Service manual

Troubleshooting
Revised 2/18/05 6-19
Flat Line Data Problems
Flat line data problems are often caused by incorrect
parameter settings, loose connections, or static
electricity damage to the amplifier inputs (in cold dry
climates).
On the VikingQuest amplifiers, make sure the amplifier
switches are pressed in.
Run the USB/Firewire Diagnostic AutoTest and
amplifier/headbox tests.
With system power off, disconnect and reconnect the
external cable connections. Verify correct sensitivity
and filter settings. Increase the amplifier sensitivity
(SNS) setting and try recording. Try this step a few
times. If the new setting displays curve data, the
problem was an incorrect parameter setting.
For the Vikings, enter the free run EMG mode and run a
calibration pulse for each channel.
If a single channel, or set of channels consistently
display a flat line, suspect the headbox, headbox cable,
or amplifier module. There may be a loose or broken
connection in the headbox/amplifier signal path or static
electricity may have damaged the affected amplifier
channels.
If all channels are affected, the problem may be caused
by the amplifier, amplifier cable, or a problem in the
base unit.
Troubleshooting Noise: Equipment Checklist
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Items to check Detail
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1. Check the live signal (View Input mode). If noise is
locked in place on the waveform or seemingly
triggered from one place on the waveform screen,
change the stimulator rate to an odd number to avoid
time-locking the sweep to 50/60Hz noise.
Adjust the stim rate until the signal rolls on
the screen. This will be averaged out over
time. Use an odd number, such as 10.3 or
11.1 stimuli/sec. for an ABR; 4.7 or 5.1 for a
VEP.
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2. Check the impedance of surface electrodes. For
evoked potential studies; electrode impedances
should be below 5Kohms and matched within
1.5Kohms. For the O.R., look for a good balance
under 30Kohms.
DO NOT check impedances on concentric
needles or ring electrodes.
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3. In most applications, do not let the stim rate exceed
the acquisition window (timebase).
Formula: (1/[Stim Rate]<Timebase
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4. Short the recording electrodes together temporarily
in free run EMG mode, or in View Input mode.
If the noise disappears, the amplifier is OK,
and the problem is most likely electrode-
related.
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5. If 50Hz/60Hz noise is suspected, measure the time
interval between consecutive peaks with your
cursors.
20ms = 50Hz noise
16.6ms = 60 Hz noise
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6. If in the O.R., run a baseline before you start the
surgery to verify proper system operation.
Perform the baseline test before other
equipment is powered up.
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7. Put a loose knot in the power cord to disrupt the
possible antenna effect.
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8. Orient the computer/cart/amplifier in different
directions and watch for changes in noise levels
Rotate, or move the amplifier around the
room.
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9. Try rotating the patient’s chair 90 degrees.