146 Chadwick-Helmuth Company, Inc.
Chapter 6 - Maintenance
6.4.1.2 Clearing the Fault Log
In some early versions of the Vibrex firmware, the fault log fills and begin
to corrupt the working power of the processor. In such cases, it is
necessary to manually clear the fault log; clear the fault log, as follows:
1. Press and continue to hold down the
0 (zero) key.
CAUTION: Never clear the fault log without first printing it out, if
possible. It is important that you keep a record of this data.
2. Press the
ON key until the power-up, self-test screen displays.
3. Release the
0 key.
Also, the user may turn the unit on and press
0 during the power-up test.
Keep in mind that, if you clear the fault log without printing it, and
clearing doesn't fix the problem, there is no data left to help troubleshoot
the instrument. If you call Product Support, sending or faxing us a copy of
the fault log is most helpful in determining the cause of a problem.
6.4.1.3 Failure Modes
Basically there are three failure modes that prevent the Vibrex unit from
acquiring a reading, as listed in the fault logs. These modes are
Azimuth Unstable - Means the Vibrex unit is not getting a steady one-
per- revolution signal from the photocell. This problem could be
happening because the photocell is clipping the tape in two spots, is
proxing (getting returns from a shiny surface), or has failed (rare).
No Azimuth - Is caused by using too little tape to register (obvious,
because the Vibrex unit acquires data at lower RPM but quits working
as the RPM increases), also there could be no tape, the tape has not
been applied in the beam, or there is an open in the photocell wiring.
Vibration Unstable - Is caused by unstable vibration characteristics. This
problem could be resulting from a poor location (flimsy mount) or a
loose mounting structure supporting dynamic components on the
aircraft. It can also be caused by another component turning at or near
the same rate as the component being measured, such as unbalanced
tail rotor shaft that interferes with the tail rotor balance. Normally a
spectrum examination will reveal this problem.
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