective component(s).22. Excessive noise with PHONO inputA) Faulty 1C501Replace the lC.B) Faulty R501-R504, C501 or C506Replace the faulty component(s).23. Noisy VOLU

45、ME controlA) Defective VOLUME control VR902Replace the variable resitor.B) Defective capacitor C503, C901, C908 or C601R ep lace the defective capacitor( s).24. SIGNAL STRENGTH indicatorLED not functioningA) Defective LED D401-D405 or lC4O2Replace the defective component(s).B) ln case of FM receptio

46、n, VR201 or D2O2defectiveReplace the defective component(s).C) ln case of AM reception, 1C401 or R416 defectiveReplace the defective component(s).25. AUTO-Magic AFC has no effectwhen AUTO-M switch is ON.A) Defective D 101, R 1 18, R22O or C213Replace the defective component(s).15SYMPTOMCAUSE AND REM

47、EDY26. Frequency counter LED does notlight when FM or FM MUTE buttonis pressed in.A) Diode D803 defectiveReplace the diode.B) Capacitor C701, C704, C810Replace the defective capacitor(s).27. Frequency counter misreads in AMor FM reception.A) Defective crystal XR701Replace the crystal.B) Defective lC

48、 1C701 or transistor TR702-TR705Replace the defective component(s).28. Frequency counter misreads in onlyAM reception.A) Defective AM switch 53Replace the switch.NOTES1. This Receiver have two built-in over load thermal protection for abnormaloperation. When the temper-ature of thermal protector one

49、 is installed with heat sink (S14, 105C) and the other with powertransformer (S13, 90C) does rise abnormally (105 t 5C or 90 + 5oC), the thermal protector willautomatically cut out, and as soon as the temperature goes down sufficiently (35 t t5C), the ther.malprotector turns back-on automatical ly.l

50、f the Receiver does turn itself off, check ventilation and speaker connections.HEAT SINK Ft)R POWERPOWER TRANSISTORS TRANSFOEIVIEB2. Transistors TR609 and TR610 protect audio output stage when abnormally high current flows inTR607 and TR608 due to excessive input drive, or a too low impedance load c