Tektronix 494AP service manual C3026, C2016, Filtercomponentcombinations, DB2 DB3

Theory of Operation- 4g4A/4g4ApServtce,Vol. 1

EXTVIDEOSELECT

MARKER/VIDEO15

VIDEO FILTER

OUT

6 , 1 1

INTERNAL VIDEO

RC FILTER u20158

OATA BIT 1

Flgure 7-14.Simplllied diagram of a video filter.

Tabte7-6

FILTERCOMPONENTCOMBINATIONS

Bandwldth	DB2	DB3	DB4	R2023	c3026	R2021	R2022	c2016
30 kHz	0	0	0	X	X	X	X
3 kHz	0	0	't	X	x	X
300Hz	0	1	1	X	X	x
30 Hz	1	0	0	X	X		X	X
3 H z	I	0	1	X	X	x	x	X
0.3Hz	1	1	1	X	X	X

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Two signal inputs (EXT MARKER/VDEO)can be appliedto the videofilter circuits. ThE EXTViOeOsig- nal, from the rear-panelMARKERIVIDEOconnector.is appliedto pin 15 of switchU306gAthroughedge con_ nector pin 53. The INTLVTDEOsignal,from the Video Amplifiercircuits(via the front-panelLOGCAL control), is appliedto pin 2 of U3063Athroughedge connector pin 51. Note that the internalvideo sectidnsof switch U30634are normallyheld energized(pins 2 and three connected,pins 15 and 14 disconnected)by the +5V supprythroughR3064. tf the EXTvtDEo sELECTtine (from the rear panel ACCESSORIESTNTERFACEcon- nector,throughedgeconnectorpin 55)is grounded,the externalvideosectionsof UO063Aare de-energized.

Wh€n this occurs, the EXT VIDEO signal is applied through, or around, the filter to becorneth€ VIDEO FILTEROUT signal at edge connectorpin 57. This is shown in the simplifiedschematicdiagramof Figure7- 14 .

As shown in Figure 7-14, when no tiltering is selected(alldatabits are 0), eitherthe internalor exter- nal signalis routedthroughU3062and aroundthe filter, becausethe two sections of U30638 are selectedby DBl. WhenDB1 is high, the videois routedthrough the filter. Somefilter valuewill be setectedby bits 2, 3, and 4. Thesedata bits controlthreesectionsof switch U20158to add or deletefiltertime constants.

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7-38

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