Tektronix 494AP service manual O o o, Maintenance- 4g4Al4g4ApServlce Vot

Maintenance- 4g4Al4g4ApServlce Vot. 1

PREVENTIVEMAINTENANCE

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Preventivemaintenanceconsists of cleaning,visual inspection,performancecheck, and if neededa recali- bration. The preventivemaintenanceschedule that is establishedfor the instrumentshould be basedon the environmentin which the instrumentis operatedand the amount of use. Under av€rage conditions (laboratory situation)a preventivemaintenancecheck should be performedevery 1000hoursof instrumentoperation.

Elapsed Time Meter

A5000 hour elapsed time indicator, graduated in 500 hourincrementsis. installedon thEZ-AxislRFInter- face circuit board. This provides a convenientway to check operating time. The meter on new instruments may indicate from 200 to 300 hours elapsed time becausemost instrumentsgo through a factory burn-in tim€ to improvereliabitity.This is simitarto usingaged componentsto improvereliabilityand operatingstabil- ity.

Cleaning

Cleanthe instrumentoften enoughto preventdust or dirt from accumulatingin or on it. Accumulationof dirt and greaseacts as a thermalinsulatingblanketand preventsefficientheatdissipation.lt also provideshigh resistanceelectricalleakaggpaths betweenconductors or componentsin a humidenvironment.

Exterlor. Clean the dust from the outside of the Instrumentby wipingor brushingthe surfacewith a soft cloth or smallbrush. The brushwill removedust from around the front-panelselector buttons. Hardeneddirt may be rernovedwith a cloth dampenedin water that contains a mild d€tergent. Abrasive cleaners should not be used.

Interlon Clean the interior by looseningaccumu- lated dust with a clry soft brush, then remove the looseneddirt with low pressureair to blow the dust cl€ar. (High velocity air can damage som€ com- ponents.) Hardeneddirt or grease may be removed with a cottontipped applicatordampenedwith a solu- tion of milddetergentin wat€r. Do not leavedetergent on critical memory components. Abrasive cleaners should not b€ used. lf the circuit board assemblies needcleaning,removethe circuit board by referringto the instructionsunder CorrectiveMaintenancEin this section.

After cleaning,allow the interior to thoroughlydry beforeapplyingpow€rto the instrument.

Do not allow water to get inside any enclosedassemblyor compon€ntssuchas thE hybrid assemblies, RF Attenuator assembly,pot€ntiometers,etc. Instructions for removingtheseassembliesare provided in the CorrectiveMaintenancepart of this section. Do not cleanany plasticmaterials with organiccleaningsolventssuchas ben- zene, toluene, xylene, ac€tone or similar compoundsbecausethey may damagethe plastic.

Lubrication

Componentsin this instrumentdo not requirelubri- cation.

Fixtures and Tools for Maintenance

Table 6-2 lists kits and fixtures that are availableto aid in servicingthe spectrumanalyzer.

Visual Inspection

After cleaning,carefully check the instrumentfor such defects as defectiveconnectionsand damaged parts. The remedyfor most visibledefectsis obvious. lf heat-damagedparts are discovered,try to determine the cause of overheatingbefore the damagedpart is replaced;othenwise,the damagemaybe rep€ated.

Transistor and Integrated Circuit Checks

All transistorsand integratedcircuitsare soldered on the boards to prevent pin contact problems, Periodic checks of the transistorsand integratedcir- cuits is not recommended.The bestmeasureof perfor- manceis the actualoperationof the componentin the circuit. In most cases any degradationin performance will be detectedby the microcomputerwhen it runs its power up routine. Performanceof thesecomponentsis also checkedduring the performancecheck or recali- bration;any sub-standardtransistorsor integratedcir- cuits will usuallybe detectedat thattime.

Whenhandlinga static-sensitive,observethe neces- sary handlingproceduresto preventdamage.

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6-2

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