Service
When
Schmitt
trigger
08
/
09
is
switched by an
external
trigger signal, positive
and
negative spikes
are generated by L 1,
the
negative spike switching
010
on.
Transistor
011
cuts
off
and
the
rate
Schmitt
trigger
(034
/
036)
toggles
once,
the
disable voltage
at
CR14
cathode
being removed
for
the
duration
of
the
spike.
Also
in
EXT
TRIG
mode,
the
rate selector switches S2D
to
S2f are disabled
by
removing +5 V
at
S1
b/pin 17 (signal
23).
Gate Mode
With GATE
mode
selected:
current
sources
022
and
023
are disabled
current
source
025
is
switched
on
rate
Schmitt
trigger
034
/
036
is
disabled via
011
and CR
14
current
source
024
is
switched
on.
When
the
gate signal
is
present
at
the
EXT
TRIG
connector,
the
TP1 signal goes low.
010
collector
follows with a low and switches
010
on.
The
disable signal
at
CR14
cathode
for
the
rate
Schmitt
trigger
is
removed
and
pulses are
generated
for
the
duration
of
the
gate
signal (becauses
09
collector
remains
low during this
time).
Manual Trigger
When
MAN
is
selected
at
the
MAN /NEG /POS switch, CR11
is
forward
biased
with
the
effect
that
increased
current
is
del ivered
from
05
to
current
node
CR7 /C R8.
The
TP1 signal
is
therefore
held
at
a high level,
turning
08
and
011
on
and disabling
the
rate
Schmitt
trigger
034
/
036
via
the
voltage
at
C R
14
cathode
.
Pressing
the
MAN
pushbutton
then
generates
a single pulse
at
U7/pin 7
(the
duration
of
which
depends
on
how
long
the
pushbutton
is
pressed) which
turns
083
on
and
reverse biases CR 11. With
less
current
now being delivered
to
the
CR5
/CR6 node,
the
voltage
at
TP1
drops,
turning
08
off
and
09
on.
Depending
on
whether
GATE
mode
or EXT
TRIG
mode
is
selected,
determines
whether
a
negative-going spike
or
a negative-going pulse (of
the
same
duration
as
the
MAN
pushbutton
is
pressed)
is
generated. If GATE
is
selected, a negative pulse
is
generated which
functions
as a gate signal
for
the
rate
Schmitt
trigger i.e.
the
disable voltage
at
CR
14
cathode
is
removed
for
the
duration
of
this pulse.
If
EXT
TRIG
is
selected, a negative spike causes
the
disable signal
to
be removed
momentarily
allowing
the
rate
Schmitt
trigger
to
switch
once.
Burst
Mode
(Schematic A
1-2)
With
BURST
mode
selected,
only
current
source
024
is
switched
on.
The
rate
Schmitt
trigger
is
disabled
by a high level derived
from
A60304,
which
is
turned
on
by flip·
flop
A6U319
(cleared
when
burst
counters
have
count
down).
The
burst
can be
started
either
by
pressing
the
MAN
pushbutton
(with
MAN selected
at
the
MAN
/NEG /
POS switch)
or
by
applying
the
appropriate
signal
to
the
EXT
TRIG
connector.
In
either
case, a
negative·going edge
is
generated
at
TP1 which causes
the
A208
collector
to
go high. This resets
A6U319
via
A60305
causing
A60304
to
be switched
off.
The
disable signal
is
thus
removed
from
the
rate
Schmitt
trigger
which
now
switches
continuously
until
the
'end
of
burst'
has been
detected.
Flip-flop
A6U319
is
then
cleared again
and
the
rate
Schmitt
trigger disabled.
8-24
Model 214B
Scans by ArtekMedia => 2009
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