Operating Instructions— Type 1A1
Fig. 2 -1 . Partial diagrams of the plug-in connectors to show why it is necessary to modify the Type 21 and 22 Time-Base units before
inserting the Type 1A1 in the Type 555 upper-beam vertical plug-in compartment.
5. Place the MODE switch to CH 2 and position the trace
1 cm below the graticule centerline with the Channel 2
POSITION control.
6. Place the MODE switch to ALT. Both Channel 1 and 2
traces should be displayed.
7. Set the oscilloscope Time/Cm switch to 50 ms. Note
that for each sweep cycle one channel is displayed and the
other is shut off. Electronic switching from one channel to
the other occurs during the retrace interval.
8. Set the MODE switch to CHOP. Notice that both traces
seem to start simultaneously and continue across the CRT.
9. Set the oscilloscope Time/Cm switch to 5
/is
and adjust
the oscilloscope trigger controls to obtain a stable display.
Notice that each trace is composed of many short-duration
bits or segments with visible switching transients existing
between channels (see Fig. 2-2A).
10. To see the chopped-mode switching action clearly,
increase the sweep rate to 0.2 yis/cm. Notice that Channel
1 is on for about 0.5 /xs while Channel 2 is off for 0.5 /is for
the first half cycle. Then, for the last holf cycle, Channel 2
is on for 0.5 /xs while Channel 1 is off (see Fig. 2-2B). Chop
ping rate per channel, determined by the free-running multi
vibrator switching rate, is about 1 MHz.
11. Blank out the switching transients between channels
by setting the CRT cathode Selector switch (located on the
rear panel of most Tektronix oscilloscopes) to the Dual-Trace
Chopped Blanking position (see Fig. 2-2C).
12. Set the oscilloscope Time/Cm switch to 0.5 ms. Using
coaxial cables, a T connector connected to Channel 1 and
2-2
