HP 5245L Service Manual

Section II
Paragraphs 2-94
to
2-9?
that the
selected
frequency
(always
100
kHz) from
the
time base control
assembly A35
becomes the driving
signal
for the
second
group
of decade
dividers.
2-94.
CIRCUIT
DETAILS.
Refer
to
the schematic
diagram, Figure 7-18,
for
circuit
details.
The
basic
Ai'{D
gate
description
given
in Paragraph
2-6 applies
to
the
gate
circuits,
but note
that
gates
1
through
6
consist
of two diodes.
The
gates
are
turned on
(sig-
nal
passes)
when
-15
volts is
applied
to the control
input
to
forward-bias
the diodes;
the
gates
areturned
off
(signal
btocked) when
the
-15
volti is removed
so
that
the
fixed
bias
supply
(from
+13
volts) reverse-
biases the diodes. The
main
gate,
Q10-Q11,
is
open
when the
gating
signal
amplifier A12
is off,
allowing
the
pulses
from
amplifier
Q9
to
switch
the
current
flowing
through
Q10
to
Ql1
and
to the output
pulse
amplifier
Q13.
The main
gate
is closed when
Q12
is
conducting which turns
off transistors
Q10
and
Ql1.
Thus the
pulses
from
Q9
are
not allowed
to
drive the
output
pulse
amplifier
Q13.
2-95.
GATE CONTROL
ASSEMBLY
A22.
2-96.
GENERAL.
The
main function
of the
gate
con-
trol assembly
is
to
generate
the
gating
signal
(which
controls
the main
gate
in
A21) and
the
sampling trig-
ger
(which
starts the
sample-rate
multivibrator
in
A23).
Refer
tothe
block diagram,
Figure
2-18,
during
the following
discussion.
Model 5245L
2-97.
SIGNAL
FLOW.
The
gate
flip-flop
(ea-es)
is
normally
held
in its
off
state
(in
this
state,
it
holds
the main
gate
closed,
preventing
counting)
by
the
hold-
off
signal
from
A23
which
is
applied
through
e6.
The
first
gate
triggering
pulse
which occurs
after
the
end
of
the
holdoff
pulse
is
amplified
by
Q1
and
steering
amplifier
Q2
and
operates
the
gate
flip-flop
to its
on
state. The next
gate
triggering
pulse
turns
the
gate
flip-flop
off through
Ql
and
Q3.
(In
MANUAL
opera-
tion
-15volts
is
applied as
a
start or
stop signal thru
CR1
or CR2
to
turn the
gate
flip-flop
on
or off.
)
The
gate
flip-flop
output
(positive
pulse)is
amplified
with-
out inversion
by split-Ioad amplifier
Q?
and
passed
on
to A21
as
the
gating pulse.
The
trailing
edge of the
inverted
output from
QT
triggers
the
transfer
one-shot
multivibrator
(Q8-Q9)which
produces
a 30-millisecond
output
pulse;
the negative
pulse
output
is
supplied
di-
rectly
from
the multivibrator as
the
print
command
pulse (negative
transition
tells digital
recorder
to
accept
BCD information
from
counter);
the
positive
pulse
output from
the multivibrator
is
a)immediately
fed
back to the
gate
flip-flop
as a hold-off
signal thru
Q6
to
prevent
retriggering
of
the
gate
flip-flop
until
the regularholdoff
signal fromA23 is
generated
about
a microsecond
later,
b) delivered
to
A23
for
amplifi-
cation
as
the transfer
pulse,
and
c) amplified
and
in-
verted
by
Q10.
The
Q10
output is
delivered
to
A23
as
the
sampling
trigger
pulse.
(In
MANUAL
operation
the
sampling
trigger
output is
shorted
to
ground
by
the
FUNCTION
switch). The
negative
pulse
outputs
SYNC TO HOLD-
OFF MVB
A23(
r5)
TO
GATE
LIGHT
TRANSFER
PULSE
TO a23
(2)
SAM PLING
TRIGGER
TO
A23
(4)
GATE
TRIGGERING
FROM A2I
(GATES
t2,t3)
r'rc!3
sToP slc ,nl
FRoM
Alstc
(F-t)
=l
AND
J6
(22)
I
NEG
PRINT
COMMAND
TO
Jil
(48)
GATING
SIG
TO
A2I
(MAIN
GATE)
START SIG ,=l
FROM A35tC(F-2):+
AND
J6
(2I)
HOLDOFF
FROM
A23
(tO)
STEERING
GATES
02349-1
osznc-d-g
2-20
Figure
2-L8. Gate Control
Block
Diagram

HP 5245L Specifications

General

Brand	HP
Model	5245L
Category	Cash Counter
Language	English