Tektronix 485 User Manual

c. Set B TIME/DIV to 0.1 ns, and set DTP to approxi
mately 0.00 to align the beginning of the A and B sweeps.
d. Adjust Cl 248 (above the relay in B Sweep) so that B
Sweep matches A Sweep timing on screen.
27. ADJUST 1 jus TIM ING A and B, CHECK 1 jus
DELAY LINEARITY
a. Set A and B TIME/DIV to 1 ns and 0.1 ns; time
marks to 1 ns; HORIZ DISPLAY to ALT.
b. Trigger A on the + SLOPE of the time marks.
c. Set the DTP dial to exactly 0.95. With the POSITION
(HORIZ), set the leading edge of the B display to a
reference position while keeping the first 10 markers of A
display on the screen. The intensified zone of A must start
on the second time mark.
d. Set the DTP to exactly 8.95.
e. Adjust C877 (located in front of the relay on the
lower half of the Sweep board) to move the B display to
the reference position of step b. The intensified zone of A
must start on the tenth time mark.
f. Repeat steps b through e for identical B display at the
two DTP dial settings.
g. Check the delay linearity by setting dial to exactly
4.95. The marker on the B display must be within 0.15 div
of the reference position.
h. Set B TIME/DIV to 1 jus; HORIZ DISPLAY to B and
the DTP dial to 0.00.
i. Adjust Cl 242 (located below the relay on the upper
half of the Sweep board) for one time mark per division
and for exactly 1 to 9 timing (center 8 divisions).
28. ADJUST A SWEEP LINEARITY (R863)
a. Set the 485 for a 20 ns/div AUTO TRIG Sweep with
the A TRIGGER HOLDOFF at max (but not B ENDS A).
b. Connect the 485 A GATE (rear panel) to the Ext
Trigger Input of the test oscilloscope using a 50 £2
termination at the test oscilloscope. Also, set the test
Calibration—485/R485 Service
oscilloscope to 20 ns/div and trigger it on the + SLOPE of
the 485 A GATE.
c. Connect the test oscilloscope 10X probe (10 MS2) to
the IN test point located near the center of the Sweep
board. Make the probe ground connection at one of the
GND test points on the Sweep board. Set test oscilloscope
Volts/Div for a probe tip deflection factor of 50 mV/div.
d. This display of the A sweep generator input, consists
of a positive step having overshoot followed by a positive
going linear ramp.
e. Adjust R863, (located below and in front of the
lower relay on the Sweep board) to extend the ramp at the
right of the display as linearly as possible back towards the
step at the left. Ringing should be minimized, except for
one overshoot cycle at the step.
f. Switch the 485 to 10 ns; the step and ramp ampli
tudes will increase. Make further adjustment if necessary to
optimize the 'linear ramp" on the two sweep speeds
(10 ns/div and 20 ns/div).
29. ADJUST 5 ns TIMING
a. Connect 5 ns time markers from H.F. Selector Out
put to CH 1 input;connect 50 ns time marks to EXT TRIG
INPUT; A TRIG SOURCE to EXT; A TIME/DIV to 5 ns;
then center trace (If using a 2901 Time Mark Generator,
set Trigger Out for 0.1 ns).
b. Adjust Cl 190, (located between Q1168 and Q1172
on B Trigger board) for one time mark per division and for
exactly 1 to 9 timing (center 8 divisions).
30. ADJUST 2 ns LINEARITY and TIMING
a. Set A TIME/DIV to 2 ns; select 2 ns time marks from
the Time-Mark Generator.
b. With the POSITION (HORIZ) control keep the peak
of one time mark positioned to center screen. Adjust
C1364, (located in front of H GAIN pot on Sweep board)
for most symmetrical timing (best linearity) of the sweep
over the center 8 graticule divisions.
c. Adjust R1226, (located above the relay on the lower
half of the Sweep board) for one time mark per division
and for exactly 1 to 9 timing (center 8 divisions).
REV. C, SEPT. 1974
5-13

Tektronix 485 Specifications

General

Brand	Tektronix
Model	485
Category	Test Equipment
Language	English