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1
REPAIR
BY SIGNATURE
ANALYSIS
1.
GENERAL
For
repair
by
signature analysis
a
testrom
has
been
developed.
This testrom enables the
user
to
test
the
digital
part
of the
PM2521
by means
of signature
analysis.
It
also
enables troubleshooting
at
component
level in
the
circuit
under
test,
by comparing
the
actual
signature
to the
correct one.
So
the trouble-shooter
can
trace
back
the faulty
node.
In
total
there
are
8
tests. In
the testrom 7
tests
have been
implemented and one
test
is
made
with
the
help of the
free
run
facility
of the
PM2521
.
2.
WHY
USE
A
SIGNATURE
ANALYSER
?
Thanks
to
the
microcomputer
in
the
digital
part
of the
PM2521
,
the instrument can be very
small.
Due
to
this
the bus
structure
is
very
complex. Data flow on
the
bus
becomes complex
and cannot be
analysed
with an
oscilloscope
and
voltmeter
any
longer.
Therefore
the
need
to
test
and
service
the
digital
part
is
acute.
The
trouble-shooting
involves
the detection of
circuit failure
and
the
localization
of
faults
at
the
source.
Finding the
fault
source
in
a
bus system, such
as
the bus
in
the
PM2521
,
with
complex
feedbacks can be
difficult.
But opening
the feedbacks paths
and
using
the
signature analyser
makes
fault-finding
easy.
3.
CHECKWITH A
SIGNATURE
ANALYSER
The
signature analyser
checks the
digital
part
of the
PM2521
by
detecting the
bit
stream
at
various
circuits
nodes,
and
displaying
them
as
hexadecimal
signatures.
To do
this
the
PM2521
supplies
the
signature analyser
with
three gating
signals,
or
in
some
cases four:
START,
STOP,
CLOCK
and
QUALIFIER.
START
signals
the beginning of
a
measurement and
prepares the signature analyser to
recieve
information
from
the data probe.
STOP
closes this
measurement.
In
cases of
measuring
signatures
with
RC
delays,
a
QUALIFIER
has to
be used to stop the
incomming
information
for
a
short period of time.
The
CLOCK
is
the
system
clock of the
PM2521
under
test
to accept the data synchronously.
NOTE:
The
active
edge of each
of
these gating
signals
must
be
selectable.
4.
TYPE OF SIGNATURE
ANALYSER TO
BE USED.?
The
signature analyser to
be used
in
combination with
the
PIV12521
should have the following
capabilities:
—
Selectable edges
of;
START, STOP
and
CLOCK
- AQUALIFIER
—
Signatures
in
the following sequence:
DIGIT
DISPLAY
DIGIT
DISPLAY
0
1000
8
1
1001
9
1010
A
:B
1
1011
C
1100
F
1101
H
B
^^B
1110
P
B
^^B
1111
U
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