欢迎来到收音机爱好者资料库! | 帮助中心 忘不了收音机那份情怀!
收音机爱好者资料库
全部分类
  • 德国收音机>
  • 国产收音机>
  • 日本收音机>
  • 国外收音机>
  • 进口随身听>
  • 卡座/开盘/组合/收录机>
  • CD/VCD/DVD/MD/DAC>
  • DAT/LP唱机>
  • 功放/音响/收扩>
  • 老电视>
  • ImageVerifierCode 换一换

    Aiwa-NSXSZ200-cs-sm维修电路原理图.pdf

    • 资源ID:158574       资源大小:6MB        全文页数:44页
    • 资源格式: PDF        下载积分:22积分
    会员登录下载
    三方登录下载: QQ登录
    账号:
    密码:
    验证码:   换一换
      忘记密码?
        
    友情提示
    2、PDF文件下载后,可能会被浏览器默认打开,此种情况可以点击浏览器菜单,保存网页到桌面,就可以正常下载了。
    3、本站不支持迅雷下载,请使用电脑自带的IE浏览器,或者360浏览器、谷歌浏览器下载即可。
    4、本站资源下载后的文档和图纸-无水印,预览文档经过压缩,下载后原文更清晰。
    5、试题试卷类文档,如果标题没有明确说明有答案则都视为没有答案,请知晓。

    Aiwa-NSXSZ200-cs-sm维修电路原理图.pdf

    SERVICE MANUALDATANSX-AJ200NSX-AJ205NSX-SZ200NSX-SZ205UUEZ,LHEZCOMPACT DISC STEREO SYSTEMS/M Code No. 09-012-440-9R1REVISIONBASIC CD MECHANISM : BZG-2 ZD4NCBASIC TAPE MECHANISM: ZZM-3 YPR2NCNSXAJ200(TYPE: U)SPEAKERSYSTEMSXNAJ202CXNAJ200REMOTECONTROLLERRCAAS11(VS)CDCASSEIVERNSXAJ205(TYPE: U)SXNAJ205SX-R145CXNAJ205NSXSZ200(TYPE: EZ)SXNSZ202CXNSZ200NSXSZ205(TYPE: EZ)SXNSZ205CXNSZ205NSXSZ200(TYPE: LH)SXNSZ205CXNSZ200 This Service Manual is the “Revision Publishing” and replace “Simple Manual” NSX-AJ200/AJ205/SZ200/SZ205, (S/M Code No. 09-011-440-9T1). If requiring information about the CD mechanism, see Service Manual of BZG-2 (S/M Code No. 09-00C-353-2N2).RadioFans.CN 收音机爱 好者资料库 2 SPECIFICATIONSTUNERFM tuning range:87.5 MHz to 108 MHzFM usable Sensitivity(IHF):13.2 dBf, 16.8 dBfFM antenna terminals:75 ohms (unbalanced)AM tuning range: 530 kHz to 1710 kHz (10 kHz step)531 kHz to 1602 kHz (9 kHz step)AM usablesensitivity:350 ?V/mAM antenna:Loop antennaMW tuning range:531 kHz to 1602 kHz (9 kHz step)530 kHz to 1710 kHz (10 kHz step)MW usable sensitivity:350 ?V/mLW tuning range:144 kHz to 290 kHzLW usable sensitivity:1400?V/mMW/LW antenna:Loop antennaAMPLIFIERCX-NAJ200Power output:20 W + 20 W (50 Hz - 20 kHz, THDless than 1%, 6 ohms)25 W + 25 W (1 kHz, THD less than10%, 6 ohms)Totalharmonic distortion:0.1% (10 W, 1 kHz, 6 ohms, DIN AUDIO)CX-NAJ205Power output:40 W + 40 W (50 Hz - 20 kHz, THDless than 1%, 6 ohms)50 W + 50 W (1 kHz, THD less than10%, 6 ohms)Totalharmonic distortion:0.1% (20 W, 1 kHz, 6 ohms, DIN AUDIO)CX-NSZ200 / CX-NSZ205Power output:12 W + 12 W (6 ohms, T.H.D.1%, 1 kHz/DIN 45500)Reference: 15 W + 15 W (6 ohms, T.H.D.10%, 1 kHz/DIN 45324)DIN MUSIC POWER: 39 W + 39 WTotalharmonic distortion:0.1% (6 W, 1 kHz, 6 ohms, DIN AUDIO)CX-NSZ200Power output:Rated: 40 W + 40 W (6 ohms, T.H.D.1%, 1 kHz)Reference: 50 W + 50 W (6 ohms, T.H.D.10%, 1 kHz)Totalharmonic distortion:0.1% (20 W, 1 kHz, 6 ohms, DIN AUDIO)Input:VIDEO/AUX: 500 mVOutput:SPEAKERS: 6 ohms or moreSURROUND SPEAKERS (only forCX-NAJ205): 8 ohms to 16 ohmsPHONES: 32 ohms or moreCASSETTE DECKTrack format:4 tracks, 2 channels stereoFrequency response:50 Hz - 8 kHzRecording system:AC biasHeads:DECK 1: playback x 1DECK 2: recording/playback x 1,erase x 1CD PLAYERLaser:Semiconductor laser (?= 780 nm)D/A converter:1 bit dualSignal-to-noise ratio:85 dB (1 kHz, 0 dB)Harmonic distortion:0.05 % (1 kHz, 0 dB)FRONT SPEAKERS SX-NAJ202 ( only for NSX-AJ200)Speaker system:2 way, bass reflex (magnetic shielded)Speaker units:Woofer: 120 mm (43/4 in.) coneTweeter: 20 mm (13/16 in.) coneImpedance:6 ohmsDimensions (W x H x D): 220 x 324 x 198 mm( 83/4 x 127/8 x 77/8 in.)Weight:2.3 kg (5 lbs 1 oz)FRONT SPEAKERS SX-NAJ205 ( only for NSX-AJ205)Speaker system:3 way, bass reflex (magnetic shielded)Speaker units:Woofer: 120 mm (43/4 in.) coneTweeter: 60 mm (23/8 in.) coneSuper tweeter: 20 mm (13/16 in.)ceramicImpedance:6 ohmsDimensions (W x H x D): 220 x 324 x 198 mm( 83/4 x 127/8 x 77/8 in.)Weight:2.5 kg (5 lbs 8 oz)FRONT SPEAKERS SX-NSZ202 ( only for NSX-SZ200)Speaker system:2 way, bass reflex (magnetic shielded)Speaker units:Woofer: 120 mm coneTweeter: 20 mm ceramic coneImpedance:6 ohmsDimensions (W x H x D): 220 x 324 x 198 mmWeight:2.3 kg (5 lbs 1 oz)FRONT SPEAKERS SX-NSZ205 (for NSX-SZ200, NSX-SZ205)Speaker system:3 way, bass reflex (magnetic shielded)Speaker units:Woofer: 120 mm coneTweeter: 60 mm coneSuper tweeter: 20 mm ceramicImpedance:6 ohmsDimensions (W x H x D): 220 x 324 x 198 mmWeight:2.5 kg (5 lbs 8 oz)SURROUND SPEAKERS SX-R145 (only for NSX-AJ205)Speaker system:1 way, bass reflexSpeaker units:Full range: 80 mm(31/4 in.) coneImpedance:8 ohmsDimensions (W x H x D): 100 x 132 x 116 mm(4 x 51/4 x 45/8 in.)Weight:0.5 kg (1 lbs 2 oz)Accessories:Wall mounting screws (2)GENERALPowerrequirements:120 V AC, 60 Hz230 V AC, 50 Hz120 V/220 - 230 V/240 V AC(Switchable), 50 Hz/60HzPower consumption:60 W, 67W, 53 W70 W,Power consumptionin standby mode:With ECO mode on: 0.6 WWith ECO mode off: 15 WDimensions ( W x H x D): 260 x 323 x 291 mm(101/4 x 123/4 x 111/2 in.)Weight:5.9 kg (13 lbs), 4.9 kg Design and specifications are subject to change without notice.RadioFans.CN 收音机爱 好者资料库This set employs laser. Therefore, be sure to follow carefullythe instructions below when servicing.WARNING!WHEN SERVICING, DO NOT APPROACH THE LASEREXIT WITH THE EYE TOO CLOSELY. IN CASE IT ISNECESSARY TO CONFIRM LASER BEAM EMISSION.BE SURE TO OBSERVE FROM A DISTANCE OF MORETHAN 30cm FROM THE SURFACE OF THE OBJECTIVELENS ON THE OPTICAL PICK-UP BLOCK.Caution: Invisible laser radiation whenopen and interlocks defeated avoidexposure to beam.sAdvarsel: Usynlig laserstling ved bning,nr sikkerhedsafbrydere er ude af funktion.Undg udsttelse for strling.VAROITUS!Laiteen Kyttminen muulla kuin tss kyttohjeessamainitulla tavalla saataa altistaa kyt-tjnturvallisuusluokan 1 ylittvlle nkymttmllelasersteilylle.VARNING!Om apparaten anvnds p annat stt n vad somspecificeras i denna bruksanvising, kan anvndarenutsttas fr osynling laserstrlning, som verskridergrnsen fr laserklass 1.CLASS 1LASER PRODUCTKLASSE 1LASER PRODUKTLUOKAN 1LASER LAITEKLASS 1LASER APPARATPROTECTION OF EYES FROM LASER BEAM DURING SERVICINGCAUTIONUse of controls or adjustments or performance of proce-dures other than those specified herin may result inhazardous radiation exposure.ATTENTIONLutillisation de commandes, rglages ou procduresautres que ceux spcifis peut entraner une dangereuseexposition aux radiations.ADVARSELUsynlig laserstling ved bning, nr sikkerhedsafbrydereerude af funktion. Undg udsttelse for strling.This Compact Disc player is classified as a CLASS 1LASER product.The CLASS 1 LASER PRODUCT label is located on therear exterior.Precaution to replace Optical block(KSS-213F)Body or clothes electrostatic potential couldruin laser diode in the optical block. Be sureground body and workbench, and use care theclothes do not touch the diode.1) After the connection, remove solder shown inright figure.PICK-UP ASSY PWB 3 SolderRadioFans.CN 收音机爱 好者资料库NOTE ON BEFORE STARTING REPAIRCharging voltage (V)Discharging Rated power (W)Parts number(C101, 102)resistor ()25-48100387-A00-247-09049-140220587-A00-232-090Note: The reference numbers (C101, C102) of the electrolytic capacitors can change depending on the models. Be sure to check thereference numbers of the charging capacitors on schematic diagram before starting the discharging work.2. Check items before exchanging the MICROCOMPUTERBe sure to check the following items before exchanging the MICROCOMPUTER. Exchange the MICROCOMPUTER after confirmingthat the MICROCOMPUTER is surely defective.2-1. Regarding the HOLD terminal of the MICROCOMPUTERWhen the HOLD terminal (INPUT) of the MICROCOMPUTER is “H”, the MICROCOMPUTER is judged to be operating correctly.When this terminal is “L”, the main power cannot be turned on. Therefore, be sure to check the terminal voltage of the HOLDterminal before exchange.When the MICROCOMPUTER is not defective, the HOLD terminal can also go “L” when the POWER AMPLIFIER has anyabnormalities that triggers the abnormality detection circuit on the MAIN C. B. that sets the HOLD terminal to “L”.Good or no good judgement of the MICROCOMPUTER11111Turn on the AC main power.22222Confirm that the main power is turned on and the HOLD terminal of the MICROCOMPUTER keeps the “H” level or not.33333When the HOLD terminal is “L” level, the abnormality detection circuit is judged to be working correctly and theMICROCOMPUTER is judged to be good.1. Forced discharge of electrolytic capacitor of power supply blockWhen repair is going to be attempted in the set that uses relay circuit in the power supply block, electric potential is kept charged acrossthe electrolytic capacitors (C101, 102) even though AC power cord is removed. If repair is attempted in this condition, secondary defectcan occur.In order to prevent the secondary trouble, perform the following measures before starting repair work.Discharge procedure11111Remove the AC power cord.22222Connect a discharging resistor at an end of lead wire thathas clips at both ends. Connect the other end of the leadwire to metal chassis.33333Contact the other end of the discharging resistor to thepositive (+) side (+VH) of C101. (For two seconds)44444Contact the same end of the discharging resistor as step33333 to the negative (-) side (-VH) of C102 in the same way.(For two seconds)55555Check that voltage across C101 and C102 has decreasedto 1 V or less using a multimeter or an oscilloscope.Select a discharging resistor referring to the following table.Fig-1MAIN C.BD101C101C1022234 4 RadioFans.CN 收音机爱 好者资料库In such a case, check also if the POWER AMPLIFIER circuit or power supply circuit has any abnormalities or not.2-2. Regarding resetThere are cases that the machine does not work correctly because the MICROCOMPUTER is not reset even though the AC powercord is re-inserted, or the software reset (pressing the STOP key + POWER key) is performed.When the above described phenomenon occurs, it can lead to wrong judgement as if the MICROCOMPUTER is defective and toexchange the MICROCOMPUTER. In such a case, perform the forced-reset by the following procedure and check good or nogood of the MICROCOMPUTER.11111Remove the AC power cord.22222Short both ends of the electrolytic capacitor C113 that is connected to VDD of the MICROCOMPUTER with tweezers.33333Connect the AC power cord again. If the MICROCOMPUTER returns to the normal operation, the MICROCOMPUTER isgood.Note: The reference number or MICROCOMPUTER pin number of transistor (Q110) and electrolytic capacitor (C113) can change dependingon the models. Be sure to check the reference numbers on schematic diagram before starting the discharging work.2-3. Confirmation of soldering state of MICROCOMPUTERCheck the soldering state of the MICROCOMPUTER in addition to the above described procedures. Be sure to exchange theMICROCOMPUTER after surely confirming that the trouble is not caused by poor soldering but the MICROCOMPUTER itself.Fig-2-2MICRO-COMPUTERMICROCOMPUTERFRONT C.BFRONT C.BVSSVDDC113*%C1131815Short with tweezers. 5 RadioFans.CN 收音机爱 好者资料库KANRINO.REF. NO.DESCRIPTIONPART NO.KANRINO.REF. NO.DESCRIPTIONPART NO.ELECTRICAL MAIN PARTS LIST 6 ? !? !?#?$? !?%?$?$?&%?%?$?%?$?(?)?%?*?%?%?$?%?$?%?*%?$?%?%?$? ? ?!?%?$?#!?%?$?!?%?$? ? ?!?%?$?#!?%?$?!?%?%?$*?#?!?$?$*?%?*%?$?%?$?%?*%?$?%?*?%?%?$?+?%?$?(?)?%?*%?$?$*?%?$? ? !?%?$?&?&?&?%*? ? !?&?)?#?!?&?%?!?&?$? ?%? ?$?&?)? ?%? ?$?&?&? ?%? ?(?$?#?!? ?%? ?(?$? ?%? ?(?$? ?%?# $?(?(?#?!?(?#?!?(?#?!?(?#?!?(?(?(?(?#?!?#?!?!?&?!?!?&?!?#?!? ? ?!?#?!? ? ?!? ? ?!?#?!?$?#?(? ? ?!?(? ? ?!?#?!?(? ? ? !? ? !?(?(?(?(?$?(? ? !?$?(? ? !?(?(?(? ?!?!?$? ? !?$?#?!?(? ? !?(?*?(?*?#?#?(?(?(?(?*?*?*?*?#?#?$?(?%*?$?(?%*?(?(?(? ? !?(?(? ?(?#?(?!RadioFans.CN 收音机爱 好者资料库KANRINO.REF. NO.DESCRIPTIONPART NO.KANRINO.REF. NO.DESCRIPTIONPART NO. 7 ?(?#? ? !?$? ? !?(?$?$?*?(?*?(?*?(?(?(?(?&%?#?#?$?(?%*?$?(?%*?$?(?*?(?&?*?&?&?&? ?&?$+?&?$+?%?(?*?(?*?$?,$?*?,%?!?*?$?!?&?#?*?$)?&?#?*?$)?&?&$?*?$?&?&$?*?$? ?&? ? !?#?#!?!?#?$?%?!?$?)? ? !?$?#?)?#!?$?)?!?%+?%?+?#!?%+?%?+?#%?#?$?&?!?%+?%?+? ? !?$?$?$?$?$?#!?%?$?%?$?%?$?$?)?%&?(?(?(?#?#?#?(?$?(?$?(?$?(?#?(?(?$?(?$?(?&%?#?#?$?(?(?(?#?(?(?$?(? ?(?$?(?$?$?(?(?&?&?(?(?#?$?&?*?(?# ?&*&)?*+?$%?%?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)? !?$?$?$*-?)? !?$?$?$*-?)? !?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?$*-?)?$?$?%?%+?%?(?(?$?(? ? !?$?(? ? !?(?*?(?*?(?*?(?*?(?*?!RadioFans.CN 收音机爱 好者资料库KANRINO.REF. NO.DESCRIPTIONPART NO.KANRINO.REF. NO.DESCRIPTIONPART NO.?#?$?(?#?!?(? ? !?$?(?#?!?(? ? !?(?(?*?(?(?*?(?*?(?*?$?(?(?$?(?(?(?(?(?(?(?#?$?*? ? !?$?#? ? !?#?!?(?(? ? !?(?*?(?*?(?*?(?*?(?*?(? ?(? ? ? !?(?*? ? !?(? !?#? !? !? !?#? !? !?(? !? !?(? !?#? !?#? !?(?#?!?(?#?!?(?#?!?(?#?!?#?!?(?#?!?%?$?#?!?#?#?!?#?#?!?(?#?!?#?#?!?%?$?#?!?#?#?!?#?#?!?#?!?#?#?!?%?$?#?!?(? ? !? ? !?(? ? !?#? ? !?(? ? !?%?$?#? ? !?(?*? ? !?(? ?#?!?(? ?#?#?!? ? !?(? ?(?(?*?(?*?#?(?(?*?(?*?#? ? !?(?*?(?*? ? !?#?#?(?(?*?%?%?$?(? !?%?$?(? !?$?#+?%? ? !?%?$?(? !?%?#? !?%?#? !? ? ? ? !?%?$? !?%?#$? !?&?&*)?%? #?&*)?&?(?#?$)?&?(?#?$)?&?(?#?$)? !? ?&?%?#?!? ?&?%?#?!?&?(?#?$)?#?!? ?&?(?&?$)? !? ?&?&$?#?!?&?&?)? ? !?&?&$?&?)? ? !?&?*?&*)? ? !?&?*?&*)?#?!?%?(?*?%?#?%?#?%?#?%?%?+?(?(?+? !?(?# ?$?$? !?(?# ?$?$?(?(?!?#?!? ? ?!?#?!? ? ?!?#?! 8 RadioFans.CN 收音机爱 好者资料库KANRINO.REF. NO.DESCRIPTIONPART NO.KANRINO.REF. NO.DESCRIPTIONPART NO.? ? ?!?(?(? ? ?!?#?#?!? ? ?!?#?#?!?(?(? ? ?!?$?#?!? ? ?!?$?#?!?$?#? !? ? !?$?#?!? ? !?(?(?(? ?(? ?*?(?#?!?#?!?#?!?&?#?*?%?%?$?,?(?#?!?%?%?$?,?(?#?!?%?%?$?,?(?#?!?%?%?$?,?(?!?%?%?$?,?(?#?!?%?%?$?,?(?!?#?#?$?*?#?!?#?#?$?*?#?!?*?(?&?#?$?%?$?%?(?*?*?$&? ?$&?$+?$&? ?$&?$+?$?$?%&?$?$#?$?$?%&?$?$?%&?$?$?%&?$?$?%&?$?$#? ?%?&%?8 8AResistor CodeChip Resistor Part CodingFigureValue of resistorChip resistorWattageTypeTolerance1/16W1/10W1/8W1608212532165%5%5%CJCJCJFormLWt1.60.80.4521.250.453.21.6108118128 : A : ACHIP RESISTOR PART CODE0.55Resistor CodeDimensions (mm)Symbol1/16W10055%CJ1.00.50.35104LtW 9 RadioFans.CN 收音机爱 好者资料库TRANSISTOR ILLUSTRATION 10 2SA1235F2SC2714O2SC3052FCMBT5551CMBT5401CSD1306EKRA102SKRA107SKRC102S-RTKKRC104SEBC2SA1980GCDA1585BCCSC4115BCKTC3198GRE C B2SB13422SB13702SB16772SB1686B C E2SK360EDSGE C BCC55512SJ4602SK2541E C BG D S2SK2937B C E2SA1981Y2SC5343G2SD19332SD26192SD2642RadioFans.CN 收音机爱 好者资料库?RadioFans.CN 收音机爱 好者资料库 12 SCHEMATIC DIAGRAM 1 (MAIN 1/2)RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM 2 (FRONT / DECK) 13 RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM 3 (TUNER) 14 RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM 4 (MAIN 2/2: PT SECTION) 15 RadioFans.CN 收音机爱 好者资料库?RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM 5 (MAIN 1/2) 17 RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM 6 (FRONT / DECK) 18 RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM 7 (TUNER) 19 RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM 8 (MAIN 2/2: PT SECTION) 20 RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM 9 (MAIN 2/2: PT SECTION) 21 RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM - 10 (MAIN 2/2: PT SECTION) 22 RadioFans.CN 收音机爱 好者资料库?RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM 11 (AMP) 24 RadioFans.CN 收音机爱 好者资料库?RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM 12 (AMP) 26 RadioFans.CN 收音机爱 好者资料库?RadioFans.CN 收音机爱 好者资料库SCHEMATIC DIAGRAM 13 (AMP) 28 RadioFans.CN 收音机爱 好者资料库?SW5(CAM2)SW1(CAM1)SOL1SOL2SW2(CST1)SW3(REA)SW4(CST2)IC213IC113L H+R1SFR1TO FRONT C.B CN504(FFC504)CN11 3 5 7 9 112 4 6 8 10W1M1TAPEMOTORL H+E DECK C.BRadioFans.CN 收音机爱 好者资料库IC BLOCK DIAGRAM 30 RadioFans.CN 收音机爱 好者资料库FL (HNA-10SS19T) GRID ASSIGNMENT AND ANODE CONNECTION 31 GRID ASSIGNMENTRadioFans.CN 收音机爱 好者资料库 32 ANODE CONNECTION / PIN CONNECTONRadioFans.CN 收音机爱 好者资料库IC DESCRIPTIONIC, UPD780226GF-022-3BA / UPD780228GF-079-3BAPin No. Pin NameI/ODescription1SOL1ODECK1 solenoid output.2SOL2ODECK2 solenoid output.3O-MOTORODECK MOTOR ON/OFF output.4O-PB2ODECK2/DECK1 play output.5O-BIASOBIAS ON output.6O-RMTOREC mute output.7O-CD. ONOCD ON output.8O-TU. ONOTUNER ON output.9NC-Not c

    注意事项

    本文(Aiwa-NSXSZ200-cs-sm维修电路原理图.pdf)为本站会员(cc518)主动上传,收音机爱好者资料库仅提供信息存储空间,仅对用户上传内容的表现方式做保护处理,对上载内容本身不做任何修改或编辑。 若此文所含内容侵犯了您的版权或隐私,请立即通知收音机爱好者资料库(点击联系客服),我们立即给予删除!

    温馨提示:如果因为网速或其他原因下载失败请重新下载,重复下载不扣分。




    ADZZ
    关于我们 - 网站声明 - 网站地图 - 资源地图 - 友情链接 - 网站客服 - 联系我们

    copyright@ 2008-2025 收音机爱好者资料库 版权所有
    备案编号:鄂ICP备16009402-5号

    收起
    展开