Tektronix 494AP service manual

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5.Openthe diodepackage. Usea pairof tweezers to grasp th€ diodeassemblyby its side,and placeit on a static-freesurface.Grasp t-hesideof the'"rr"rOty with^thefingers. Avoid coniact with the diodes. Insert the 8-32 screw.

6, Orientthe diode assemblyso the threecontact tips are arignedwith their respictive contactsin the mixer; then, using the index fingersof both handsso equal pressureis applieO,presJ the subassembtyinto place.

7, Insert the four mountingscrews, then replace and tighten the three coaxial ionnectois to g in-lbs. Remountthe lst Conv€rterassemblyOy instattingitre two mountingscrewsthat hold ttre aisembtyto th; RF deck.

-. .8. The Spectrum Analyzer may not meet the flatnessspecificationafter the DuatCIodeassemblyis replaced. Refer to MATNTENANCEADJUSTMENTSin this_seetionfor a procedurefor adjustingconverterbias and flatness.

Replacing the Crt

1.Removethe snap_inprinted bezel and crt tight

filter.

. 2: Use an g/64 inch AllEn wrenchto removethe four bezelscrews,unplugand removethe innerbezel.

3.Unsolderthe ground wire from the front panel casting and unplugthe crt cables at their respective ?oarg_connections(High Voltage module, Deflection Amplifierboard,andZ-AxisUoarO;.

4.Slidethe crt, with its shletd,out throughthe front

panel.

5.Removethe crt shieldas follows:

a.Remove the tube base cap and unplug the socket.

b.Removethe two side screwsthat holdth€ upper shieldin place,thenremovethe shield.

c.Loosenthe screwsthat clampthe plasticbracket aroundthe crt, then removethe bracket.

. 6. Jnstallthe plastic bracket so the back on the ctamp is 5.07inchesfrom the back of the cn socket guide.

- 7. ReplacEthe crt shield plus the socketand base shieldby reversingthe removalprocedure.Thefinished crt ^assemblylength. with cap installed,must equal 11.05inches.lf it is longer,the assemblymayshortcir_ cuit the DeflectionAmplifier circuit boird when it is installed.

. 8.. Place_the spectrumanalyzeron its rear panel then loosenthe four crt blue ptasticmountingblockson the front castingso they can be readilypositionedwhen the crt is installed.

Maintenance- 4g4Ll4g4ApService Vol. 1

9. lnstallthe crt with shield assemblythroughthe front panel;seatthe wedgeson the siOeof the crt, into the blueplasticrnountingblocks.

10. Positionthe cast bezel and implosionshieldin placeto €nsurethat there is clearancebetweenthe crt face and the bezel, fl'hebezel must bottom on the frontcasting.)

It.is very importantthat the four mounting blocks are loose enough so the bezel retainingscrews can be tightenedwithout the bezeltouchingthe crt face. lf not the crt or the bezelmay crack whenthe screws aretightened.

11.Removethe bezel and tightenthe mounting blockscrewsevenlyin a cross pattemto approximatel!

8in-lbs.Make sure the crt stays centereOin tf,e Utui plasticmountingblocksas the screwsare tightened.

12.Replacethe bezeland implosionshield,recon- nect cablesto their respectiveboard connectors,and resolderthe groundleadto its terminal.

13.Replacecrt lightfilterand snap-inprintedbezel.

Repairing the Crt Trace Rotation Coil

The tracerotationcoil is part of the crt assembly.tf the coil is damagedbeyondrepair,the crt with the coil mustbe replaced.

'finish"

.lf the (red)lead is broken,removethe tape and unwindone or two tums so it can be resplicedand solder€dto the leadwire. Rewindand retape.

.lf the "start"(black)lead is brokenand the lead is too shortto re-splice,atempt to fish out the brokenend so one or two turns can be unwound,re-spliceand solderto the lead;thenrewindand retape.

Front Panel Assembly Removat

It is not necessaryto removethe front panelassem- bly to replace any of the push buttons. (Refer to ReplacingFront Panel pushbuttons,that follows this procedure.)The crt is removed with the front-panel assembly,

1.Set the instrumentuprighton its rear panel,then unscrewand removethg mountingnuts and washers for the RF INPUT,EXT MIXER,lst Lo oUTPUT.and 2nd LO OUTPUTconnectors.

2.Removethe two screwsthat holdthe front panel to the RF deck(centerand left side).

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