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829 MHz Converler Maintenance

Some circuit boards in this assembly contain critical-lengthprintedelements. Whendamaged,these elementsare usuallynot repairable;therefore,the cir_ cuit board must be replaced. even itroujfr repfacement

bgards .are precalibrated and ,"p"i, be accom_

plish.ed.byreplacingthe board,we "-"n recommendsending

the instrumentor assemblyto your Tekironix

-Service

Centerfor repairandcalibrition.

The 829MHz band-passfilter in the lF section,and the 7'l9MHz LO in the -Lo section,requireadjustment only if the board has been damaged'J,

ponents (transistoror varactor) hive ""tiu" "o*- been reptaced.

The following describes prepaiation foi service and replacementprocedures.The first two steps describe how to gain accessto eitherthe LO or the lF section; the.remainingst€ps describeadjustmentprocedurefor eachsection.

1. To gain access to the LO section:

a. Switch POWERofi; use a 5/64 Ailen wrenchto loosenand removethe coverscrews.

b. Removethe cover.

c. Referto step 3 (withinthis procedure)for adjust- ment procedure.

2. To gain access to the lF section

a. Switch POWERoff; use a 5/16 inch wrenchto disconnectand remove all coaxial connectorsto the 829 MHz converter.

b. Removethe six mountingscrews,unplugthe input power connector P4OSO,ihen remove the g2g MHz converterassembly.

c. Turnthe assemblyover and removethe coverfor the lF section.

d. To troubteshootor calibratethe circuits,set the assemblyat a locationso the input power plug p4050 can be reconnectedto the Mother boarO. Be sure to observeplugorientation(pin1 to pin 1).

e. Referto step 4 (withinthis procedure)for adjust- mentprocedure.

3.719 MHz Osciilator Range Adjustment

a. Adjustmentrequires the foilowing test equip- ment:

^frequencycounter with a frequency range to 1 GHz (ninedigit readout),sensitivityof 20 mV rms for prescaledinput or 15 mVrms tor a direct input (suchas TEKTRONIXDc 510 counterwitha Dp 501 pres.calee;a digital voltmeter with a g.5 digit readout(suchas TEKTRONIXDM 502A);test teads

Maintenance- 4g4N494ApServtceVol. 1

for th€ DVM,a 50O coaxialcabtewith bnc connec_ tors ffektronix part number 012-04g2_00)and a sma male-to-bncf_emaleadapter Cfektronix part number015-1018-O0).

b. The 2nd LO range is 714.5 MHz to 223.5MHz (withthe coveroff). 71g MHz is the optimumcenterfre_ guen!{. . Frequencyof the osciltatoris controlledby the TuneVoltsfrom the 25 MHz phaseLockcircuitltoiateO at TPl011)whichvariesfrom+5 V (lowend)to +11.gV (high end) with +6.75 V to +2.5 V as the timits for op€rationat 719MHz.set the digitalvoltmeterto meas_ ure 12V thenconnectatbetweenTplolt (Figure6-12)andground.

c.Disconnectthe 100MHz referencefrom the grd Converterby unpluggingp235 (Figure6-12). The oscit_ lator shouldgo to its upperlimit and the voltmeterindi- cateabout11.9V.

Figure6-12. 829MHzLOtestpointsandconnectors.

d.Connectthe 75 MHz-1 000MHz inputof the fre- quencycounterthrougha 50O coaxialcableto the front panel2ndLO OUTPUTconnector.

e.Minoradjustmentsto the oscillatorfrequencyare made by shorteningthe U-shapedtransmissionline stub, off the main line. Graduation marks (see Figure6-12)along the side of the stub providea guide to calculatefrequencycorrection. Each minor mark from the end or cut across the stub, representsan approximatechangeot 2 MHz.

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