Tektronix 485, Instruction Manual

Page: 67 / 197

Calibration—4 8 5 /R 4 8 5 Service
c. Use the A LEVEL control to trigger on the larger of
the positive steps. This should give a 3.3 div display
(167 mV) on CH 2. Use CH 2 POSITION control to center
c. Reset lamp should light.
the CH 2 step vertically.
d. Apply signal, should have one sweep, READY light
should go off.
d. Hold the A EXT TRIG pushbutton and use the A
LEVEL to center the large step vertically. Use POSITION
(HORIZ) to set the 50% amplitude point exactly 0.1 div to
e. Remove signal and reset. RESET lamp should light.
the right of center screen (this 0.1 ns offset compensates
for the delay through the one 50 £2 BNC termination).
79. CHECK A E X T T R IG RESPONSE
e. Check for 0.5 ns or less delay match of EXT TRIG to
CH 2 50 £2 (±0.5 div).
a. Connect TD Pulser through a 50 £2 termination to the
A EXT TRIG input.
f. Add a 50 £2 BNC termination at CH 2 input; CH 2
input to 1 M£2.
b. Depress the A EXT TRIG switch and check risetime
to less than 1.6 ns.
g. Repeat step d, but use POSITION (HORIZ) to set
80. ADJUST X -Y BALANCE (Located Rear of
Sweep Board)
50% amplitude point exactly to center screen.
a. Set VERT MODE to ALT; VOLTS/DIV to 20 mV.
h. Check for 0.5 ns or less delay match of EXT TRIG to
CH 2 1 M£2 (±0.5 div).
b. Center both traces.
77. CHECK E X T E R N A L TR IG G E R LEVEL
RANGE A and B
c. Set VERT MODE to X-Y.
a. Connect 1 V from the Amplitude Calibrator to A
EXT TRIG; A TRIGGER SOURCE to EXT; SWEEP MODE
to NORM.
d. Adjust X-Y center (R1355 located on Sweep board)
to center spot.
b. Rotate LEVEL and check that sweep stops running
at both ends of the LEVEL range.
81. ADJUST X -Y G A IN (Located Rear of V erti­
cal Board)
a. Connect 120 mV from 50 £2 Amplitude Calibrator to
CH 2 50 £2 input impedance.
c. Amplitude Calibrator to 10 V; A TRIGGER
SOURCE to EXT -r 10.
b. Adjust X GAIN (R575) for 6 div, must match CH 2
gain ±1%.
d. Rotate LEVEL and check that sweep stops running
at both ends of the LEVEL range.
c. 5 mV/div to 5 V/div gain accuracy ±2%.
e. SWEEP MODE to AUTO; HORIZ DISPLAY to B.
82. ADJUST X -Y PHASING (Located Rear of
Sweep Board)
f. Repeat for B.
a. Connect CH 1 and CH 2 to Type 191 generator
through dual input cable.
78. CHECK SING LE SWEEP
a. Trigger A Sweep on 1 div of 50 kHz.
b. Apply 10 div of 50 kHz; CH 1 to 50 mV, CH 2 to
20 mV.
b. Remove signal and switch to SINGLE SWEEP.
c. Switch to 4 MHz.
REV. C. AUG. 1975
5-23