Orban OPTIMOD 8400 - TROUBLESHOOTING IC OPAMPS

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TROUBLESHOOTING Orban Model 8400
I) Click the “Advanced…” button on the “Internet Protocol (TCP/IP)” Window.
J) In the “Advanced TCP/IP Settings,” select the “General” Tab; make sure that no check
boxes are checked.
K) Click “OK” to dismiss the “Advanced TCP/IP Settings” window.
L) On the “Properties” window for “Optimod 8400 – Modem,” click the “Advanced” tab.
Make sure the “Internet Connection Firewall” setting “Protect my computer and net-
work by limiting or preventing access to this computer from the Internet” is un-
checked.
If you don’t turn this feature OFF, then data on the 8400 does not get sent back to
your computer. Thus, no meters appear, and the input type and station ID are miss-
ing.
M) Click “OK” to dismiss the window whose name is your new connection.
N) Restart your computer. (This resets the serial port and reduces the likelihood that you
will encounter problems connecting to the 8400.)
Troubleshooting IC Opamps
IC opamps are operated such that the characteristics of their associated circuits are essen-
tially independent of IC characteristics and dependent only on external feedback compo-
nents. 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 probably 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 (–) input, 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
8400'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 pa-
rameters appear to drift excessively, freeze-spray may aid in diagnosing the problem.
Freeze-spray is also invaluable in tracking down intermittent problems. But use it spar-
ingly, because it can cause resistive short circuits due to moisture condensation on cold
surfaces.