HP 547A Service manual
CERTIFICATION
Hewlett-Packard Company certifies that this instrument met its published specifications
at the time
of
shipment from the factory. Hewlett-Packard Company further certifies that
its calibration measurements are traceable to the United States National Bureau
of
Standards,
to
the extent allowed by the Bureau's calibration facility, and to the calibration
facilities
of
other International Standards Organization members.
WARRANTY AND ASSISTANCE
This Hewlett-Packard product
is
warranted against defects in materials and workmanship
for a period of one year from the date of shipment. Hewlett-Packard will, at its option,
repair
or
replace products which prove to
be
defective during the warranty period pro-
vided they are returned to Hewlett-Packard, and provided the preventive maintenance
procedures in this manual are followed. Repairs necessitated by misuse
of
the product
are not covered by this warranty.
NO
OTHER WARRANTIES ARE
EXPRESSED
OR
IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
MERCHANTABILITY AND FITNESS
FOR
A PARTICULAR
PURPOSE.
HEWLETT-
PACKARD
IS
NOT LIABLE
FOR
CONSEQUENTIAL DAMAGES.
Service contracts
or
customer assistance agreements are available
for
Hewlett-Packard
products.
For any assistance, contact your nearest Hewlett-Packard Sales and Service Office.
Addresses are provided at the back of this manual.
CURRENT
TRACER
547A
OPERATING
AND
SERVICE
MANUAL
SERIAL
NUMBER:
AOOOS1
and above
This manual refers directly to
Model
547A
Current Tracers with Serial
numbers
A00051.
NEWER
INSTRUMENTS
The changes in Current Tracers with Serial numbers higher than
A00051
are described in "Change Sheets" included with the manual.
Copyright
HEWLETT-PACKARD
COMPANY
1976
5301
STEVENS
CREEK
BLVD.,
SANTA
CLARA,
CALIF.
95050
Manual Part No. 00547-90006
Microfiche Part No. 00547-90007
Printed:
JAN
1978
Printed in U.S.A.
FJ/o-
HEWLETT
a:t:.
PACKARD
Modei547A
TABLE
OF
CONTENTS
Tide
Page
Scope of Manual . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Instrument Identification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Unpacking and Inspection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Storage and Shipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Operating Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Current Tracer
Operation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
Theory of
Operation
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Performance Tests . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
Table
1.
2.
3.
LIST
OF
TABLES
Page
Model
547A
Current
Tracer Specifications . .. . . .. . . . . .. . . . .. . . . .. . . .
..
. . . .. . . .. . 2
Replaceable Parts list . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Manufacturers
Code
list
......................................................
12
Page
ii
Figure
1.
2.
3.
4.
5.
6.
7.
8.
9.
LIST
OF
FIGURES
Page
HP
Model
547A
Current
Tracer
..
......
. .
..
..
.
......
....
.
..
..
..
..
..
..
.
..
..
.
....
1
Wire-AND
Node
Fault . . . . . . . . . . . . •. . . •••. •. . . . . . . . . . . . . . . . . . . . . . . •. . . . . . . . . . . 4
Gate-to-Gate Faults . . . . . . •. . . . . . . . . . . . . . . . . . . . •. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
Solder-Bridge in Printed-Circuit . . . . . . . . . . . . . . ••. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Multiple
Gate Inputs . . . . . . •. . . . . . . . . . . . . •. . •. •. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
Exploded View
of
Current Tracer . . . . . . . . . . . . . . . . . . . . •. . . . . . . . . . •. •. •. . . . . .
..
. . 7
Setup
for
1 rnA Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Setup
for
1 A Test
.....•.....•............•...................................
10
Schematic Diagram . . . . . . . . . . . . . . . . . . . . . . •••. . . . . . . . . . . . •. . •. . . . . . . . . •. . . . . . . .
13
Model
547A
Page 1
Figure
1.
HP
Model
547A
Current
Tracer
SCOPE
OF
MANUAL
This manual contains information about the Hewlett-Packard
547A
Current Tracer. Coverage includes a description
of the instrument, its applications, specifications, instructions in
its
use, theory
of
operation, maintenance, perform-
ance tests, adjustments, list
of
replaceable parts and how
to
obtain them, component locators, and schematics.
DESCRIPTION
The
HP
547A
Current Tracer
is
a hand-held probe which enables the precise localization
of
low-impedance faults
in electrical systems. The probe
senses
the magnetic field generated by a pulsing current internal to the circuit
or
by current pulses supplied by
an
external stimulus
such
as
the
HP
546A
or
10526T
Logic Pulsers. Indication
of
the
presence
of
current pulses
is
provided by lighting the indicator lamp near the Current Tracer tip. Adjustment of
probe sensitivity over the 1 mA
to
1A range
is
provided by the
SENSITIVITY
control near the indicator. The probe
is
self-contained and requires <75 mA at 4.5V
to
18V, from any convenient source.
INSTRUMENT
IDENTIFICATION
Hewlett-Packard
uses
a
6-digit
serial number
(AOOOOO)
to
identify the Current Tracer.
If
the serial number of
your instrument differs from
the
serial number(s) on the title page
of
this manual, there are other differences
between the manual and your instrument.
These
differences are covered in a
"MANUAL
CHANGES" sheet
which
is
included with the manual.
Model
547A
SPECIFICATIONS
Table 1 lists
all
specifications for
HP
Model
547A
Current
Tracer.
Table
1.
Model
547A
Current Tracer Specifications
INPUT:
Sensitivity: 1
rnA
to
1A
Frequency Response:
light
indicates Single-step
current
transitions: single pulses
2:50
ns
in
width; pulse trains
to
10
MHz (typically
20
MHz for current pulses
2:10
rnA)
Risetime: Light indicates
current
transitions with risetimes
:>.200
ns at 1
rnA.
POWER
SUPPLY
REQUIREMENTS:
Voltage: 4.5
to
18
Vdc
Input
Current:
95
rnA
Maximum Ripple: ±500
mV
above 5 Vdc
Overvoltage Protection: ±25 Vdc for
one
minute
TEMPERATURE: 0°
to
55°C
WEIGHT: 113.4 g
(4
oz.) net; Shipping Weight:
170
g
(6
oz).
Size
Probe
body 15.24 em
(6
in.); Cable, 110.38 em
(47
in.)
Page
2
200
n5 2 1'5
20
1'5
200
1'5
INPUT PULSE RISETIME
APPLICATIONS
The
Current
Tracer
operates
on
the
principle that whatever
is
driving a
low-impedance
fault
node
must
be
de-
livering
the
majority
of
the
current.
Tracing
the
path of this
current
leads directly
to
the
fault. Prob\ems
that
are
compatible with this
method
are:
a. Shorted inputs of integrated circuits.
b. Solder-bridges
on
printed-circuit
boards.
c. Shorted
conductors
in
cables.
d. Shorts
in
voltage distribution networks,
e.g.,
Vee-to-ground
shorts.
e. Stuck data buses, such
as
three
state,
open-collector,
or
Hewlett-Packard Interface
Bus
(HP-IB).
f.
Stuck wire-AND structure.
UNPACKING
AND
INSPECTION
If
the
shipping carton
is
damaged,
ask that
the
carrier's agent
be
present
when
the
Current
Tracer
is
unpacked.
Inspect
the
instrument for obvious
damage
such
as
dents, scratches, etc.
if
the
instrument
is
damaged or
fails
to
meet
performance tests, notify
the
carrier
and
the
nearest Hewlett-Packard Sales and Service Office immediately.
Retain
the
shipping carton and
the
padding
material for
the
carrier's inspection. The Sales and Service Office
will
arrange for
the
repair
or
replacement
of
the
instrument without waiting for
the
claim against
the
carrier
to
be
settled.
STORAGE
AND
SHIPMENT
To
protect
valuable electronic
equipment
during storage
or
shipment, always use
the
best packaging methods avail-
able. Your Hewlett-Packard Sales
and
Service Office can provide packaging material such
as
that used for original
Modei547A
Page 3
factory packaging. Contract packaging companies in many cities
can
provide dependable custom packaging on
short notice. Environmental conditions during storage and shipment should normally be limited
as
follows:
a.
Maximum altitude: 25,000 ft.
b.
Minimum
temperature: -40°F (-40°C).
c. Maximum temperature: +149°F (+65°C).
OPERATING
CHARACTERISTICS
Three conditions must be met before the Current Tracer
can
properly respond
to
circuit stimulus:
1.
The mark on the probe's tip must be aligned along the length
of
the printed-circuit trace.
2.
The probe be held perpendicular
to
the printed-circuit trace -not
at
an
angle.
3. The printed-circuit trace must be conducting
an
alternating current, either from
an
internal source or,
from
an
external stimulus such
as
a Logic Pulser with a rise-time
of
~200
ns.
NOTE
The
voltage present on the
black
power
supply
lead
(negative side of
supply)
is
also
present on the
tracer's
anodized
aluminum
case. Do not
lay
the
tracer
on
any
grounded
area,
such
as
an
instrument
chassis,
unless
the
chassis
is
at
the
same
potential
as
the
black
lead.
Damage
to the
power
supply
may
result.
CURRENT
TRACER
OPERATION
Use
of
the Current Tracer
is
indicated when conventional troubleshooting reveals a low-impedance fal.lft. The
operator aligns the mark on the probe
tip
along the length of the printed-circuit trace
at
the driver and adjusts
the sensitivity control until the indicator lamp just lights. The probe
is
then moved along the trace
or
placed
directly on the terminal points
of
the nodes (or IC pins), while observing the indicator light. This method
of
following
the path
of
the
current
leads directly
to
the fault responsible
for
the abnormal current flow.
If
the
driving
point
does
not
provide
pulse stimulation,
the
node may be driven externally by using a Logic Pulser at
the
driving
point.
The
following
paragraphs describe troubleshooting techniques
for
some
of
the more common
problems.
Wire-AND
Node
One
of
the most
difficult
problems encountered in troubleshooting integrated circuits
is
a stuck
wire-AND
node.
Typically, one
of
the
open-collector
gates may still
continue
sinking
current
after
it
has
been turned off. The
Current
Tracer provides
an
easy
method
of
identifying the fault gate.
Referring
to
Figure 2 place the
Current
Tracer
on
the gate side
of
the
pull-up
resistor. Align the mark
on
the probe
tip
along
the
length
of
the
printed-circuit
trace and adjust the probe's sensitivity control until the indicator
is
just
fully lighted.
If
the
indicator
will
not
light
-
use
a Logic Pulser
to
excite the line. Place
the
tracer tip
on
the
output
pin
of
each gate;
only
the
faulty gate
will
cause the indicator
to
light.
Gate-to-Gate
Faults.
When a
low-impedance
fault exists between
two
gates, the
Current
Tracer and Logic Pulser combine to quickly
pinpoint
the defect. In Figure 3 gate A's
output
is
shorted
to
ground. Place the pulser midway between the
two
gates
and place
the
Current
Tracer's
tip
on
the
Pulser's pin.
Pulse
the line and adjust the Current Tracer's sensitivity
control until the indicator just lights. First place the Current Tracer
tip
next
to
gate A and then gate B
while
con-
tinuing
to
excite the trace. The tracer will
light
only
on
the gate A side, since gate
A,
(the defect in this example),
is
sinking the majority
of
the
current.
Model
547A
AT
LEAST ONE INPUT
ON
EACH GATE MUST
BE
LOW
/ CURRENT PATH
TRACER
WILL
LIGHT HERE
BUT NOT
ON
OTHER GATES
Figure
2.
Wire-AND Node Fault
Page
4
ONE
INPUT
{
MUSTBELOW
--------~
I
9
Figure
3.
Gate-to-Gate Faults
CURRENT
TRACER
LOGIC
PULSER
Model
547A
Page
5
Solder Bridge/Cable Problems
When checking printed-circuit traces which may
be
shorted
by
solder-bridges
or
by
other
means, start
the
Current
Tracer at
the
driver·
arid'
'fonow
the
trace. Figure 4 shows an example of an incorrect
current
path
due
to
a solder-
bridge.
As
the
tracer
probe
follows
the
trace from gate A toward gate
B,
the
indicator remains lighted until
it
passes
the
bridge. This
is
an indication that
the
current has found some path
other
than
the
trace. Visually inspect this
area for solder-splashes, gold-bridges, etc. These principles also apply when troubleshooting shorted cable
assemblies.
H A
H.----
H c
ADJUST CURRENT
TRACER HERE
~
CURRENT PATH
Figure
4.
Solder-Bridge in Printed-Circuit
Multiple Gate Inputs
Another type of
IC
nodal structure
is
the
one-output
multiple-input configuration. Figure 5 shows this type of
circuit being pulsed by a signal
on
gate A's input.
In
this case, place
the
Current Tracer's tip
on
the
output
pin of gate
A and adjust
the
sensitivity control until
the
indicator light just comes
on.
Then check
the
input pins of gates B
through
E.
If
one
of
the
input pins
is
shorted, that pin
will
be
the
only
one
to light the indicator.
Should
the
tracer
fail
to light when placed next
to
gate A's
output,
it
is
a good indication that
the
problem exists
in
gate
A.
To be sure that this
is
true,
use
the
Pulser
in
the manner described
under
Gate-to-Gate
Faults. If the circuit
has no input signal
to
excite
the
node,
use a
logic
Pulser to excite
the
circuit.
H A
Figure
5.
Multiple
Gate Inputs
Modei547A
Page
6
CMOS
and
ECL
Circuits
Troubleshooting
CMOS
and
ECL
circuits
is
performed
in
the
same
manner
as
troubleshooting
TTL
circuits.
The
only
difference
is
in
the
voltages available for
the
Current
Tracer's
power
supply
connections.
The
following
table
shows voltage
range
from
each:
Circuit
Typical
Voltage
Supply
Range
CMOS
3V
to
15V
ECL
-5.2V -
OV
TTL
OV-
SV
CAUTION
THE
VOLT
AGE
PRESENT
ON
THE
BLACK
POWER
SUPPLY
LEAD
IS
ALSO
PRESENT
ON
THE
TRACER'S
ANODIZED
ALUMINUM
CASE.
DO
NOT
LAY
THE
TRACER
ON
ANY
GROUNDED
AREA,
SUCH
AS
AN
INSTRUMENT
CHASSIS.
DAMAGE
TO
THE
POWER
SUPPLY
MAY
RESULT.
These
are
differences in potential
and
the
Current
Tracer's supply voltages may use
both
negative
and
positive,
e.g.,
Voo
= +BV; Vss = -BV.
The
Current
Tracer
is
compatible
with
TTL,
CMOS,
and
ECL
circuits
and
operates
on
supply voltages from 4.5V
to
18V.
Connect
the
Current
Tracer's black lead
to
the
more
negative supply line (Vssl
and
the
red
lead
to
the
more
positive line
(Vool·
THEORY
OF
OPERATION (Refer to Figure 9 Schematic)
CURRENT-STEP
SENSOR.
The Current-Step
Sensor
comprises a pickup core and winding, and eddy-current shield.
The signal to be traced
is
sensed
by the pickup winding and core.
VARIABLE-GAIN
PREAMP.
The Variable-Gain Preamp consists
of
Q1
and peripheral components. The signal from
the Current-Step-Sensor
is
fed directly to the
base
of
Q1. The output
of
Q1
is
taken directly
to
U1.
GAIN-cONTROL
NETWORK.
The gain
of
the Variable-Gain Preamp
is
controlled by ac-coupling the emitter
and
collector
of
Q1, via capacitors
C4
and C5, to the current-controlled variable resistance presented by diode pairs
CR4-
CR6,
and CR5-CR7.
Each
end
of
each diode pair
is
returned to signal ground
or
one
of
the
ac
grounds formed by
capacitors C6, C7, and
CB.
Diodes
CR1, CR2,
and
CR3
determine the control current for the diode pairs.
The
Gain-
Control Network adjusts the gain
of
the Variable-Gain Preamp from -40 dB to +20
dB
with essentially constant,
high bandwidth.
FIXED-GAIN
AMPLIFIER.
U1
serves
to increase the output
of
the Variable-Gain Preamp. lnterstage ac-coupling of
U1
is
effected via
R12
and
C10.
AMPLIFIER
AND
BIPOLAR
PEAK
DETECTOR.
The output
of
the Fixed-Gain Amplifier
is
ac-coupled through
C12
to
amplifier
U2
which provides additional gain. The output
of
this amplifier
is
internally coupled
to
a bipolar peak
detector
(p/o
U2)
where a pulse
of
either polarity results in rapid charging
of
C14.
This
charging signal, a positive,
stretched version
of
the input,
with
an
amplitude proportional to the input, discharges through
R20.
2ND
PEAK
DETECTOR.
The
output
of
the Bipolar
Peak
Detector
is
fed into another peak-detector consisting
of
an
operational-amplifier
(p/o
U3),
with
an
additional
stage
in the feedback loop
(p/o
U2). When the signal on
C14
is
positive,
C15
is
rapidly charged by U2 until the inputs to the operational-amplifier
are
equalized. The charge on
C15
slowly discharges through
R18,
stretching the input pulse for sufficient time to light the indicator lamp.
Model
547A
Page
7
DC
AMPLIFIER
AND
DISPLAY
DRIVER.
The signal at
C15
is
de-coupled
to
this
amplifier,
which
consists
of
an
operational-amplifier
(p/o
U3) and series-pass transistor Q3. The gain
is
set by
R25
and
R27;
C19
is
provided to
suppress oscillations.
MAINTENANCE
PROBE
DISASSEMBLY.
To disassemble
Current
Tracer, refer to Figure 6, and proceed
as
follows:
1.
With
fingers, unscrew (ccw) the plastic indicator light
window
(MP4).
2.
Slide the
bottom
shell
off
probe
tip
end (MP1).
3.
Lift the
top
shell
off
the
probe
(MP2).
4.
Carefully separate the
circuit
board and cable assembly.
PROBE
ASSEMBLY.
Reverse disassembly procedure.
ITAUTION
BE
CAREFUL
WHEN
REPLACING
PARTS
ON
THE
FRAGILE
PRINTED-CIRCUIT
BOARD.
EXCESS
HEAT
CAN
RUIN
THE
BOARD.
USE
A
LOW
WATTAGE
SOLDER-
ING
IRON
(~25
WATTS)
AND
APPLY
THE
MINIMUM
HEAT
NECESSARY
TO
UNSOLDER
THE
LEADS.
PREVENTIVE
MAINTENANCE.
No
periodic
adjustment
or
preventive maintenance procedures are necessary
for
the
Current
Tracer.
ADJUSTMENTS.
Potentiometer
R21
is
the
only
maintenance adjustment in
the
Model
547A. This
trimmer
may be
used
as
a supplementary adjustment
to
the gain
control
(R3)
and
as
a
troubleshooting
adjustment. Refer
to
infor-
mation adjacent
to
the schematic diagram. Preliminary adjustment
of
R21
is
made by setting the
wiper
arm ap-
proximately
midway
in its range.
If
this setting results in
too
little
or
too
much
sensitivity,
with
R3
set
at the 1 rnA
end,
then
R21
can be adjusted
to
correct
this. To assure there
is
1 rnA in the test
circuit-
refer
to
Figure
7.
//!
MP4 MP3
MP5
MP6 TIP COVER
IS
NOT SHOWN
REAR VIEW
FRONT VIEW
---.MP2
~MP1
Figure 6. Exploded View
of
Current
Tracer
Modei547A
Page
8
PERFORMANCE
TESTS
The
following
performance
tests validate
the
dynamic range specifications
of
the
S47A.
Equipment required
is
listed
below:
Equipment
List
for
In-Cabinet
Performance
Tests
Instrument
Required
Characteristics
Recommended
HP Type
Pulse Generator Single shot
up
to
10
MHz
SOV,
1
Amp
HP
1915A
Power Supply 0-20
Vdc,
Current
limiting
at
7S
mA.
HP
6823A
Decade
Attenuator
40
dB
HP
3SSD
1
son
±1%, 0.5W 0811-0592
1
son
±5%,
20W
0819-0022
Minimum
Current
(1.0 mA)
Performance
Test
Equipment Required:
a)
HP
191SA
Pulse Generator.
b)
HP
3SSD
Decade
Attenuator.
c)
HP
6823A Power Supply.
d)
son,
1/2W
Resistor.
CAUTION
USE
A CURRENT-LIMITED POWER
SUPPLY
(75 mA),
TO
PREVENT
DESTRUCTION
OF
TRANSISTORS
Q2
AND
Q3,
DIODE CR8 AND COIL L1
IN
EVENT
TEST
PROBE
SHOULD ACCIDENTLY
SLIP
AND GROUND POINT
"A".
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