Marconi-2955-replacement-osc-v2 电路图.pdf

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1、TheMarconicommunicationtestset2955serieshasa commonfaultthe10MHzoscillatorisproneto failure.Showsasabreakingupofthedisplayand generallockup.Itisnotagoodideatouseyourunitif itisshowingthissymptomasitcancorruptthe eeprom,seebelowhereisonewaytofixit. CourtesyBobBlumfeldsVK6JBN deMarkWebsterVK2BAK Thefa

2、ultyoumentionsoundslikethe10mhzrefoscillatoronthecrtboardis intermittent.Thisisanextremelycommonfault. Itsasmallgreyboxlocatedtowardstherearofthelongcrtpcb.Thereisa bluemultiturnpotdirectlyaboveit.Thatsetsthefrequency.Itwilllockthe unitupifitfailsduringwarmuporoperation.Itsuppliesallthetimingsignals

3、 forthe2955includingthedisplay.Bestwaytofixitisremoveandinstallanew 10mhzreferenceoscillator.Theoriginaloscillatorisnoteasilysourcedand theyaregettingtooold.Ifitteda10mhzVectronovenwhichfitsnicelyonto thesideofthecasedirectlybehindthecrtpcb.Thereis12vonthecrtboardas theoriginalovenuses5v.Youwillrequ

4、ireatransistor,acoupleofresistorsand acapto“pullup”theleveloftheoscillatorsignalto2vppwhichtheMarconi needstowork.Ifthelevelislowthentheunitwontstartonpowerup.You wontobviouslyneedtodothatifyousourceanovenwithahighleveloutput. Isupposeanotherwayistofindagoodhposcillatoronebay. Alsodontusetheunittooo

5、ftenastheintermittenttimingsignalswillscrew thecaldataintheeepromandyouwillneedanewboard.Symptomsofthatis unusualreadingsinthesinad,frequencyetcwhennosignalsareapplied.Also levelsoutwillbeunusualtoo!ThishappenedtoanothersetIfixedupandI endedupbuyingasecondhandcontrollerboardtofixit.emailtoVK2BAK Rad

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7、CH1 :CH2 : Note : DATE = 30/05/2007 TIME = 17:14:20 SAMPLING RATE = 100MS/s TIME DIV = 50 nS/div CH1 VOLT DIV = 2V/div Input Coupling = DC TEST REPORT DSO-2100 USB CH1 :CH2 : Note : DATE = 30/05/2007 TIME = 17:13:40 SAMPLING RATE = 100MS/s TIME DIV = 50 nS/div CH1 VOLT DIV = 2V/div Input Coupling = DC