XAxis Amplifier
In all positions of the TIME/DIV switches except X-Y, the input signal to the base of Q1224 will be the sawtooth waveforms from the sweep generators. In the X-Y mode however, the sweeps are disabled and the signal applied to Q1224 comes from the Channel 1 Preamp via the X-Axis Amplifier stage. This stage includes Q1214, Q1218, and their associated circuitry.
- X-AXIS SIGNAL FROM CH 1 PREAMP
Fig. 3-7. Detailed block diagram of the Horizontal Amplifier.
Fig. 3-7. Detailed block diagram of the Horizontal Amplifier.
Q1214 is connected as a feedback amplifier with R1214 as the feedback element. The input resistance is made up of R1211 and the gain-setting adjustment R1215. When not operating in the X-Y mode, the base of Q1214 rises toward the +15 volt supply but is clamped at approximately +5.7 volts by CR1216. This reverse biases the base-emitter junction of Q1214. The base of Q1218 also rises to approximately +5.7 volts. With the junction of R1202-R1219 sitting at approximately 0 volts, Q1218 is also biased off.
When the BEAM FIND pushbutton is pressed, R1249 is connected to ground. This reduces the current supplied through Q1244, which has the effect of shifting the operating level at the collector of Q1244 in the positive direction. This causes the Horizontal Amplifier to operate closer to the point where signal limiting occurs, thereby ensuring that an overscanned display will remain within the viewing area of the CRT.
When the TIME/DIV switches are set to the X-Y position (fully counterclockwise), —8 volts is applied to the junction of R1212 and R1217. Also, +5 volts is applied to the emitter circuit of Q1218 through CR1202. This biases the Z-Axis Amplifier circuit into conduction. At the same time, +5 volts is applied to the Channel 1 Scale-Factor Switching Amplifier circuit (through CR1201) and to pin 18 of the Sweep Control Integrated Circuit U870. This enables both scale-factor indicating circuits at the same time and disables sweep generation.
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