Tektronix 494AP DEFLECTIONAMpLtFtERSDiagram27, digitalstoragesweep positions. The resulting

o o o

t	the 500 digitalstoragesweep positions. The resulting
o	clisplayappearsas a bright dot sweepingacross the
t	crt, risingandfallingwith the signat.
t		The basic circuits consist				of a set of latches,a
o	digital-to-analog
			convert€r,a compar"toi, pulsegen_
o	erator,and controlcircuitry.The							"
							HorizontatDisptay[iD)
	data representsthE ligital equivatentot the pi"ieni
a	update position.The latches cipture the data, and the
	digital-to-analogconverter{dac) converts it, creating
:	the analog horizontal deflection signat. When the
t	swe€p		voltagereaches-
				the dac level,-thesw€ep stops
	for a longer period of time, and thereforethe crt is
o	brighter,than at other sweep positions. On the next
	sweep,the HD data increments
o	rnoving						to the next position,
			the cursoralongthe sweep.
o
I	... Th"		DSPLEN (DisptayEnabte)signalctocks
								the HD
	(Horizontat
a			Oata)signatsinto latctres'Ul020
	The tatchoutputsdrive U2020,							and U2O3O.
	converter.The converter's				a 1O_bitoilitat+o_anatog
o				output currenidrivesoperai
	tional amplifier U4029A, producing,a voltage called
3	HORIZStG. Whena digitatstoragJsignat
	HORIZSIGdrivesthe horizontat							is disptayed,
a						O-eReciionnmpliiier.
o	.	Also,U196-OcomparesHORIZStGto the sweepvol-
a	tage from U40Z9B. The comparator output drives the
	"Updat€lnt€nsity.input on the MarkertC, U30eO*re.
o	tularkertC Aenerates				putse,
			"	l-6_-g!it				ctocied by DSpL
a			edge of U3O2O';
	5N..Ll"_-ri:'.!g					output putseproduces
	the INTENSITysignalthat temporaiilypreventscount-
t	ing by the g-bitdisplay counter							'in
								u5020. This
	effectivelystopsthe beamfor a shorttimeanclcausesa
o	bright.spot (cursor)on			the trace to indicatethe horizon-
o	tal pointbeingupdated.
o
o		Fast Retace Blanking.Between
o							the displayof the
	B memorycontentsand displayof the A m€morycon-
o	tents,a fast retraceoccurs,This retrace,
								unlikethe one
	that tollows the A memory display (cursor),is not
o	requiredto be seen and is blanke;. This is accom-
I	plishedby btankingcontrol flip_flopU10148,which is
	controll€dby the most significantbit of the rnemory
o	addressandthe DSPLEN signatduringa markercycte.
a
o	. .	MernorieaIntegrated.circuitsU1026andU2026pro-
o	vide 8k bits of randomaccess m€moryfor storageof
	tfie 1000data pointsusedIn the digitalitoragesystem.
o	Addressingduringbus transferof iremory datais con-
	trolfed by addresstri-state buffers Ul}dg and U1016
o	and by horizontalcontrol lC				U2095 during memory
o	update.
a
o

o o

Theoryof Operaton - 4g4[l4g4fupService,Vol. 1

DEFLECTIONAMpLtFtERS(Diagram27)

Referto the btock diagramadjacentto Diagram27 as well as the schematic diagram. The Deflection Amplifierreceivesverticalsignal informationfrom the verticalsectionof DigitalStorageor the Mdeo proces_ sor, and horizontalor sweepvoltagefrom the horizontal sectionof DigitalStorageor the Sweepboard. Readout data for the display comes from the crt Readoutcir- cuits. Th€ output of the D€fl€ctionAmplifierdrives the crt deflectionplates. The amplifierscontainthe switch- ing circuits necessaryto performth€ setectionfunctions and they also contain the amplifierstages neededto producethe deftectionplatedrivesignats.

Horizontal Section

SignaltinesHORTZONTALStcNAL (fromthe digitat-and storage circuits through edge connector pin ag) SWEEP(tromthe Sweepcircuitthroughedgeconnector

pin 51) are appliedto switchlC UZOSSAUZ0SS. unOer. control of the STORAGEOFF signal (from the digital storagecircuitsthroughedge connectorpin 7), setects eitherthe HORIZONTALSTGNALor SWEEpinput.The SWEEPsignatis setectedwh€n the STORAGEbff tine is floatingor puttedhigh. The HORTZONTALSTGNALis selectedwhen the line is pulledlow. Resistivedivider R7051 and R7081 reduces the selectedsignal from 1 V/divto 0.5V/div. UZIT! buffersthe selectLdsignat. It goes out to the HORIZOUTrear-panelconnectorvia edge connectorpin 48. UZoZ3appliesthe signatto switch U70558. The HORTZR/O signat,lrom the Crt Readoutcircuits,is also appliedto U7OS5B.The R/O OFF signal, from the Crt Readout circuits selects betweenth€s€ two signals. WhenR/O OFF is floating or pulled high, the switch transmitsthe signal from bufferU7073to the shaper. Whenthe lineis pulledlow, it selectsthe HORTZONTALR/O signal.

U70558appliesthe signalto a shapernetworkto comp€nsate tor non-linearityin the crt deflection characteristics. This network consists of resistors R5059,R5058,R5057,RS062,R4061,and R4059,ptus diodesCR1012,CR4051,CR4OS8,and CR4056.The HORIZONTALPOSITONvottage,from the front panet via edge connectorpin 47, throughresistor R6032,is appliedto the shaper circuit so the shape correction factorrelatesto the crt deflection.

The shaped signal is then applied through preamplifierU2060 to the deftectionamplifiercircuits. HorizGainadjustmentRl0S5, calibratesth€ amountof gain compensationrequiredfor properdeflectionsensi- tivity.

The horizontald€flectionamplitierconsistsof two circuits similarto each other, one for each horizontal deflectionplate. Onecircuitis an invertingamplifier,the otheroperatesin-phase.Inputsto e4oggAof the invert-

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