Cyrus CD T - PCB assemblies; Disc reading;decoder module and servo PCB

TECHNICALDESCRIPTION
©CyrusAudioLtdJun2014 6 CDtServiceManualIssue1
PCBassemblies
ThefollowingisabriefdescriptionoftheinternalPCBsfoundintheCDt.
TheservoPCBismounteddirectlyontotheCDmechanism,thisincludesthe CDloadermotor
andsleddrivers,theservodriverandCDdecoder.
Themain PCB is mounted in the baseofthechassisand containsthe powersupplies,optical
andcoaxialSPDIFoutputandtheuserinterfacemicrocontroller.
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Discreading/decodermoduleandservoPCB
The disc reading laser pickup is mounted in a motor driven slot loader, which receives its
operatingcommandsviatheservoPCB.

TheheartoftheservoPCBistheCDdecoderIntegratedCircuitIC401.Thisiscontrolledby
softwarerunningonthemainboardmicrocontrollerIC701viaanI
2
CBus.
Themicrocontrollersendshighlevelcommands(e.g.ReadTOC,Playtrack1)totheservoPCB
viaacommunicationbus.DiscloadingiscontrolledbythemicrocontrollerontheservoPCB.
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WhenadiscisinsertedintotheplayerthefirstthingthatneedstohappenisthattheTableof
Contents(TOC)ofthediscisread.Thisinformationcontainsthestartandendlocationofeach
trackonthediscfordiscnavigationpurposes.

InordertoreadtheTOCthelaserisswitchedonbythedecoderIC,andafocusrampis
initiated.Iffocusisfoundthenthediscmotorisswitchedonforashorttime,thenthePLLis
switchedonandthediscisacceleratedtofullspeed.Oncethespeedhadbeenachievedand
thePLLislockedontothedata,theradialloopisswitchedonandthesubcodewillberead
fromthediscandfedtothedecoder.

Thefocusandradialpositionsofthelaserspotarecontrolledbythedecoderbylookingatthe
diodesignalscomingfrom
theopticalpickup(OPU).TheseareD1,D2,D3andD4forfocus,R1
andR2forradial.TheerrorsignalfromthesediodesisusedtogenerateaPDMsignal.This
signalisthenfilteredwithalowpassfilterandamplifiedbythemotordriver(BA5984FP)to
movethe
actuators.

PowerforthelaserdiodeissupplieddirectlyfromthedecoderICwhichmonitorslaseroutput
andadjuststhepoweraccordingly.

Thereisasinglesystemclockontheservoboard,8.4672MHz.Thisisself‐generatedbythe
decoderIC.

Thereare2mainpowersuppliestotheservoboard,+5V_CDforthesignalprocessing
electronicsand+5V_MOTORtoIC402supplyingmotorandsledpower.The+5V_CDsupplyis
subregulatedto+3V3andsub‐sub‐regulatedto+1.8Von‐boardforthedecoderandother
electronics.
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