Tektronix T921 User Manual

SEC/DIV
switch setting . Chopped mode is obtained for
sweep speeds of 1 ms and slower ; alternate mode is
obtained for sweep speeds of 0 .5 ms and faster .
In the DUAL TRACE
mode CR4360 and
CR4361
are
forward biased so that pins 10 and
13 of U4364B are
HI .
This allows U4364B to change state upon arrival of a clock
pulse .
In the chopped mode, pin 1 of U4376A is ungrounded,
allowing the multivibrator, U4376A and U4376B, to free
run at about 500kHz . The output
at
pin 11
of U4376D
serves as a clock pulse for U4364B . The state of U4364B
changes on each negative transition of U4376D pin 11 .
Pins 8 and 9 of U4364B switch the diode gates at a 250 kHz
rate .
The clockpulse is also fed to U4364A which provides an
output pulse to the Z-axis amplifier to blank out the
transitions between channel 1 and channel 2 traces .
U4364A, U4376C and associated components form a one-
shot . If pin 1 of U4364A goes LO, the output pin 5 is set LO,
causing pin 8 of U4376C to go HI . This in turn causes pin 1
of U4364A to go HI after being delayed by C4386 charging
through R4386 .
The clock pulse applied to pin 3 of U4364A causes pin
5 to go HI, which, after inversion and some delay, moves
pin 1 LO again . This causes pin 5 to go LO again . The
positive-going voltage pulse (whose width is determined
by R4386 and C4386) is converted to
current
by R4385 and
sent to the Z-axis amplifier to blank switching transients
.
In the alternate mode, pin 1 of U4376A is grounded,
preventing multivibrator operation, thus keeping pin 12 of
U4376D HI . At the end of each
sweep,
the
base of
04372
receives a current pulse driving it into saturation . The
resulting negative-going pulse at the collector is fed
through C4372 to pin 13 of U4376D, causing pin 11 to go
HI . This in turn switches U4364B to pass either channel 1
or
channel 2
to
the
delay
line
driver at the end of each
sweep . Pin 2 of U4364A is grounded through the SEC/DIV
switch and prevents an output at pin 5 .
For a discussion of the Delay Line and the Delay Line
Driver circuits, refer to the Circuit Description section of
this manual .
Trigger Pickoff : The Vertical
Mode switch also selects
the appropriate internal triggering source for channel 1
and channel 2 . With the Vertical Mode switch set to CH 1,
DUAL
TRACE, or DIFF, CR4364 is forward biased and the
signal from the channel 1 trigger pickoff
goes to
the sweep
circuit . In these modes, CR4362 is connected to -8 volts,
thus reverse biasing CR4366, preventing the channel 2
trigger signal from entering the trigger input amplifier .
With the Vertical Mode switch set to CH
2, CR4366
becomes forward biased
while CR4364 is reverse biased,
because
CR4363
is
now connected to -8 volts . Refer to the
Circuit Description section of this manual for a discussion
of the rest of the Trigger Pickoff circuitry, which is
common to all versions of the T922 or T922R .
CMRR PERFORMANCE CHECK
(Perform after Step 7 of Section 3,
PERFORMANCE CHECK)
Equipment Required
(See Table 3-1 in Section 3 of
this manual for equipment
specifications and recommended types .)
1 . Sine-Wave Generator
2 . 50 0 BNC Cable
3 . 50 0 BNC Termination
4 . 50 0 BNC Dual-Input Coupler
Equipment Setup
Procedure
1 . Set : Vertical Mode

CH 1
CH 1 and CH 2
VOLTS/DIV

5 mV
CH 1 and CH 2
AC-GND-DC AC
SOURCE INT
MODE AUTO
3 . Set Vertical Mode to DIFF .
Options-T 92 1 /T922/T922R
Connect the sine-wave generator to the CH 1 and CH 2
inputs via a 50 0 bnc cable, 50 f2 bnc termination, and
dual-input coupler .
2 ; Set generator to 50 kHz . Adjust generator for a six-
division display .
4 . Adjust one of the VAR VOLTS/DIV controls
for
minimum vertical
deflection (best CMRR) .
5 . Without readjusting generator amplitude,
set
generator frequency to 5 MHz .
6 . CHECK-Vertical deflection is 0 .6 division or
less .
Option 1 Page 3

Tektronix T921 Specifications

General

Brand	Tektronix
Model	T921
Category	Test Equipment
Language	English