HP PageWriter XL M1705B Service Manual page 134

Note ,I
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When dealing with noise problems, remember that most noise is the
result of faulty operator technique or poor quality electrodes. If noise
persists after checking the electrode placement and other elements of
operator technique, the noise may'be the result of faulty leadwires.
Only when you eliminate technique and leadwires as the causes of the
noise should you. consider replacing the patient module.
The leadwire status indicators on the patient module and the
leadwire shorting plugs can be used as a troubleshooting aid. With
the SAECG patient module, these indicators are only active until the
Isrartl key is pressed.
Troubleshooting 6-11