Main Interface - Tektronix 7704A Instruction Manual

square wave. The negative-going pulses have no effect on
01011. The positive-going pulses turn on Q1011 to
produce negative-going pulses at its collector, which are of
sufficient level and amplitude to drive the Clock input of
U1010.
U1010 is a triggered set-clear (J-K) flip-flop connected as
a triggered (toggle) flip-flop. The negative-going pulses from
Q1011 trigger U1010 so that the outputs change state with
each negative input pulse to provide a one-kilohertz output.
Output Amplifier
The one-kilohertz output of the Calibrator Countdown
stage is connected through Q1021 and 01023 to control
the conduction of Q1025 and 01027. Transistors 01025
and Q1027 are connected as a comparator. The reference
level at the base of Q1027 is determined by the network
R1037-R1039-R1038-R1034-R1035-01031. The 0.4 Volts
adjustment, R1037, is set to provide accurate output
voltage at the 0.4 V Calibrator pin-jack. The voltage at the
collector of 01027 changes at a one-kilohertz repetition
rate between zero volt and a level established by the
reference level at its base.
Output Voltage Divider
The output voltage divider, made up of resistors R1043
through R1058, is designed to provide a low-impedance
output for all ranges except 40 V, while providing accurate
output voltages between four millivolts and 40 volts.
(Four-millivolt and 40-volt outputs are available on internal
circuit-board pins.)
The output resistance at the 40 V pin is about 15
kilohms, as determined by R1041 and the equivalent
resistance of the divider network. The remaining output
voltages are accurate with a one-megohm load or, at
reduced output, a 50-ohm load.
Circuit Description—7704A Service
Switch Logic
The VERTICAL MODE and HORIZONTAL MODE
switches determine the operating mode of the Vertical
Interface
and Horizontal
Interface circuits
respectively.
Each
of these switches
is self-canceling;
i.e., only
one
button can be pressed at a time. Specific operation of these
switches is described
in connection
with the circuits they
control.
Indicator Lights
The indicator lights shown in connection with the mode
switches indicate which mode has been selected. When one
of the pushbuttons is pressed, it completes the circuit
between the associated bulb and the +5-Volt Lights supply.
A separate bulb is used for each mode switch pushbutton.
The A and B.TRIGGER SOURCE switches are also
illuminated to indicate the trigger source, but only one bulb
is used for each switch assembly. Light guides are used, so
that the button pressed receives light, but the remaining
buttons are not illuminated. The power for the indicator
lights is controlled by the rear-panel CONTROL ILLUM
switch (shown on diagram 9).
MAIN INTERFACEC2>
OUTPUT AMPLIFIER
Qloz2i-Qloz3
Ql025 - QIOZ7
2-kHz
OSCILLATOR
QIOO! - QIOO3
CALIBRATOR
COUNTDOWN
Qiofl - YIOIO
Qio3i
OUTPUT |
VOLTAGE |
DIVIDER
Fig. 2-2. Calibrator circuit detailed block diagram.