Chapter 4 Assembly Level Troubleshooting 73
Inguard Controller The inguard controller controls the measurement process. It receives
function and range data from the outguard and then sets the appropriate
switches in the inguard. The inguard controller also controls the operation
of the A/D converter.
Assembly Level Troubleshooting
3458A Failures To troubleshoot the 3458A, first determine what the failure is. Then use the
information in the following paragraphs to determine the defective assembly.
Failures can show up in a variety of ways. Some failures are obvious, like a
completely inoperative instrument or a self-test failure. Other failures may
only show up during the performance tests. Others yet will only show up
under certain conditions, like the instrument working from the front panel
but not from remote, In most cases, the 3458A failures can be separated into
the following major categories.
1. Turn-On Failures - these failures are as follows:
a. 3458A Inoperative with Blank Display
b. 3458A Inoperative with Unintelligible Messages in Display
c. Isolator Failure
d. RAM Failure
2. Self-Test Failures - these are detected during the 3458A's self-test.
3. Performance Tests Failures - these are detected during the 3458A's
performance test,
4. Miscellaneous Failures - these failures are as follows:
a. GPIB Failure (Self-Test passes)
b. Ext Out Failure
c. Ext Trig Failure
d. Fan Inoperative
e. Long Term Stability Failure
Turn-On Failures These failures normally show up when the instrument is first turned on and
it attempts to go through its power-on self-test. The following paragraphs
explain these failures and how to troubleshoot them.
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