HP 5245L Service Manual

Section
II
Paragraphs
2-83
to
2-90
occurs
on counts
6 and 0).
Gate
C
conducts
when
an
input
pulse
is
present
and
transistors
B and C are
both
turned
off
(count
4).
2-83.
OUTPUT.
The common
emitter
amplifier
in-
verts
the output
and
provides
the
voltage
gain
nec-
essary
to drive
the
5 MHz
counter
assembly.
2-84.
50 MHZ
READOUT
ASSEMBLY
A18.
2-85.
GENERAL. The
50
MHz
readout
assembly
(A18)
receives
the
binary-coded
decimal
output from
the
50MHzdecimal
counter
A17; it
provides
both
front-
panel
digital
display and
amplified
binary-coded-
decimal
signals. Circuit
details
are
shown
i.n
the
schematic
diagram, Figure
7-14.
2-86.
AMPLIFIERS.
Transistors
el
through
eB
are
arranged in
four
pairs
(amplifiers
A, B, D, and C).
Each
amplifier
pair
controls
a
pair
of neon
lamps
in
the display
matrix
(for
detailed
discussion
of
digital
display
see
Paragraphs
2-33
through 2-35.
2-87.
AMPLIFIER
OPERATION.
As an
exampte of
amplifier
operation,
suppose
that
the
A
input
became
relatively
negative,
equivalent to
binary
"0",
conduc-
tion
through
Q1
would decrease,
resulting
in
a
rela-
tively negative
voltage at
the
Q1
emitter and a rela-
tively
positive
voltage
at
the
Q1
collector,
thus
per-
mitting
the
A neon lamp
to light;
the output
oflel,
coupled
to
Q2
by
way of
emitter
resistor
R22 and
voltage
divider
R20-R21, results
in
conduction
of
e2,
Model
5245L
the
Q2
collector
voltage
therefore
becomes
relatively
negative,
representing
binary
"0",
and is
supplied
as
the A
output.
Operation is
reversed
upon
receipt
of
a relatively
positive
input
(binary
"1")
and
results
in
Iighting
of
the A neon lamp
and
supplying a relatively
positive
A output,
representing
binary
"1".
The
B
amplifier
(Q3-Q4),
the
D amplifier
(Q5-Q6),
and
the
C amplifier
(Q7-QB)
operate
in
a
similar manner.
2-88.
INPUT
AMPLIFIER
ASSEMBLY
A19.A2O
2-89.
Diodes
CR2,
CR6, CR4,
and CR? together with
current
source
resistors
R25
and R26
provides
two
Iow
voltage
sources that
function together
with
limiting
diodes
CRl
and CR3 to
provide protection
while main-
taining
1
megohm input
resistance
up to
2.8
volts
peak-to-peak (same
voltage
as
the 4
on diodes).
Since
the input resistance
of the
limiting
diodes
in
parallel
with
the temperature
matched
field
effect transistor
(FET)
pair
is
much
greater
than
1 megohm, the input
resistance
is
determined
by the resistors
in the
attenuator
A1.
2-90.
The LEVEL
control
supplies
a
voltage
to the
second
input
without
a
gain
change.
Transistors
Q2A
and
Q3
are a
standard feedback
pair
used in differ-
ential
operation
with feedback
pair
Q2B
and
Q4.
The
feedbackprovides
small
loading
onthe
source follow-
ers, wide
bandwidth,
and
stable
gain.
The second
differential
pair
provides
gain
with temperature
sta-
bility
and
is
a current
source to drive
the twisted
pair
02349-1
o5245-B-5
A. SOMHz READOUT
AIPLI FIIR
A
ATPLIFIER
8.
ATPLI FIER
0.
AIPLI FIER
c.
I
TO
SllHz
c0tJ
ilItR
B. 5OMHz DECIMAL
COUNTER
2-L8
Figure
2-L6.
50 MHz Readout
and 50
MHz
Counter Block
Diagram

HP 5245L Specifications

General

Brand	HP
Model	5245L
Category	Cash Counter
Language	English