Circuit Description - Tektronix 067-0599-00 Instruction Manual

Section 3—067-0599-00
CIRCUIT DESCRIPTION
This section of the manual describes the circuitry in the 067-0599-00 Calibration Fixture. The description shows the
relationships between the stages in each major circuit. Circuits commonly used in the industry are not described in detail.
Schematics of all the major circuits are given in Section 8, Diagrams and Circuit Board Illustrations.
Schematic <» , Connectors to Indicator
Resistors R1 through R14 provide the maximum load the
576 power supplies might encounter with Standard Test
Fixtures. R13 and R14 simulate a load that might be en-
countered if a camera were used on the 576.
Schematic ® , Function Switching
The DISPLAY OFFSET MULTIPLIER, S105, is a preci-
sion voltage divider from an +11.7 V source. R102, 25 kQ,
sets the voltage precisely at the top of the divider. R105
consists of twenty 1 kQ resistors, matched to 0.02%. S105
allows selection of 21 different voltage levels to check the
display offset in the 576. S107, CALIBRATOR RANGE, se-
lects precise voltages for comparison with the calibrator
voltages within the 576. R109, R112, R115, and R118 allow
the adjustment of the 067-0599-00 calibrator voltages. For
the 50 mV CALIBRATOR RANGE position, a variable fea-
ture is provided with R121 being the variable pot in a divider
string consisting of R120, R121, and R122.
+1500 V from the Collector Supply in the 576 is applied
through S100, the FUNCTION switch. This +1000 V supply
is divided on S165, the HORIZONTAL VOLTS switch, into
+10 V. This +10 V is compared to a +10 V reference, de-
rived from the +11.7 V in the calibration fixture, and main-
tained through a regulator consisting of Q147 and the
integrated circuit U149. VR146 and VR147, tied from the
collector of Q147 to the 25 V supply, provide over-voltage
protection for Q147. The current from the +1500 V supply
passes through zener diodes VR138 through VR145 to the
collector of Q147, through R148, and finally, is referenced to
the chassis through U149. The output voltage of U149 is
maintained as a constant depending upon the differential
input voltage. This in turn changes the current through the
grounded base stage Q147 to maintain 10 volts at the junc-
tion of R165 and R167. The current through R167 must
pass through the other resistors in the voltage divider. This
maintains the selected voltage, at the junction selected, as a
precision voltage. There will, however, be additional current
through the remainder of the voltage divider. This current is
due to the attenuator resistors in the 576. The voltage at pin
"A" of the circuit may get as high as approximately 1100
volts at some positions of the switch. The .5, 1, 2, and 5 volt
base position get their voltages from the voltage divider on
the vertical switch schematic KS
Schematic , Step Generator Switch and
Pulse Generator
The Steps In signal to S210, the STEP GENERATOR
switch, is the Step Generator output from the 576 via the
STEP GENERATOR LOADS switch of the 067-0599-00.
The purpose of this switch is to provide a current load for
the current steps and a voltage divider in the voltage step
mode. Integrated circuit U230 is part of an operational am-
plifier whose purpose is to keep the voltage change of the
Steps Out constant when the voltage of the Steps In is
changed.
Q234 drives the Step Polarity Invert relay in the 576.
Q234 is turned on and off by contact 32 of the STEP GEN-
ERATOR SWITCH, S210.
Q241 and Q251 make up a free-running multivibrator
whose period is set to 200 us by R244. The output of the
multivibrator is applied through R255 to the base of Q256
and amplified to produce a +25 V pulse. This +25 V pulse
is then divided by R258, R259, and R260, producing a
+0.5 V pulse. R259 allows exact adjustment of +0.5 V
pulse amplitude. The output of the multivibrator is also ac
coupled via C262 to Q264 and Q268, a ramp generator
whose time constant is controlled by R268 and C270. The
ramp is output through source follower, Q271. R275 pro-
vides adjustment to an exact +0.5 V sweep amplitude.
Schematic ® , Vertical Switch
The 115 V ac line voltage is applied through the intercon-
necting box of the 067-0599-00 to the primary of T301, rec-
tified, and filtered by CR302, CR303, and CR304. Q305 is a
series regulator for the +25 V supply. Q308 and Q307 form
a comparator circuit, using the +25 V regulated supply.
VR310 provides a reference for the +11.7 V supply,
from which a +10 V supply is derived, adjustable by R311
and R312. An operational amplifier, formed by Q320, Q322,
Q324, and U327, controls an error amplifier formed by
Q332, Q335, Q337, and Q340. From the emitter of Q340 an
error signal is fed back to the gate of Q320 in the opera-
tional amplifier to keep a constant +10 V across the resis-
tors selected by the VERTICAL switch, S360. Seven
3-1