Tektronix 494AP service manual O o o, Freospan/Dv Max

Malntenance- 4g4A/4g4ApServlceVol.i

1st ConverterBias

This procedurepresetsflatnessfor Band4, Band5, and Bands '1,

2, and 3,: then adjusts the Start (OHzi

Responseamplitudeandoverallflatness.

These adjustmentsshould only be performed after replacem€ntof the Dual Diode Assem'blyin the First Converter. Test equipmentneeded to adjust the 1st Converterare listedin Table6-9.

a.Removethe lst Converterassemblyfrom the SpeetrumAnalyzer.Connectthe assemblyt6 the Spec- trum Analyzeras shownin FigureG26.

b.MonitorTp1011on the lst LO Driverboardwith a_voltmeter(meter ground at crt shield). See Figure 6_ 27 tor thelocationof Tpl011.

c.Setthe SpectrumAnalyzercontrolsas follows:

TIME/DtVAUTO REFERENCELEVEL -30dBM FREQUENCYRANGE 5.4-18 GHz(Band4)

FREOSPAN/DV MAX

VIEWA andVIEWB ofi

MINRF ATTEN 0 d B

PEAK/AVERAGE FullyGlockwise

d.Preset Bias 2 R1022 (Figure 6-271tor a meter readingof -0.25V.

e.Change the FREQUENCYRANGEto Band s (15-21 GHz.)

f.Preset Blas 3 R1026(Figure6_27)for a meter readingof -0.25V.

g.Resetthe SpectrumAnalyzercontrolsas follows:

FREQUENCY2MHz FREOUENCYRANGE 0-1.9 GHz(Bandt)

FREOSPAN/DV 200 kHz

VIEWA andMEWB On WIDEVIDEOFILTEH on

Calibratethe power meter before making measurements.

h.Connect a 50O cable from the output of the SG503to the PowerMeter(Sensor.)

6-44

i.Set the SG503output frequencyat 2 MHz, and outputlevelat 0 dBm as indicatedon the power Meter.

j.Disconnectth€ 50O cablefrom the power Meter and connect the cable to the SpectrumAnalyzerRF INPUTthroughthe 10dB and gdB attenuators.The CENTERmay haveto be resetto bring the 2 MHz sig- nalto centerscreen.

kActivate SAVEA to save the bandwidth of the 2 MHz for reference.

l.MonitorTP1011on the lst LO Driverboardwith the voltmeter.

m.Preset R1013 on the 1st LO DrivErboard for

-1.0 V at TP1011.

n.Reset FREQUENCYto 0 (0.00MHz)to bringthe 0 Hz spurto centerscreen.

DO NOT ALLOW THE VOLTAGE AT TPlOll TO EXCEED+0.1V WHILE THE FOLLOWINGADJUSTMENTSARE BEING MADE.

o.Adjustthe tuningscrewon the 1st Mixer assem- bfy and R1013,R1022,and Rl026 on the 1st LO Driver board to match the response of the 0 Hz spur to the bandwidthof the 2 MHz reterence(SAVEA disptay).

Auxiliary Synthesizer VCO Adjustment

a.Monitor TP1066 on the Auxitiary Synthesizer boardwith a voltmeter.

b.DisconnectP261, P1039,and p1060 from the AuxiliarySynthesizermodule.

c.Disable frequency corrections by pressing <Blue-SHIFT>10 dB/DlV.

d.Enable the Auxiliary Synthesizerby pressing <Blue-SHIFT> pulse STRETCHERand selectingmenu item #4.

e.Adjust Cl070 on the AuxiliarySynthesizerboard for +5 V at TPl066.

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