Tektronix 5T1A Instrument Reference Book page 97

Type STIA Page 2-15
, Turn the TIME POSITION control fully clockwise. It
can later be set to bring the desired signals in |
view on the crt. Set the TIME EXPANDER switch to X1.
Set the RECOVERY TIME control to MIN.
Set the THRESHOLD control to hold off the sweep
(cw +, cew -). Turn the control toward zero for
proper triggering.
If triggering difficulties occur, establish whether
the trouble is due to: (a) too low or too high.
trigger amplitude, (b) too high a trigger-signal
repetition rate, (c) too low a rate of rise (or fall)
of trigger-signal voltage, or (d) interference due
to recovery time. The cause can usually be found
by operating the SWEEP TIME/CM switch, THRESHOLD,
and RECOVERY TIME controls. Inability to hold off
the sweep with the THRESHOLD control indicates too
large a trigger 'signal. Use an input attenuator to
reduce amplitude. If advancing the THRESHOLD control
causes the sweep to free-run before obtaining a
stable display, either amplitude or rate-of-change
is too low. If the problem is high repetition rate,
and moving the RECOVERY TIME control does not stabi-
lize a display, an external trigger-countdown unit
such as Tektronix Type 280 may be needed. If the
signal has a low rate of rise (for example, sinewaves
"'pelow.dbout 50 kc), a faster-rising trigger signal
is needed. (De triggering is available internally
only. See sampling unit instruction manual.) TF