Tektronix 502 series, Instruction Manual

Page: 57 / 114

switch in the B DC position and the SENSITIVITY
switch in the 2 VOLTS PER CM position. Set the
Type 105 output amplitude for approximately 3
centimeters of vertical deflection. Adjust C407G
and C407J for an undistorted square-wave.
27. C470 and C489. Place the SENSITIVITY
switch in the .2 VOLTS PER CM position and the
TIME/CM switch in the 50
fiSEC position. Apply
10-kc square-waves from the Type 105 to input
A of the vertical amplifier through the Type
B52-R Terminating Resistor and place the Input
Selector switch in the A DC position. Adjust
C470 and C489 for the best possible square-
wave.
28. C480. Apply 10-kc square-waves from the
Type 105 to input B of the vertical amplifier
through the B52-R Terminating Resistor and place
the Input Selector switch in the B DC position.
Adjust C480 for the best possible square-wave.
Adjustments 27 and 28 interact and the final set­
tings for C470, C480, and C489 should be made
so that the displayed waveform appears the
same when the input square-waves are applied
to either the A or B input connector.
NOTE
For the FEEDBACK BAL adjustment it
w ill be advantageous if you shield
the vertical amplifiers by placing a
metal plate at the side o f the am pli­
fier. The amplifiers are norm ally
shielded by the side panels.
29. FEEDBACK BAL. Apply 200-cycle square-
waves from the Type 105 to the A and B input
connectors through Type B52-T10 T-pads and
Type CS47 Capacitance Standardizers. (The ca­
pacitance standardizers must be connected to
the oscilloscope input connectors.) Place the
SENSITIVITY switch in the 200 ^ VOLTS PER CM
position and the TIME/CM switch in the 1 MILLI-
SEC position. Ignore the noise on the displayed
square-waves and adjust the FEEDBACK BAL
control for the least distorted square-wave for
both the A, DC and B DC positions of the Input
Selector switch.
30. GAIN ADJ FOR HORIZ MODE. Place the
HORIZ DEF PLATE SELECTOR switch in the
UPPER BEAM AMP position and place the UPPER
BEAM SENSITIVITY switch in the 1 VOLTS PER
CM position. Place the Input Selector switch in
the A DC position and connect 10 volts of Cali­
brator signal to the A input connector of the
upper beam amplifier. Adjust the GAIN ADJ
FOR HORIZ MODE control for 10 centimeters of
horizontal deflection.
Fig. 6 -1 0 . Adjustment of the FEEDBACK BAL control.
The waveform shown is typical of the waveforms ob­
tained when the FEEDBACK BAL control is adjusted
properly. The vertical amplifier is shielded by a small
metal plate to reduce the noise level. Note that it is
not usually possible to completely eliminate distortion
of the square wave. The adjustment is made for mini­
mum distortion.
TRIGGERING CIRCUIT
31. TRIG LEVEL CENT. Place the HORIZ DEF
PLATE SELECTOR switch in the TIME BASE AMP
position, the UPPER-BEAM SENSITIVITY switch in
the 1 VOLTS PER CM position, and the TRIGGER­
ING LEVEL control at midrange. Connect 100
millivolts of Calibrator signal to input A of the
upper beam vertical amplifier and place the
TRIGGER SELECTOR switch in the UPPER AC
position. Ground the junction of R15 and C13
(See Fig. 6-11.) by placing a jumper between that
point and the chassis. Adjust the TRIG. LEVEL
m
CENT control so that the sweep will trigger cor­
rectly with the TRIGGER SELECTOR Slope switch
in either the + or — positions.
32. STABILITY ADJUST. Disconnect the Calibra­
tor signal, remove the jumper from the junction
of R15 and C13 to ground, and place the TRIG­
GERING LEVEL control in the AUTOMATIC posi­
tion. Connect a meter from the wiper arm of the
STABILITY ADJUST potentiometer to ground. Ro­
tate the STABILITY ADJUST control clockwise
from the fully counterclockwise position. Note
RECALIBRATION PROCEDURE — TYPE 502
6-7