Tektronix 494AP service manual O o o o O a o o o, A a o A o O o o, LNorE-l

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AdJustmentProcedure- 4g4[l4g4Ap Service Vot. 1

Flgure5'15.Adiu3tmontson the rear of tre VariabreResorudonmodure.

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(3) Connectthe output of the VariableResolution moduleto the input.of lhe Log Amplifierassembly by connectinga cable from J6g2 on the Variable ResolutionModule to J621 on th€ Log & Video

-S-t+;.

Amplifierassembly{seeFiguresS-10and

(a)Applythe CAL OUT signatto th€ RF tNpUT,and set the SpectrumAnalyzercontrolsas follows:

FREQUENCY100MHz

FREOSPAN/DVS0kHz

RESOLUTTONBANDWTDTH10kHz

REFLEVEL-20dBm

MtNRF ATTEN0 ctB

VERTICALDTSPLAY 2 dBl}tv

b. Resetthe REF LEVELfor a sevendivisionexcur_ sion Tune the display to center screenand activate

SAVEA.

- c. Change the RESOLUTTONBANDWIDTHto 3 MHz and FREQ SPAN/DVto 1 MHz. Reset REF LEVELto bringthe signalamplitudeto aboutthe same levelas th€ 10kHz response.

-d. Adjustthe four tuningscrews(capacitors)on the 110MHz Bandpass Fitter (FL361foi tire best 3 MHz fi-lter response (3 MHz bandwidth *600 kHz, 6 dB

.

down) that is centered about the 10 kHz reference. Referto Figure5-16.

e.Change the RESOLUTTONBANDWIDTHro 1 MHz and FREQ SPAN/DVto 500kHz. Reset REF LEVELto bringthe signalamplitudeto aboutthe same

levelas th€ 10 kHz response.

f. AdjustC1034,C1044,and C1046,and R1027on the VR 2nd FilterSelectboard(Figure5,15)for the best 1 MHz filter response(1 MHz bandwidth,3 dB down. that is centeredabout the 10 kHz reference).Referto Figure5-16.

g. Change the RESOLUTTONBANDWTDTHro 100kHz andreset REFLEVELto bringthe signatampti- tudeto aboutthe samelevelas the l0 kHz response.

h. AdjustC5055,C5048,and C3041on the VR 2nd Filter Selectboard (Figure5-17)for the best .lOO

kHz filter response(100kHz bandwidth,3 dB down, that is centeredaboutthe 10 kHz reference).Refer to Figure 5-16.

i. RESETth€ RESOLUTIONBANDWIDTHtO 1OKHZ, deactivateand reactivateSAVE A to re-establishthe 10 kHzreference.n ',-' -5 -

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J. Adlust 10 Hz BandpassFllter

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All adjustablecapacitorson the Bandpass Fifterboard in the 10 Hzfi00 Hz Bandpass Filterassemblyshouldbe set to midrangeif the filter is badly misadjusted.This minim-

izesthe numberof times interactingadjust- rnents must be repeated to eliminate interaction.

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