XY Amplifier

When the X-Y display mode is selected using the SEC/ DIV switch, the XY signal line goes LO and XY Switch transistor Q720 is biased off. The XY signal is also applied to FET Q714 (used as a switch to prevent crosstalk) in the XY Amplifier to bias it on. With this action, the XY Amplifier is enabled to pass X-Axis signals on to the Horizontal Preamplifier. Another function of the XY signal is to disable the Sweep Generator to prevent the Sweep signal from being applied to the Horizontal Preamplifier.

The X-Axis signal is derived from the Channel 1 internal trigger signal and applied to the base of Q703. Transistor

HORIZONTAL

POSITION

R726

FROM SWEEP GENERATOR

FROM A SEC/DIV XY SWITCH

FROM INTERNAL X-AXIS SIC TRIGGER AMPL

MAGNIFIER

HORIZ

PREAMP

Q730

_».

Q731

Q736

FROM A SEC/DIV XY SWITCH

FROM INTERNAL X-AXIS SIC TRIGGER AMPL

XY

AMPL

Q703

, Q706

Q708

» Q7M

FROM Z-AXIS AMPL

BEAM FIND

MAGNIFIER

Deflection Loupes
TO CRT v HORIZONTAL ' DEFLECTION PLATES

3827-17

Figure 3-7. Detailed block diagram of the Horizontal Amplifier.

Q703 is one-half of a differential amplifier composed of Q703 and Q706. The base of Q706 is referenced to ground through R706. Transistor Q708 amplifies the output signal from the collector of Q706 and applies it to the drain of FET Q714. A feedback network composed of R709, R708, and C708 is connected between the collector of Q708 and the base of Q703. The feedback network sets the overall gain of the X Y Amplifier, with X-Gain potentiometer R709 adjustable to obtain the exact gain required.

The X-Axis signal passes through FET Q714 and is applied to the base of Q731 in the Horizontal Preamplifier. Horizontal positioning current on the base of Q730 is added to the X-Axis signal by the action of the differential amplifier. Then the sum of these two currents is amplified by Q736 and applied to the input of the Horizontal Output Amplifier.

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