HP 5245L Service Manual

Model
5245L
I
l
Figure 2-19.
Sampling
Control
Block
Diagram
of
both the
gate
flip-flop
and
amplifier
Q10
are
com-
bined,
then amplified
by A11
to drive the front-panel
GATE lamp;
the GATE lamp
is
therefore
on during
the
gating
signal
plus
30
milliseconds;
this
ensures
a
visible flash from
the lamp
even for very
short
gates.
2-98.
CIRCIIIT
DETAILS.
Refer
to the schematic
diagram,
Figure 7
-19,
for
circuit
details. AII
cir-
cuits
are conventional;
flip-flop
operation
is described
in Paragraphs 2-15
and
2-16,
and one-shot
multi-
vibrator
operation
is
described in Paragraphs
2-19
thru 2-22. The
steering amplifiers
(Q2
and
Q3)
are
common-base
amplifiers;
one
amplifier
(whose
col-
lector
is
connected to
the collector
of the conducting
flip-flop
transistor) cannot
operate
because
of low
collector
voltage;
the other amplifier
(whose
collec-
tor is
connected
to the collector
of
the
cut-offflip-flop
transistor) amplifies
the
gate
triggering
pulse
and
supplies it
to
the
receptive
flip-flop
transistor.
2-99. SAMPLING
CONTROL ASSEMBLY
A23.
2-100.
GENERAL. During
normal
operation, the
sampling control
assembly receives
the
positive
trans-
fer
pulse
and
the
sampling trigger
pulse
from A22;
its
outputs are a)
the amplified
and inverted
transfer
pulse,
b)
reset
pulses
for
the decimal
counters
and
decade dividers,
and c)
the
holdoff
signal
which
pre-
vents
retriggering
of
the
gate
flip-flop
tn
A22.
Refer
to the block diagram, Figure 2-19,
during the
fol-
Iowing
explanation.
g.?31?;'
2-101.
TRANSFER PULSE. The
positive
transfer
pulse
is amplified
without
inversion
by
Ql,
then
amp-
Iified and
inverted
by
Q2.
During manual reset
(RE-
SET
pushbutton pressed
or
FUNCTION or TIME-BASE
switches
operated)-15volts
is amplified and
inverted
by
Ql,
then amplified
and
inverted
by
Q2
to
produce
a manually
generated
equivalent
of
the transfer
pulse.
Action
of other circuits
resets
all decimal counters
to
zerobeforethe
reset contacts
open; then the
voltage
on the transfer
pulse
line
transfers
the zero
count to
the
front-panel
numerical display.
2-t02.
RESET.
The negativetransitionof
the samp-
Iing
trigger
pulse
from A22
normally
triggers
the
sample-rate
one-shot
multivibrator
and
starts opera-
tion of all
sample-rate
control
circuits. Multivibrator
feedback
is
through
quick-recovery
amplifier
Q?,
capacitor
C4,
and
emitter follower
Q5.
The
sample-
rate
outputpulse
duration
is controlled
bythe SAMPLE
RATE
potentiometer
andis
variable between 55 milli-
seconds and
5
seconds. When
the SAMPLE-RATE
control is
operated
to the HOLD
position
(completely
clockwise),
the multivibrator
provides
a eontinuous
output.
An amplified
output is
taken from
Q?,
differ-
entiated
(leading
edge
is
selected), amplified
by
QB,
and
supplied
as the DCA reset
pulse
and
the
DDA reset
pulse.
If
manual
resetoccurs
during
the sample-rate
multivibrator
cycle,
the multivibrator is
quickly
re-
turned
toits
quiescent
state
as a result
of
the
-15volt
input
through
CR3.
Section
U
Paragraphs
2-98
to
2.102
ig-ioi3gr-,r
A22
(6)
OUTPUT OF
TRANSFER
MVB
I
RESEr
I
-.1-
Lo-lli
.--''
Lo_ui
A3StE(R-9
t/2)
J|
(22)
INHIBIT
SIG
FROM
DR
A2?el
SAMPLING
TRIGGER
L
PART
OF A3
PART
OF
A3
Aro- A
t7
DCA
RESET
A
3t
-A34
DDA
RESET
A22
(7'
HOLDOFF
PULSE
PULSE
-t5v
CLOSED
MAX
CW
TO
53
IOPENS
LINE
MAX
INHIB
INPUT
2-2L

HP 5245L Specifications

General

Brand	HP
Model	5245L
Category	Cash Counter
Language	English