Tektronix 1710J Series, Instruction Manual

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Theory of Operation
1710J-Series Waveform Monitors
5–11
The composite sync signal also drives the vertical sync generator. The SYNC
SIG is integrated by R947, C950, and U947A. During normal video lines and
vertical serrated lines, the signal is mostly positive and charges the capacitor,
C950, holding the output of U947A negative. During the vertical broad pulses
the signal is mostly zero and the capacitor discharges making the output of
U947A go positive. The output then swings negative again after the broad
pulses.
R850 and R751 offset the output of U947, which drives a comparator, U753B,
through C853. U753B shapes the FIELD signal to the TTL level required to
drive the microcontroller (Diagram 5) Interrupt 0 input. The voltage divider
formed by R850 and R751 also provides a 2.5 V source for the end of sweep
comparators in the sweep generator on Diagram 4.
U252 is a transistor array with two of the transistors connected as a differential
current switch. The static output level (pin 8) is set by the front-panel INTENS
control using Q243 (in the focus control) as a current source. The blanking signal
is input to the transistor switching array through U252B (pin 9). When it goes
high, the current output, collector of U252A (pin 8), is shut off and the Z-axis
amplifier (Diagram 8) blanks the CRT.
Trace rotation compensates for changes in the magnetic field surrounding the
1710J-Series Waveform Monitor. Q142 and Q143 are emitter followers to
provide trace rotation current to the CRT surrounding coil located inside the CRT
shield. Amplitude and polarity are controlled by the front-panel ROTATE
screwdriver adjustment.
U263A is a triangle generator whose output is compared to the front-panel
SCALE control output level, by U263B (a comparator). Whenever the output of
U263A is higher than the level from the front-panel SCALE control, Q158 is
turned on and current is drawn through the bulbs (DS100, DS200, and DS300) to
ground. The duty cycle of Q158 is determined by the level set by the front-panel
SCALE control.
The + and –15 V supplies generated by the main low voltage power supply are
further regulated to meet the power requirements of the Main (A3) circuit board.
U164 is the regulator; its reference level is set by R167, the –11.8 V adjust.
U172 is the +11.8 V supply regulator and its reference level is set by R168, the
+11.8 V adjust.
Vertical Sync Generator
Z-Axis Control
Trace Rotation
Graticule Illumination
Regulators