Tektronix 494AP service manual

Models: 494AP 494A

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V_COoutput apptiedto the ctock

...Ttg!g 'Theinput of

divide-by-scounterUaZZ.STROBE'er.raeLe fin"

frgm tlte Error Amplifierpermitsthe counterto operate when the line is low and is the means by wnich the microcomputercan turn the strobe pufsed on or off.

The .counter output couples throug'han- impedance matchingnetwork consistingof Ce0i0, f_iOar,C2Ogg, and C1032,to the inputof blndpass ntierfLzOO+.fne

matchingcircuitraisesthe tineimpedance

1Tp"g11g"^to about8200ohms.

Theory ol Opera{on - 4g4Al4S4ApServtce,Vol. 1

The output of the fitter drives another impedance matchingnetworkfor the gat€ inputof e2091. The out- put of Q2091drivestwo buffer amplifiersUt091A and U10918. Ul0918 drivesthe phase Gate circuitry.and Ul091A is reservedfor future applications.Capicitors Cl032 and C2105ar€ s_electedto providemaximumsig_ nal amplitudeat TP20BZ.

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Page 279
Image 279
Tektronix 494AP service manual