Tektronix 3A74 Instruction Manual page 61

except that the signal is applied to channel 3.) Set channel
4 MODE switch to OFF and channel 3 MODE switch to
NORM. Perform the channel 3 adjustments in the same man-
ner as described for the channel 4 adjustments. Then, repeat
the procedure for channels 2 and 1.
After completing the channel 1 adjustments, decrease the
Type 105 output level to minimum and disconnect the 47-pf
Input Time-Constant Standardizer from the channel 1 Input
connector.
Alternate Method
To use a 10X attenuator probe as an emergency standard-
izer, proceed as follows:
a. Connect the cable end of the 10X attenuator probe to
a channel that has not been repaired. (We are assum-
ing here that the non-repaired channel is properly ad-
justed as set at the factory and this channel will be
used as the reference.}
b. Set the VOLTS/DIV. switch of the reference channel to
.02, the AC-GND-DC switch to DC, and the MODE
switch to NORM.
c. Connect a 5XT attenuator (item 10) to the output con-
nector of the square-wave generator. Set the generator
for an output frequency of 1 kc.
d. Connect the probe tip to the other end of the 5XT
attenuator and connect the probe ground lead to the
generator ground, Adjust the generator amplitude
control to produce a deflection of four major divisions
on the oscilloscope crt.
e. Adjust the variable capacitor in the probe for best
square-wave response.
The probe is now standardized to match the input time
constant of the reference channel. Do not adjust the probe
further during the procedure. Disconnect the cable end of
the probe from the reference channel and connect it to the
channel that needs to be standardized.
With the signal applied to the probe tip, the adjustments
listed in step 3 and Table 5-2 can be performed in the same
manner as if you are using a 47-pf Input Time-Constant
Standardizer.
14. Adjust Composite Int. Trig. DC Level
a. Set the time-base triggering Level control to free run
the time base.
b. Position the channel 1 trace to the graticule horizontal
centerline.
c. Connect a voltmeter between pin 11 of the left-hand
oscilloscope vertical-amplifier interconnecting socket
and ground. (If pin 11 is difficult to reach, connect the
voltmeter to pin 12 of the right-hand interconnecting
socket in the oscilloscope which has an X-axis plug-in
compartment.)
d. Adjust the COMPOSITE INT. TRIG. DC LEVEL R530
control (see Fig. 6-2) for a zero voltage reading on the
voltmeter. Overlook the normal {few tenths of a volt)
drift in voltage reading.
Calibration — Type 3A74
15. Adjust Chan. 1 Int. Trig. DC Level
a. Pull the TRIGGER switch outward to the CH 1 ONLY
position.
b. With the voltmeter connected as directed in step 14
and with the trace positioned to coincide with the
graticule horizontal centerline, adjust CHAN. 1 INT.
TRIG. DC LEVEL R521 control (see Fig. 6-2) for a zero
reading on the voltmeter. Overlook the normal (few
tenths of a volt) drift in the voltage reading.
c. Disconnect the voltmeter.
16. Check Chan, 1 Trigger Output
a. Set channel 1 VOLTS/DIV. switch to .02,
b. Connect the 5XT attenuator to the output connector of
the square-wave generator.
c. Connect a 50-ohm coaxial cable to the 5XT attenuator
and connect the other end of the cable to a 50-ohm
termination.
d. Connect the plug-end of the termination to the channel
1 Input connector. (This setup is similar to Fig. 6-5
except the 47-pf Input Time Constant Standardizer is
not used.)
e. Set the generator frequency for an output of approxi-
mately 100 kc.
f. Increase the output amplitude from the generator to ob-
tain a vertical deflection of exactly 4 major divisions.
r
£
12 Volts ' a |
or more tp
(a) Sweep Rate: 5 uSec/Div.
T 1 1 | 1
T T T T T t
Sweep Rate: 0.4 uSec/Div.
80% tt 7
'o er +
HHH H+ 4+ vba HHH +H+
10% -- +t
Th) +
—s| 07
psec
or faster
risetime
Fig. 6-8. (a) Typical channel 1 only trigger waveform as displayed
on the test oscilloscope crt. Vertical deflection factor: 5 volts/div.
(b} Measuring the risetime of the waveform. Vertical deflection
factor: uncalibrated (see step 16i).
6-9