Tektronix 494AP service manual O o O o o o

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Product:see llstdate:2-22-88Chg.Ref:M6391r

Replacethedescriptionfor the DeftectionAmptifiers(Diagram27) withthetottowing.

DEFLECTIONAMPLIFER(Diagram278)

Referloiheblockdiagramadjacenlto Diagram27aswellastheschematicdiagramThe.DeflectionAmplifier receivesverlicalsignalinlormationtromtheverticalsectionoflheDigitalStorageoftheVideoProcessoi,and horizonlalorsweepboardThe.ReadouldataforthedisplaycomestromtheCR1ReadoutcircuitsThe.output of the DeflectionAmplifierdrivesthe crt dellectionplates.The amplitierscontainlhe switchingcircuits necessarylo performtheselectionfunctionsandtheyalsocontaintheamplifierstagesneededtoproductthe defleclionplatedrivesignals.

HorizontalSection

SignallinesHORIZONTALSIGNAL(fromlhedigitatstoragecircuitsthroughedgeconnectorpin49)and Sweep(fromtheSweepcircuitthroughedgeconnectorpin51)areapptiedto switChU7O55AU705s,.under conlroloftheSTORAGEOFFsignal(fromthedigitalstoragecircuitsthroughedgeconnectorpin7),setects eithertheHORIZONTALSGNALorSWEEPinputThe. SWEEPsignatissetectedwhentheSTORAGEOFF lineis pulledlow.ResistivedividerR7065and R7070reducethe selectedsignaltrom1V/divto o.Sv/div. U7073bufferstheselectedsignalThe.sefectedsignalgoesouttotheHORTZOuT rear-panetconneclorvia pin1 and2 on P6100,P6090andpin48oftheedgeconnectorU7073.apptiesthesignatto switchU70558. TheHORIZR/OOFFsignal,tromtheCrtReadoulselectsbetweenthesetwosignati.WhenR/Oisfloating or pulledhigh,theswitchtransmilsthesignallrombufferU7073to lheshaperWhen.thetineispuledtow, it selectsthe HORIZONTALR/Osignat.

U7055appliesthe signalto a shapernetworklo compensatelor non-linearityin the crt deflection characteristicsThis.networkconsislsof resistorsR5059,R5058,R50S7,R4061,iaosg, andR5062,plus diodesCR4052,CR4051,CR4958,andCR4056The.HORIZONTALPOStTtONvottage,fromthefrontpanel viaedgeconneclorpin 47,throughresistorR5056,is appliedto theshapercircuitso tneshapeconection lactorrelateslo thecrtdeflection.

TheshapedsignalisthenappliedlhroughpreamplifierU2055tothedeftectionamplitiercircuitsHORTZ.gain adjuslmentR1055,calibrateslhe amountof gaincompensationrequiredforproperdeflectionsensitiviiy.

The horizontaldetlectionamplilierconsistsof two circuitssimilarto eachother,one for eachhorizontal deflectionplate.Onecircuitis an invertingamplitier,the otheroperatesin-phaseInputs.to U2030of the invertingsidearethroughtheparaltelcombinationol resistorsR1039andR1038andcapacitorC1040The. seriesconneclionof resistorR1038and variablecapacitorCl040 provideshigh-frequencyresponse compensatio- capacitor c2047controtshigh{requencyfeedback.

fnpullo lhe non-invertingsideof theamplifieristhroughresistorR1025to u2030.R1o?'zandR2020setthe dc levelfor thefeed-backloopto the plusinputsideof the amplifierVariable.capacitorC1030provides adjustmentto sel lransientgain.Highfrequencyfeedbackis controlledby capaciiorC20tO.Gainol each amplifiersectionisapproximately20.(Horizontaldellectionsensilivityoflhecrtisapproximately21.3v/divper side.)

SignalswithlowrateofchangedrivetheoulputFETtransistorsthroughR3038,astherateol riseincreases, the dropacrossR3040increasesand whenit reaches0.6V,either03047 or e3046 biasedon. These transislorsprovidehighcurrentdrivefortheoutputlransislorsWhen.thesignalrateol changeislow,04030 drivesthecrtdefleclionplatesandQ4040providesbiascurrenlfortheamplitier,Astherateorriseincreases, 949?1couplesthesignaltothegateof 04040.04040providestheposilivedrivetothedeflectionptate,and 04030providesthenegativedrive.Eachoutputtransislorcanprovidea200Vexcursioninapproximately1ps.

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