Philips PM 3266 - 3.2.4. Delayed time-base triggering

115
In this
way,
the
time-base
generator
runs
automatically
without
the
intervention
of
a trigger
pulse.
Transistor
V937
IS
conductive
when
the
time-base
generator
is
not
triggered.
The
base
of V939
is
then
low,
as
a result
of
which
the
transistor
conducts
and
the NOT
TRIC'D
lamp
(V2) lights.
3.2.3.2.
SINGLE
SHO
T
mode
In
the
trigger
position
SINGLE,
the
time-base
hold-off
capacitors
are
short-circuited
by diode
V953
and
switch
contacts
S8 (AUTO)
and
S8 (TRIGG).
The
flip-flop
D902
must
then be
reset
manually
by the RESET
button
S8 (SINGLE),
which
applies
+5.2
V via
R975,
V946to
input
10. After
input
10 has been
brought
to
a
high
level
and the
RESET
button released,
triggering
can
occur,
but on one
event
only
as the flip-flop
is not
reset
automatically.
In
the SINGLE
mode, V937
is
permanently
turned
off via R965
by
S8 (AUTO)
and
S8 (SINGLE).
Since
diodes V941
and V942
are now
conductive,
the pulse
on output 14
of D902
will be
transferred
to the
base
of V939.
Consequently,
the NOT
TRIC'D
lamp will
light during
the period when
output 14
of D902
is
low,
i.e. from
the
moment the
RESET
button is
pressed until
the end of the
time-base sweep
initiated
by the incoming
trigger
pulse of
the
event under
observation.
3.2.4.
Delayed
time-base triggering
The trigger
source
switches for triggering
the delayed
time-base generator, can
select any of the following
input
sources.
—
an internal signal
from the vertical
A channel
—
an internal
signal from
the vertical B channel
—
an internal
signal
derived
from the main
time-base
to
start the delayed time-base
immediately
after
the
selected
delay time
—
an external source
Source selection
is done
by means of
a
trigger selector switch
S21
.
3
TRIGG
I
FvF..’Si05>F
’HIGL4H PJLbt
*0
jELAYF?
'IMF nAr.E
BASE
SWEEP
GATING
^00-C
Fig.
3.9. Delayed timeLiase
trigger
circuit.