General - Motorola R-2001A Service Manual

8-1. General. The Scope Amplifier module contains the horizontal and vertical deflection amps, the
horizontal timebase generator, focus and intensity control circuitry, and miscellaneous CRT bias adjustments.
A block diagram of the Scope Amplifier module is shown in figure 8-1 with its schematic shown in figure 8-2.
8-2. Deflection Amplifiers. The vertical and horizontal deflection amplifiers are identical. The input signal is
initially amplified and split into two signals 180° out of phase. Each of the two signals is then further amplified
to become the CRT deflection plate signals. The amplifiers provide up to 200 volts peak-peak signal capability
with a 1 MHz frequency bandwidth.
8-3. Horizontal Timebase Generator. The horizontal timebase generator provides calibrated sweep rates
over a six decade range from 111 sec to 100 msec per division. Sweep rate selection is from the processor via
the SCOPE SWP CONT 0-7 signal lines. Veriner control over the sweep rate is via the SWP VERN VOLT input
from the front panel. Sweep triggering is either the auto or normal mode as selected by the AUTO/NOR TRIG
SEL line from the front panel. In the auto mode if the SYNC PRESENT input is high indicating no sync, the
scope sweep is self triggered after a hold off time. If there is a sync present, the sweep will wait for a pulse on the
TRIG PULSE line to start the sweep after the hold off time. For the normal trigger mode the sweep will always
wait for a TRIG PULSE input.
8-4. A sweep cycle consists of two parts, the sweep and the hold off. During the sweep the CRT is unblanked
via the SWP BLANKING line and the horizontal trace is made. At the end of the sweep the CRT is blanked and
the hold off time begins. During the hold off time, which is equal to the sweep time, the sweep generator and
trigger circuits are reset in preparation for the next sweep.
8-5. Horizontal Switching. The input to the horizontal deflection amp is selected between two sources. The
INT HORIZ IN signal line provides the horizontal character sweep and the horizontal spectrum analyzer
sweep. The other source is the scope mode signal path from the horizontal positioning suming amp. The scope
mode signal is either the output of the Horizontal Timebase Generator or the EXT HORIZ INPUT from the front
panel. Selection between internal horizontal and scope mode horizontal inputs is via the SCOPE MODE EN
line from the processor. Selection between the two scope mode signals is via the EXT HORIZ EN line.
8-6. Intensity Control. A crossover network is used to provide CRT Z-axis modulation from DC to 1 MHz.
The INTEN LVL signal from the front panel control is gated with the SCOPE Z-AXIS signal by the Intensity
Level Gate. The gated signal is sumed with the HV REF and INTEN SMPL VOLT signals to provide the INTEN
TV signal. The INTEN TV (Intensity Tracking Voltage) is the low frequency control path which drives the
intensity optoisolator in the High Voltage Supply.
8-7. The high frequency modulation path is via the Z-Axis Modulator circuit, line. line. The resulting CRT Z-
AXIS signal is capacitively coupled to the CRT grid.
8-8. Focus Control. The FOCUS TV (Focus Tracking Voltage) signal is obtained by comparing the FOCUS
LEVEL control line to the FOCUS SAMPLE VOLT signal. The tracking voltage signal drives an optoisolator
circuit in the High Voltage Supply which controls the CRT focus voltage.
8-9. Astigmatism, Geometry, and Trace Rotation. These three CRT alignment controls are obtained from
the respective wipers of three potentiometers. Each potentiometer is connected between supply voltages
equal to the adjustment range required.
SECTION 8
SCOPE AMPLIFIER (A2)
8-1