Tektronix 494AP service manual Optioninstruments Only, AdjustOption0Z VR BandLevetino

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07)Move p2035 back to pins 1 and 2, reptace P3057,and disconnectthe iest oscilloscopefrom the ErrorAmplifierboard.

(18)ReduceSPAN/DVto 200kHz and ensurethat phaselock occurs, by the absenceof error rnessage and a sweep. Replacethe coverson the assemdly and reinstallthe modulein the lnstrument.perform the phaselock noisecheckas describedin the per- formanceGhecksection.

h.Check Strobe Drlver - Excessivenoise on the display and intermittentlock are indicationsthat the strobe pulsefrom the Strobe Driveris noisy or tow in amplitude.This can be causedby a mismaichin input g o$qut impedanceto th€ band-passfitter FL20Li4. The folfowing procedur€ is required if the filter or any componentthat affects the input or output impedanc6 matchis replaced.

(1) With the instrument in phase lock rnode (SPAN/DV200 kHz or tess),monitorTp1Og2with a test,oscilloscope.Note the amplitudeof the 5 MHz strobe signal. Amplitudeof the sinusodialstrobe signalis normaily5 V to 6 V peak-to_peak.

(2) lf the strobe signalamplitudeis low and noisy, changethe valueof selectcapacitorsC1016,C.t016; C1032 and C1034 to obtain the maximumstrobe pulseamplitudeat Tpl0g2. Thesecapacitorsrange from3.3 pF to 27 pF.

(3)lf the signatamplitudeis still tow,checkthe fre_ quencyat TP1012with a frequencycounter. Fre- quency must fie between 5.0067MHz and 5.0188MHz. The frequencyis a function of the ControlledOscillatorassembiyand counterU1OZ2.

OPTIONINSTRUMENTS

ONLY

17.AdjustOption0Z VR BandLevetino

(R3024on the VR Motherboard#2)

a. Setthe front-panelcontrolsas follows:

FREQUENCY .t00MHz

FREQSPAN/DV 200 kHz

REFLEVEL _20 dBm

MIN RF ATTEN OdB

AUTORESOLN on

TIME/DIVAUTO VERTCALDISPLAY 10 dB/Dtv

vtEW A/VEWB On

b.Placethe VR moduleon an extender,and con_ nect the cAL ouT signatto the 50o RF tNpUT via a 50O cable.

Adjustment Procedure- 4g4[l4g4fupServlceVol. 1

c.lt maybe necessaryto set th€ FREQUENCycon- trol to ke€p the 100MHzsignalat centerscreen.

d.RESETthE RESOLUTION BANDWIDTHtO 300 kHz,and the VERTTCALDtSpLAyto 2 dB/DtV.

e.Set the front-panelAMPL CAL for a 7-division excursionof the 100MHz signat.

f.Flemovethe 50O cable from the instrumentand reconnectthe cAL ouT signalto the 75o RF INpUTvia a 75O cabl€. Pushthe 75O RF tNpUTbutton.

g.Resetthe REFERENCELEVELto +20 dBmV

h.Adjust R3024on the VR Mother board #Z tor a 7-divisionexcursionof the 100MHz signal.

i.Disconnectthe 75O cable,disablethe 7SO input, and re-fnstallthe VR modulein the spectrum analyzer.

18.Adjust Option 42 Modute

(Cl016, Cl020 andCl024 in the Option42 Moctute)

This adjustmentn€ed only be done after the circuit boardin the modulehasbeenreplaced.

a.Connectthe test equipmentas shownin Figure

5-27.

b.Set the front-panelcontrolsof the test instrument as follows:

TR5O2
Output Level -dBm	25
Var dB	0

7L14

CenterFrequency 0110

FreqSpan/Oiv 2 MHz

Resolution 3 MHz

VerticalDisplay 2 dB

ReferenceLevel

DisplayAandB Off

DC503A

c h A

Term 50O

Slope + Atten

Coupl dc FreguencyA Autotrig

5-29

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