5518-FM DIGITAL
TROUBLESHOOTING
5-11
Troubleshooting IC Opamps
IC opamps are operated such that the characteristics of their associated circuits are
essentially independent of IC characteristics and dependent only on external feed-
back components. The feedback forces the voltage at the (–) input terminal to be
extremely close to the voltage at the (+) input terminal. Therefore, if you measure
more than a few millivolts difference between these two terminals, the IC is proba-
bly bad.
Exceptions are opamps used without feedback (as comparators) and opamps with
outputs that have been saturated due to excessive input voltage because of a defect
in an earlier stage. However, if an opamp's (+) input is more positive than its (–) in-
put, yet the output of the IC is sitting at –14 volts, the IC is almost certainly bad.
The same holds true if the above polarities are reversed. Because the characteristics
of the 5518's circuitry are essentially independent of IC opamp characteristics, an
opamp can usually be replaced without recalibration.
A defective opamp may appear to work, yet have extreme temperature sensitivity. If
parameters appear to drift excessively, freeze-spray may aid in diagnosing the prob-
lem. Freeze-spray is also invaluable in tracking down intermittent problems. But
use
it sparingly,
because it can cause resistive short circuits due to moisture condensation
on cold surfaces.
Technical Support
If you require technical support, contact Orban customer service. See
http://www.orban.com/contact/
for contact information. Be prepared to describe the
problem accurately. Know the serial number of your 5518
this is printed on the
rear panel of the unit.
Please check Orban’s website,
www.orban.com
, for Frequently Asked Questions and
other technical tips about 5518 that we may post from time to time. Manuals (in
.pdf form) and 5518 software upgrades will be posted there too — click
“Downloads” from the home page.
Factory Service
Before you return a product to the factory for service, we recommend that you refer
to this manual. Make sure you have correctly followed installation steps and opera-
tion procedures. If you are still unable to solve a problem, contact our Customer Ser-
vice for consultation. Often, a problem is relatively simple and can be quickly fixed
after telephone consultation.
If you must return a product for factory service, please notify Customer Service by
telephone,
before
you ship the product; this helps us to be prepared to service your
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