Tektronix 494AP service manual Diagnostics, Troubleshooting Using Theerrormessagedisplay

Diagnostic Firmware

The firmware in the sp€ctrum analyzer provldes diagnosticroutinesthat can be usedwittritre Diagnostic part of this sectionto troubl€shootth€ FrequencyCon- trol systemand diagnosepower Supplyproblems.This part fottows GenErat trouOtestrbttini information. Refer to this part to help isolate probljms withinthis !9op. Th9 foilowingare atso some g€neratsuggestions that mayhelpisolatea problemwhentroubleshooting.

Troubleshooting Steps

1.Ensurethat the problem exists in the spectrum analyzer by checking the operation of associaiedtest equipment.

2.Try to isolate the problem to a circuit or at l€ast board level by evaluating operationaf symptoms; for example,absenceof the fr€quencydot coutObe caused by a malfunctionin the video summing stage, the markergenerator,or switchingcircuits.

3.Three levelsof block diagramsare providedto aid in understandingthe theory of operation.The most detailedlevel is adiacentto the schematicand usually provides signal and voltage tevels at critical pointi within the circuits. Signallevels are usuallytheievels requiredto producefull screendeflEction.

4. lnstructionson how to remov€or replacethose assemblieswhich are not obvious,are providedin this section. Referto this part before removingany assem_ bly for testingor repairing.

Matntenance- 494A,1494ApServiceVot. 1

_ _5. Visuallyinspect the area or assemblyfor such defects as broken or loose connections, improperty connected components, overheated or burned com_ ponents,chafed insulation,etc. Repair or replaceall obvious defects. In the case of overheated com_ ponents,try to deterrninethe cause of the overheated conditionand correctbeforeapplyingpower.

6.Use successiveelectricalchecks to try to locate the problem. An oscilloscopeis a valuablet€st itemfor evaluatingcircuit performance.lf appticable,checkthe ca-librationadiustments; howEver, before changing an adjustmentnote its position so it can be retumed tb its originalsetting. This will facilitaterecalibrationafter the trouble has been locatedand repaired.

7.Dotermine the extent of the repair needed; if complex, we recommend contacting your local Tek_

tronix FieldOfficeor repres€ntative.lf minor.suchas a componentreplacement,see the Replaceableparts list for replacementinformation.Removaland replacement procedureof the assembliesand sub-assembliesaredescribedunderCorrectiveMaintenanc€.

When measuringvoltagesand waveforms,

useextr€mecare with the placementof test probes. Becausesomecircuitboardshave

ahigh componentdensity,accessto points in some circuits is limited. A test prob€ could accidentallyshort a circuit and gen- erate transient voltages that can destroy manystatic-sensitivecomponents.

DIAGNOSTICS

This part consistsof explanationsand procedures for troubleshootingthe freguencycontrol systemand the powersupplyusingdiagnosticfirmwarein the spec_ trum analyzer.

TROUBLESHOOTING USING

THEERRORMESSAGEDISPLAY

Introduction

This part containsproceduresfor troubleshooting thefrequencycontrolsystemandthEpowersupply.

Whenth€ microprocessordetectsa failureor error in the FrequencyControlloopsor a failurein the power Supplyvoltagesit will cause the spectrumanalyzerto displayan error messagenear centerscreenfor a few seconds;this is followed by an error status message nearth€ top of the screenwhiehrernainsas longas the error or problernexists.

These error messages pertain to problems that exist under current instrumentoperationalmodes or front panelsettings;for example,an error that pertains to the hardwarein the phase lock loop will exist only when thE instrumentis in the phase lock mode (nar- rowerspan/divsettings).

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