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Theory of Operation
1780R-Series Service Manual
3–75
Diagram 29 XY Inputs & PIX Monitor
Picture monitor sweeps and XY input signals drive the Deflection Amplifiers
through switching circuits on the Deflection Amplifier schematic diagram. The
Sweep Generators have sufficient gain range to accommodate either 525/60 or
625/50 scanning rates. The XY Amplifiers are designed for 0 to +12 dBm audio
signals, but can be internal jumper switched to provide approximately X10
Amplifiers for non-audio applications.
Picture Monitor Horizontal Sweep. Q602 is turned on by H rate sync to start
U506A, which is a J-FET input operational amplifier configured as a Ramp
Generator. Ramp slope is dictated by C503; ramp amplitude is adjusted by R604
(Horizontal Gain). U506B is connected as an inverting operational amplifier,
with a gain of approximately 2. A small amount of vertical signal is input to the
non-inverting input of the operational amplifier for orthogonality adjustment
purposes. R606 (Pix Horiz Pos) provides a limited amount DC offset adjustment
that is used for horizontal positioning.
Picture Monitor Vertical Sweep. Q403 is turned on by V rate sync to start U506D,
which is a J-FET input operational amplifier configured as a Ramp Generator.
Ramp slope is dictated by C401; ramp amplitude is adjusted by R404 (Vertical
Gain). U506C is connected as a non-inverting operational amplifier, with a gain
of approximately 1.5. R407 (Pix Vert Pos) provides a limited amount DC offset
adjustment for vertical positioning.
Overview
Circuit Theory