Input Coupling

Signals applied to the input connector can be AC coupled, DC coupled, or internally disconnected from the input to the Vertical Input Amplifier circuits. When the Input Coupling switch S5 is set for DC coupling, the input signal is coupled directly to the Input Attenuator stage. When AC coupled, the input signal passes through capacitor C3. This capacitor prevents the DC component of the signal

^ Trigger

Generators

^ Trigger

Generators

Fig. 3-2. Detailed block diagram of the Channel 1 Preamplifier.

from passing to the amplifier. In the GND position, S5 opens the signal path and connects the input of the amplifier to ground. This provides a ground reference without the need to disconnect the applied signal from the input connector. Resistor R4, connected across the input coupling switch, allows C3 to be pre-charged in the ground position so that the trace remains on screen when switched to the AC position.

When a X10 probe with a scale factor switching connector is attached to the CH 1 OR X input connector, the base of Q382 is returned to ground through R381. Q382 is now biased into saturation and conducts current through X10 indicator DS382. The collector level of Q382 is very close to +5 volts; therefore, there is insufficient bias at the base of Q386 to cause it to conduct and X1 indicator DS386 remains dark.

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