User & Service Manual
Xltek EMU 128 Headbox
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simultaneously, but only one Digital Board at a time sends data to the computer. This is
fundamental to serial communication. Signals HSFS, HSSCK and HSSDAT are used
(U11-18, U19-11, U19-8).
If a sine or square wave Channel Test signal is commanded, the PIC writes a scaled
value from a lookup table to Digital-to-Analog Converter (DAC) U18 at each sample time
(signals DADAT, DALD, DASTB). Precision voltage reference U12 establishes the
full-scale DAC output. Together with the intrinsic very high accuracy of the DAC, this
gives amplitude accurate to a fraction of a percent.
Patient Event Switch closures are detected by the PIC on Port B4 (U11-41). Only the
Digital PCB for Channels 1-32 detect Patient Event Switch closures.
Servicing
We do not recommend that the owner try and repair the equipment, because the factory
is better equipped for servicing. The factory has proper equipment to test the patient
safety isolation barrier for 4KVAC dielectric strength after re-assembly. The following
guidance is provided for the extreme case in which a repair is urgently required.
The usual diagnostic methods apply, narrowing down from the general to the specific.
For example:
1. Inspect the cables and connectors.
2. To make sure the problem is in the headbox, not the computer, connect another
EMU128 or an EEG32 to the NeuroWorks computer.
3. Find out which board assembly has failed.
Problems Starting a Study
The circuit description of the Digital Motherboard explains how to distinguish a failure on
the Motherboard from a failure on a Digital PCB when a study fails to start. To diagnose
which Digital PCB has failed, probe U21-6, HSATX, and U100-2 to see if the commands
are getting through, then U17-2, HSARX, for the replies. Since the baud rate is 19.53K,
a good timebase setting for the oscilloscope is 250
µ
s. Make sure to connect the probe
ground to the correct side of the patient isolation barrier. If the study starts but the scroll
bar doesn’t move across the screen, there is a problem with the digitized waveform data
and those signals should be probed. Start from the Digital Motherboard and work back
through to the Digital PCBs.
Problems with Signal Quality
If there is a missing or bad signal, first try swapping cables to the Breakout Box. If you
are still experiencing problems, try running a channel test.
Run a Channel Test
1. On the montage settings toolbar, set
LFF
to 0.1 Hz.
2. Choose
Controls
->
Channel Test
. The Channel Test control bar appears above the
waveform display.
