Tektronix 7A42 Instruction Manual page 9

signature on this driving device; if it matches the
signature on the bad input, go to step 11. In this
example, assume that the signature at A6U530 pin
12 was incorrect (not H9C6). The source node for
this input is A6U530 pin 2 (the same IC).
If the signature on the driving node (A6U530) does
not match that of the driven node (A6U530 pin 12),
proceed as follows:
a. Check for an open run on the board or in a cable,
or for a loose connector. Check any cables
pertinent to the node in question, then recheck
the signatures.
b. Check for noise induced by the high currents
caused by shorted signal lines. These currents
can produce transients which will affect the
signature analyzer's interpretation, depending on
where the signature analyzer's probe is grounded
and the layout of the circuit board. These
problems must be troubleshot by other means.
11. If the signature at the driving node (A6U530 pin 2)
matches the incorrect signature at the bad input
(A6U530 pin 12), we turn our attention to the driving
node. If there is no entry in the REFERENCE?
column for this input pin, the signature table for the
driving IC can be found among those in the test you
are now running (SA Test #23). In this example, the
driving IC is a gate in the same package (A6U530).
NOTE
The meaning of the letters Y, N, and P in the
REFERENCE? column (next to the INPUT'S
SOURCE NODE) is as follows:
Y - Additional troubleshooting information
is listed at the bottom of the page. This may
be a reference to another signature analysis
test, or to other documented troubleshooting
procedures.
N - This INPUT'S SOURCE NODE is at the
boundary of a major functional block,
beyond which signature analysis is not
useful. The source may be an analog circuit
that is better tested by other means. Refer to
the appropriate troubleshooting procedure
for that circuit in the Maintenance section of
Volume 1.
General Informatlon-7A42 Volume 2
NOTE
P - This indicates that the INPUT'S
SOURCE NODE is a pseudogate, that is, part
of
a
wired-AND or wired-OR structure. A
table next to the signature table lists all the
components in the structure. All inputs to
each gate in the list can affect the output of
the pseudogate. Signatures must be checked
at the appropriate inputs of each involved
gate. A diode can be checked with signature
analysis as if it were a gate with one input
(anode) and one output (cathode).
12. In this example, the Output Setup given in the
Signature table for A6U530 is number 1, which was
implemented previously. Proceed down the Output
Pin 2 column to the first arrow. Ensure that the
correct Input Setup (number 1 again) has been
made, and check the signatures at each node in the
WIREAND 7 list (they should match and be wrong).
If wrong and matching signatures are present,
locate the signature table for each component in the
WIREAND 7 list and check the appropriate inputs to
locate the problem. If all the input signatures are
good, the Trigger Troubleshooting part of the
Maintenance section in Volume 1 outlines some
special techniques for troubleshooting pseudogat&
nodes.
13. If the signature at A6U530 pin 4 is correct (it should
be 8P54), check the Signature of the next input
designated with an arrow, A6U530 pin 5. This input
comes from another pseudogate, WIREAND 6.
Proceed as before until the problem is solved.
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