Tektronix 549 Instruction Manual page 120

d. Adjust Erase Positive R1033, for minimum amplitude.
If mottled areas appear on the target, increase the amplitude
until these disappear. If this adjustment appears to have no
effect, set the adjustment for minimum amplitude.
targets w ill erase properly at minimum amplitude.
e. Check erase pulse for a time duration of 70 to 130 ms.
Fig. 6-50.
f. Slow ly reduce the Erase Negative amplitude by adjust­
ing Erase Negative R1033, until the target fails to erase
properly. Th is is the critical value for good erasure. Increase
the amplitude 20 volts from this critical erase value. Do not
permit the bottom of the negative pulse to square or limit.
In some instruments this critical value may not show.
this occurs, adjust R1033 for minimum negative amplitude.
56. Check Viewing Time and After Sweep Auto
Erase
a. Equipment setup is as given for step 55.
b. Change the A U TO ERASE switch to PERIODIC position.
c. Set the test oscilloscope Time/Cm switch to 1 sec.
d. Measure the viewing time with the V IE W IN G TIM E con­
trol fully counterclockwise.
should equal or be less than 0.5 seconds.
e. Measure the viewing time with the V IE W IN G TIM E con­
trol fully clockwise. The time between erase pulses should
equal 5 seconds or more.
f. Change the A TIM E/C M switch to 0.1 SEC position and
set the A U TO ERASE switch to AFTER SWEEP.
g. Check for an automatic erase and reset after each
sweep with a variable time between consecutive erase and
single sweep cycles determined by the V IE W IN G TIM E con­
trol position.) Time between erasures should be the same as
the previous check on viewing time.
h. Change the A U TO ERASE switch to the O FF position
and press the ERASE AND RESET button.
i. Check— The screen should erase, followed by a single
sweep which stores.
57. Adjust Non Store Level
a. Equipment setup is as given for step 56.
b. Push both UPPER and LO W ER SCREEN STO RA G E OFF
buttons for conventional operation.
c. Set the N O RM -SIN G LE SW EEP switch to NORM.
d. Turn the Non Store Level R1169 fully counterclockwise.
e. Adjust the IN T E N S IT Y control for a sweep of nominal
intensity.
Many
The time between erase pulses
If
F ig . 6 - 5 0 . E ra s e w a v e fo rm .
f. W rite the complete storage area by vertically position­
ing the free running sweep over the screen storage area.
g. Rotate the Non Store Level clockwise until the screen
is no longer stored.
h. Switch the screen storage to STO RE and again write
the screen storage area.
i. Switch the screen storage to OFF position.
screen remains stored or is slow to erase, rotate the Non
Store Level adjustment further clockwise.
j. Repeat this procedure until the screen erases promptly
when the screen storage is switched from STO RE to OFF.
58. Adjust Enhance Width and Enhance
Level
a. Equipment setup is as given for step 57.
b. Change the EN HA N C E M ODE switch to the FULL posi­
tion and set the EN H A N C E LEVEL control midrange. Set the
A U TO ERASE switch to AFTER SW EEP and the V IE W IN G
O
TIM E control to M IN position.
c. Connect the test oscilloscope 1 0 X probe to TP Upper,
on the circuit board assembly.
d. Connect a coaxial cable from the Type 549 + G ATE
A connector to the test oscilloscope Trig Input connector.
Trigger the test oscilloscope with the -f-G A TE A signal.
e. Adjust Enhance W idth
width of 1 ms, Fig. 6-51B (enhance pulse appears after the
erase cycle).
Calibration— Type 549
~ 3 0 ms
R1132 for an enhance pulse
If the
O