BBK MA-700s Service Manual

MA-700

Servicemanual

MA-700PrincipleandServicing

1.Unitcircuitprinciple

MA700isamiddle-levelactivespeaker,whichiscomposedofasubwooferspeaker,twofront
satellitespeakers,twosurroundspeakersandacentrespeakerandwithexcellentsoundeffect.Ithas
thefollowingfeatures:

2.1/5.1CHoutput;◆

◆◆Built-in5CHpoweramplifying,adaptabletoAC-3/DTSandstereomusicreplay;

With6CHvolumecontrolandseparatelevelcontrol,andwithtoneadjustmentfunction.

(1)PCBboardcompositionfigureoftheplayer

Theplayerincludesinputboard,outputboard,poweramplifierboardandcontrolpanel,inwhich,
inputboardandoutputboardarecomprisedofseveralterminals;themainpartispoweramplifierboard,
control,amplifyingpartoftheplayerandpowersupplyareallincludedonit.PCBboardcomposition
figureoftheplayerisshownasthefollowingfigure1.1.1:

CIRCUITCONNECTIONDIAGRAM

~14V

1.
0

2.

XS1

~14V

3.

POWERAMPLIFYINGBOARD

INPUTBOARD

XP2

SW

1. 1.
SR

2. 2.
SL

3.

C

4. 4.

R
L

GND

SW
SR
SL

3.

1.1.

2.2.

3.3.

C
R
L

GND

XS2

XS3

XP3

FRONTPANEL'SBOARD

SWSPEAKER

SW

XS4

GND

1. 1.
GND

2. 2.
C

3.

SR

4. 4.

L
R
SL

OUTPUTBOARD

GND
GND
C

3.
SR

XP4

L

1.1.
R

2.2.
SL

3.3.

Figure1.1.1PCBboardcompositionfigureoftheplayer

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(2)Principleblockdiagramoftheplayer

Theprincipleblockdiagramoftheplayerisshownasinthefollowingfigure1.2.1:signalsarriveat
electronicvolumeandtoneadjustmentcircuitthroughinputterminalfortoneandvolumeadjustment,
andthenaresenttopoweramplifyingcircuitforamplifyingoutput.Theinformationreceivingand
sendingofCPUcontroltheworkingstateoftheplayeranddrivedisplaycircuittodisplay.

Electronic

Signal
input

volume

&

tone

adjustment

Power
amplifying

Output

CPU

Receiving,displaypart

Figure1.2.1Principleblockdiagramoftheplayer

(3Signalblockdiagramoftheplayer）

Signalblockdiagramoftheplayerisshownasinthefollowingfigure1.3.1:

BLOCKDIAGRAM

MAINPOWERAMPLIFYINGBOARD

INPUTBOARD

LL
R
C
SW
SL
SR

5.1CH

INPUT

VOLUME
CONTROL

LL R SLSR

C

SW

L R

LPF

AMPLIFICATION

LRSLSR

POWER
AMPLIFICATION

C

POWER
AMPLIFICATION

SW

POWER
AMPLIFICATION

L

R

SL

SR

C

SW

OUTPUTBOARD

CPU

REMOTE
CONTROL
RECEPTION

FRONTPANEL'SCONTROLBOARD

Figure1.3.1Signalblockdiagramoftheplayer

LED

POWER
SUPPLY

DISPLAY

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(4)Powersupplycircuit

Becauseoftheoutputpoweramplifyingofsubwoofer,thisplayeradoptsroundtransformerto
supplypowertothemachine.Agroupof18Vvoltageisoutputtedfromtransformer,afterrectification
filtering,+22VvoltageisoutputtedtosupplypowerforpowerICTDA8947andICTDA9843.

Onepathoftheoutputted22Vvoltage,throughcurrentlimitingresistorR101,voltageregulating
diodeVD104andcapacitorC108,outputs+9VvoltagetosupplyforICTDA7448;theotherpath,
throughR100andvoltageregulatingdiodeVD105,outputs5VvoltagetosupplypowerforCPUand
controlpanel.

(5)Signalinputandvolume,toneadjustmentcircuit

This playerhas6-channelsignalinput;thesignalinputtedineachchannel,throughfiltering
capacitor,isdirectlysenttoICTDA7448forvolumeandtoneadjustment.Inaddition,onesignalis
pulledtoLandRmainchannelindividuallyandoverlappedtoSWinput,thus,whenthereisonlyL,R
channelinput,2.1outputeffectmayalsobeachieved.

ICTDA7448isaICwithseparate6-channelvolumeandtoneadjustmentfunction,anditsgainis
adjustableby095DB,whichisadaptabletohometheatreseriesproducts.Ithasstrongpointsoflarge
powersupplyrange,smallpowerconsumptionandwideapplicabletemperaturerangeandisagood
performanceIC.

(6)Amplifyingcircuit

SignaloutputsafteradjustmentofTDA7448,inwhichmainchannelsignalissenttoN101IC
TDA9843forpoweramplifying,butcentre/surroundsignalissenttoN106ICTDA8947foramplifying
afterfiltering;subwoofersignal,firstlythroughdipping(clippingcircuitiscomposedofdiodeVd110and
Vd113),thenthroughpre-processingandthenissenttoN102ICTDA9843.Thefunctionofdippingisto
preventtheloudspeakerfrombeingburntdownbecauseoftoolargepowerofsignalafterbeing
amplified.AmplifyingICissuppliedpowerbysinglepower,sotheamplifyingoutputtedsignaliswithDC
andfilteringisneededbeforeoutputtingtoloudspeaker.

ICTDA9843Jisadual-channelpoweramplifyingICwithstandbyandmutemode,withoutpower
on/offpercussionandwithfunctionsofshort-circuitandover-heatprotection,whichmaybeusedto
effectivelypreventICbeingdamagedinabnormalconditions.ThisICmayprovidemax20Wpower
outputforeachchannelincommonoutputmode.WhenBTLoutputisadopted,powermaybeupto40W,
inadditionthisICiswithpowerfulanti-ripplefunctionandpowerisverysmallinstandbystate.

ICTDA8947Jisa4-channelpoweramplifyingICanditsmainfeaturesaresimilartoICTDA9843J,
butthepowerthatcanoutputislarge,andsinglechannelmaybeupto25W.

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。

(7)Controlcircuit

CPUofthisplayeradoptsICAT89C2051tocontroltheworkingofthewholemachine.6CHvolume

adjustment,channelleveladjustment,mutecontrol,digitaldisplayandremotecontrolfunction
realizationareallcontrolledthroughCPU.ThisICisalowvoltageandhighperformanceIC,whichisa
singlechipwhichadoptsCMOStechniqueandflashwith2Kbyteandreadablestorage,ithas15I/O
portsand6interruptsources,andwithlowpowerconsumptionandstandbymode.

(8)Resetcircuit

ThisplayeradoptshighlevelresetandutilizesthefeaturethatvoltageofcapacitorC109cannot

jump.Atthemomentofpoweron,capacitorvoltagecannotjump,baseelectrodeoftriodeV100islow
level,triodeisnoton,and5Vvoltaheisaddedtopin1ofCPUthroughresistorR114.Forcapacitor
chargeandvoltageofanodeofcapacitorincreasesgradually,whenvoltageisuptoacertaindegree,
voltageregulatingdiodeisreverselyontomakebaseelectrodeoftriodehighlevel,triodeison,voltage
ofresetpinchangesintolowlevelandresetfinishes,shownasinthefigure1.8.1:

+5V

R103

18K

VD116

R102

22K

Figure1.8.1Resetcircuitdiagram

3.3V

C109

4.7u/50V

R114

4.7K

V100

9014

(9)Remotecontrolcircuit

Thestateofthisplayerisadjustedmainlybyremotecontrol.Signalreceivedthroughremotecontrol

issenttopin6ofCPU,throughCPUinternalprocessing,sendsoutcontrolsignaltoadjustthevolume
andtoneoftheplayerthroughpin8,9andcontrolspaneldisplaythroughP1porttomakeusersknow
whichstatethemachineisin.Inaddition,mainchannelandcentre/surroundmuteiscontrolledthrough
pin2,3ofCPU.

(10)Controlpanelcircuit

Controlpanelofthisplayeriscomposedbyaremotecontrolreceiverandadigitaltube.Thisplayer

isoperatedthroughremotecontrol,soremotecontrolreceiveristheuniquerouteforman-machine
conversation.Digitaltubedisplaystheoperationbeingperformedandstateoftheplayer.

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(11)Poweron/offmuteandmutecircuit

Poweron/offmute:shownasinthefigure1.11.1,atthemomentofpoweron,voltageoftwoendsof
capacitorC169cannotjump,solowleveliskeptnottochangetomaketriodeV106cutoffandV105on
tomakeMUTE1outputlowleveltopulldownLRMandSCMsignalleveltocausemute.Whencapacitor
ischargedtomakeVD1095.1VvoltageregulatingpipeandV1049014on,baseelectrodelevelofV105
ispulleddowntomaketriodeV105cutoff,MUTE1outputshighlevelandmutefinishes.Itisthesame
withthatwheninpoweroff.CapacitorC169dischargesquicklythroughdiodeVd112tomakeitspositive
voltagedecreasequicklytomaketriodeV106cutoff,V105on,MUTEoutputlowlevelandmuteis
opened.Thatnopercussionsoundappearswhenpoweronandoffisrealizedthroughthiscircuit.

C168

4.7u/50V

VD112 1N4148

100K

R107

R106

4.7K/0.25W
VD109

5.1V

C169

10u/25V

Figure1.11.1Poweron/offmutecircuitdiagram

R165

47K

R138

47K

+22V

9014C

V106

R167

10K

R140

270
V105
S8050

C172

4.7u/50V

Mutecircuit:themutefunctionofthisplayerisrealizedthroughthemutesignalsentoutbyCPU.
WhenpressingMUTEonremotecontroller,remotecontrolconnectstoCPUandsendouthighlevel
frompin2,3ofCPUtomakeV107,V108on,LRMsignalispulleddownto15Vfrom22V,

LRMsignalis
senttopinODEofTFA9843,muteofTFA9843opens.ForTDA8947modeselectionfunction,please
refertoICTDA9843materialsfordetails.

2.Troubleshooting

Electroniclineinsidethismachineissimplewithoutcomplicatedcontrol,detectcircuits,sosignal
injectionisadoptedforthismachine'sservicing,thatis,signalisaddedtosignalinputendandthen
followssignalflow.Ifsignalinterruptssuddenlyinacertainplace,andthetroubleliesinthisplace
basically.Therefore,forservicingofthismachine,doaccordingtothefollowingprocess:

(1)Checkwhetherpowersupplypartisnormal,thatis,checkwhetherpowersupplyof22V,9Vand
5Visnormal;

(2)Forabnormalities,suchasthereisnosound,inconditionsofnormalpower,youshouldcheck
whethermutelevelisnormal,thenconsiderwhetherotherelementsareabnormal;

(3)Formachinewithabnormaldisplay,firstlymakesurewhetherdigitaltubeisabnormal,then
checkwhetherCPUisabnormal.

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3.Troubleshootingprocess

(1)Troubleshootingprocessfor“Nooutput”isshownasinthefollowingfigure3.1.1:

Nooutput

Check

whetherpowersupply

isnormal

Y

Check

whethermuteisnormal

Y

ChangeN103

Figure3.1.1Troubleshootingflowchartfor“Nooutput”

N

Checkandrepairvoltagepart

N

Checkeachpolartubeof
mutecircuit

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