Tektronix 1710J Series, Instruction Manual

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Theory of Operation
1710J-Series Waveform Monitors
5–13
If there is no H or V trigger, the output of the running sweep generator is self
retriggered. When the ramp amplitude reaches about 3/4 of its maximum
amplitude U445B trips and sets the flip-flop preset high to turn on Q451 or Q450
to start retrace. Just before retrace begins U445A also trips and pulls the flip-flop
clear high to lock out the trigger signal and generate the HOLDOFF signal used
by the timing generator (Diagram 3) to phase up the horizontal timing of the
input or filter switching.
An operational amplifier consisting of U564C and D and Q566 positions and
magnifies the sweep signal. R557 and R558 are the central elements of the
feedback resistor network. The value of the network is altered by R552 (1
m
s cal)
and R553 (0.2
m
s cal) when magnified sweep rates are selected. The junction of
input resistance (R559) and the feedback resistance network (R557 and R558) is
the amplifier input summing junction.
Horizontal positioning voltage is input to an operational amplifier, U655B,
which drives the mag amplifier summing point (along with the RGB staircase
signal, when RGB/YRGB operation is selected). The length of the sweep, in
RGB mode, is set by jumper J456 to accommodate either three- or four-step
sweeps (for RGB and YRGB modes).
U465A and U465B are comparators used to sense when the output of the
magnifier and position amplifier have driven the CRT beam to the edge of the
CRT screen. When the beam is horizontally overdriven, the input to U234C is
pulled low to generate the BLANK enabling level for the Z-axis amplifier
(Diagram 3).
The horizontal output amplifier is composed of Q858, Q860, Q862, and Q864,
with Q868 and Q865 serving as current source. R960 provides the differential
mode feedback; R958 and R959 provide the common mode feedback that biases
the outputs to approximately 50 volts. The gain of the amplifier is determined by
a voltage divider with two adjustments, R660 (sweep length adj.), and magnified
sweep registration R661 (mag registration adj.).
Microcontroller, Diagram 5
The microcontroller is the brain of the 1710J-Series Waveform Monitor. It
monitors the front panel, and reacts to changes to any switch setting and
generates appropriate control levels for circuits in the rest of the monitor.
The microcontroller interfaces the front-panel switching to the 1710J-Series
Waveform Monitor control functions. The programmability and integration of
RAM, ROM, and counters provides flexible control over the complex switching
required for this waveform monitor. The microprocessor is equipped with
Magnifier Amplifier
Horizontal Output
Amplifier
Processor