Zeiss humphrey HFA II-i series, Field Service Manual

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Humphrey Field Analyzer II - i Troubleshooting
Confidential and Proprietary
52235C1105 5 - 5
Field Service Guide
6)
Substitute the Failing Assembly.
Once you have deduced which assembly is at fault, or is suspected to be at fault, it
should be substituted with a known good assembly.
7) Confirm the Repair.
After an assembly is replaced, confirmation should be made by reinstalling the failing
assembly to witness the original symptom. You are then assured of the effectiveness of
the repair, and of the need to utilize your spare assembly. Also, the number of
No
Problem Found PCBs returned to the Repair Center is greatly reduced.
Confirming the repair to the customer often helps to bolster confidence in your abilities.
To avoid repeat service calls it is especially important to confirm intermittent problems.
Time spent confirming a repair is time well spent.
Note ­ If the problem still exists, reinstall the original assembly that you removed,
then continue troubleshooting.
Solving Solid Failures:
It is usually straightforward deductive logic or electrical checks that will lead you to replace
the faulty assembly. After replacement of the assembly in question resolves the symptom, it
is imperative that you
CONFIRM THE REPAIR by reinstalling the original assembly and
witnessing the original symptoms again. For many assemblies this is the only means of
positively verifying that the replacement circuitry has resolved the problem.
Solving Intermittent Duplicable Failures:
These failures are resolved in the same manner as solid failures but always require more time
to resolve and confirm. The frequency of the problem helps you determine how long it will
take to verify a repair. A good rule of thumb when troubleshooting intermittent problems is:
2 times the frequency of the symptom gives an 80% confidence level of the repair.
EXAMPLE:
Problem: The problem appears only about once an hour. The sequence
of events needed to reproduce the problem leads you to
believe a circuit board is the likely cause.
Solution: The suspected circuit board is replaced. To provide an 80%
confidence level that the circuit board resolved the problem, the
instrument will need to be tested for 2 hours without failing.