Service Model 8903B
SIGNATURE
ANALYSIS
8-29.
SIGNATURE
ANALYSIS
Signature analysis is a simple method of verifying the operation of digital circuitry. When properly used, signature
analysis can detect extremely subtle hardware faults. Signatures must identically match those given in the signature
tables.
If
everything is working correctly, signatures will all match exactly.
If
they don’t match, by even one digit,
something is wrong.
The Keyboard and Display, Latch, and Counter/Controller Assemblies (Al,
A7,
and
A8)
are designed for
troubleshooting with signature analysis. Signature analysis
is
a method of digital signal tracing using
test
routines
programmed in the Audio Analyzer’s
ROM.
With the Audio Analyzer’s Controller executing the signature analysis
routine, the signature analysis routine, the signature analyzer’s test probe is used to check nodes
in
the circuit
under
test.
The signature analyzer converts the signals at the node into a four digit “signature”, which
it
displays.
This signature
is
then compared
to
the signature in the troubleshooting checks adjacent to the appropriate
schematic. These two signatures must be identical.
Signature analysis can be speeded up
if
the following considerations are kept
in
mind
1.
Make sure that every step is performed
as
described in the set-up procedure. That is, make sure that the
2.
Double-check to ensure that the signatures are being taken at the correct node.
3.
Make sure that the signature analyzer probe
is
making good contact with the pin being checked. Oxidation
4.
When you think that you have found
a
bad signature, double check
to
make sure.
5.
When checking a node, be sure that the unstable signature indicator
is
not blinking.
clock,
start,
and stop connections and triggering are correct.
on pins can cause invalid signatures due
to
poor contact.
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8-20
reu.20JUN87
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