Zenith ZVM-1240 Service Manual page 29

YOUR WAVEFORM MAY LOOK DIFFERENT
Differences in oscilloscope probe ground lead length
and ground' lead positioning may explain why your
waveform and the photographs in this manual look dif-
ferent.
Pickup of stray signals add to the test circuit signal,
giving a distorted display and wrong peak-to-peak volt-
age. The stray signal is picked up in the ground lead
of the oscilloscope probe. For the least pickup, keep
the probe ground lead as short as possible and keep
it away from strong magnetic fields.
FigureS
Short Ground Lead
Waveform Photograph Explanations
Both photographs (Figures B and C) below show the
same test circuit signal, under the same conditions ex-
cept for ground lead length and positioning. The photo-
graph taken with the short probe ground lead shows
no distortion and correct peak-to-peak voltage. The
photograph taken with the long probe ground lead
shows distortion and an incorrect peak-to-peak volt-
age. (Pickup in this case. is from the horizontal output
transformer of a monochrome monitor).
Also, your waveforms can vary slightly from the photo-
graphs in this manual due to bandwidth, input imped-
ance, and other oscilloscope differences, as well as
the monitor being different.
FigureC
Long Ground Lead
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