Tektronix 494AP service manual O a O o O o o o, Sel, Value

GenerafInfornation - 4g4[l4g4Ap Service,Vol. 1

throughoutthe UnitedStatEsand in countrieswherEour products are sold. Several types of maintenanceor repairagreementsareavailable.

For example,for a fixed fee, a maintenanceagree- ment programprovidesmaintenanceand recalibration on a regularbasis. Tektronixwill remindyou when a productis due for r€calibrationand performthe service withina specifi€dtime.

. Tektronix emergency repair service provides immediate service when the instrument is urgently needed.

Contact your local Tektronix SeMce Center, representativeror sales engineerfor detailsregarding productservice.

Instrument Construction

Modularconstructionprovidesreadyaccessto the major circuits. Circuit boards containingsensitivecir_ cuits are either mountedon metal castings,each of which providesshieldingbetweenadjacentmodules,or they ars mountedwithin honeycomb-likecastings,withfeedthroughconnectorsthroughthe compartmentwall. All boards and assembliesplug onto a commoninter- connect board. Most adjustm€nlsand test pointsare aecessiblewhile the anstrumentis operationaland with the modulesor assembliessecuredin theirnormalposi_ tion.

Extendersare availablein an optionalServiceKit (see Maintenancesection under ServiceFixturesand Tools for Maintenance).Any moduleor board can be removedwithoutdisturbingthe structuralor functional integrity of the other modules. The extendersallow most circuit board assemblies to function in an extendedpositionfor serviceor adjustment. The circuit boards mountedon the metal castingcan be removed by removing the securing screws. All other circuit boards (which should require minimal service) are accessibleby removinga cover plateoverthe assembly or module.

Disassemblyof some modulesmay require specialtools and procedures. These pro_ cedur€s are located in the Maintenance section.

Circuits are isolated in shieldedcompartmentsto obtain and maintainth€ frequencystability,sensitivity, and EMI characteristics.While shieldinghetpsensuie spurious-freeresponse,the closenessof the circuits minimizeslossesand interactionswith otherfunctions.

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Compartmentsare enclosed on both sides by metal plat€s and interconn€ctionsbetweencompartmentsare made by feedthroughterminalsrather than cables. lf the compartmentsare opened,be sure that the shields andcoversare properlyreinstalledbeforeoperating.

Installation and Preparation for Use

The Installationsection of the manual provides unpacking information and the proceduresto prepare the instrum€ntfor use. lt also includesrepackaging information.

Changing Power lnput Range

The procedurefor changingthe input voltage range is describedin the Installationsection. Detailson how to changethe linefuse are alsogiven.

The powercord that is suppliedwith the instrument and the instrumentpowervoltagerequirementsdepend on the availablepow€r source (see Specificationsec- tion). Powercord optionsare describedin the Options section.

Replacing Fuses

Referto the Installationsectionfor linefuse replace- ment and the Maintenancesection for replacingthe powersupplyfuses.

Selected Components

Some componentsare selected,matched,or pre- conditionedto meet Tektronix specifications.These componentsare shownin the partslist and maycarrya Tektronix Part Number under the Mfr. Part Number column.

Selectedvaluecomponentsare identifiedon the cir-
cuit diagramand in the parts list as a	'SEL"
	value. The

componentd€scription lists either the nominal value or

arange of values. Selectioncriteriais includedin the Maintenance section. Selection procedures are includedin the AdjustmentProcedureor Maintenance sectionsof the manualas needed.

Assembly and Circuit Numbering

Each assembly and subassemblyare assigned assembly numbers. Generally,each componentis assigneda circuit numberaccordingto its geographic locationwithinan assembly.The ReplaceableElectrical Parts list prefixes these circuit numbers with the correspondingassemblyand subassemblynumbers.

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