Cyrus 8 DAC - FAULT FINDING; Layout of the amplifier; Dismantling the amplifier; Initial precautions and first tests

FAULTFINDING
©CyrusAudioLtdJun2014 12 Cyrus6DAC,Cyrus8DACservicemanualIssue1
The amplifiers are complex, microcontrolled products using small‐scale SMD technology. Do
not attempt anyfault‐finding orrepairon oneofthese productsunlessyou are acompetent
audioengineerwiththecorrectSMDrepairtoolsandtrainedtofault‐findonthisequipment.
This fault‐finding guide is not exhaustive, but should help a competent engineer trace faults
within the amplifier. If you require more technical help than this guide, contact the Cyrus
ServiceDepartment.
CAUTION
The high‐efficiency heat‐transfer insulation pads fitted between the power amplifier output
transistors and the chassis of the amplifiers are designed to soften, melt and bond to the
transistorandheatsinkwhentheamplifierfirstheatsup. This istoenablethepadstofillany
pits in the surface of the heatsink and provide an excellent thermal bond between the
transistorandheatsink.ForthisreasonanypadmaterialmustALWAYSbecompletelyscraped
from the heatsink and the pads replaced if the seal is broken between the transistor and
heatsink,as they will notre‐bond.Conventionalpads
andgrease are much less efficient heat
conductorsandarenotanacceptablesubstituteforthecorrectpads. Useofalternativepads
will risk future  failure of the amplifier. Always obtain original pads from the Cyrus Service
Department.
Layoutoftheamplifier

The amplifier is constructed with the analogue pre‐amplifier, power amplifier and power
supplylayingon the main PCB fixed inthe base of the chassis, andasmallersubPCBlocated
overthisthatincludestheheadphoneamplifier,thepowersupplyforthedisplaybacklight,the
circuitry for the digital inputs and the D/A converter. The analogue audio output from the
digital audiosection of the sub PCBconnects to thepreamplifier onthe mainPCB through a
cable.
ThecircuitrythatcontrolstheamplifierislocatedonthefrontpanelPCBwiththeLCDdisplay.
Dismantlingtheamplifier

Basic tests, alignment and fuse replacement are possible without removing the sub PCB. All
alignmenttestpointsonthemainPCBandtherightchanneladjustmentpresetsareaccessible
aroundtheborderofthesubPCB.Theleftchanneladjustmentpresetscanbereachedthrough
anaccessholeinthesubPCB.
Foraccesstotestorrepairthepreamplifieror poweramplifierstages,thesubPCBmustfirst
beremoved.WiththesubPCBremoved,theamplifier  willcontinuetofunctionasnormalfor
testandrepair,butwithoutthedisplaybacklightordigitalinputs.
The sub PCB cannot simply
 be unplugged from its main PCB connector without damage. To
removethesubPCBleavingthemainPCBinthechassis,removethescrewssecuringtherear
paneltothesubPCB and the two along thetopedgefixingittothechassis.Removethenut
securingtheheadphonesocket(special toolrequired).Oncethescrewsareremoved,therear
panelcanbetiltedbackslightlytoallowclearancetoremovethesubPCBfromitsconnector.
CAUTION:Whenre‐fitting thesub‐PCB,takeparticularcaretoensurethattheconnector pins
arecorrectlyaligned.Misalignmentofthepinswillcauseconsiderabledamagetothesub‐PCB.
Initialprecautionsandfirsttests

Before connecting power to an amplifier that is suspected to be faulty, ensure that
loudspeakersandloadsaredisconnectedfromthespeakersocketstoavoiddamagingthem.