STAR*TECH
0
Journal
Enzo's
April 1997
Tech
Tips
"Hey Enzo, I can't find the self-test button on this Captain Fantastic!,,
Douglas 'Enzo' Mccallum• Shiawassee Technical Services• Lansing, Ml
SETTING UP A Co1N-OP SERVICE BENCH (PART
5)
Unless you haul all your service needs to someone else, you must have a ., shop for
maintenance and repair of equipment. Depending upon your needs. the size of your,
and the thickness of your wallet; your shop could be anything from the gaiI11l.ge to the
house on up to a huge professional facility. Whatever league you are in, the workbench is
an Important part of the shop. Here are some consld~rations for setting up a service bench.
EQUIPPING THE BENCH: SELECTING AN o~sCOPE
Let's go shopping for a good os-
cilloscope. As we said before, you
don't need a rocket-to-Mars,
nuclear power, Star Trek kind of
'scope, just a good one. There are
a number of considerations:
single or dual trace (or more),
bandwidth, sensitivity, digital or
analog, new or used.
Oscilloscopes are made to serve
in a wide variety of situations.
Most of our 'scope applications
are pretty basic, we aren't doing
lab research. Whether line fre-
quency or high frequency from
a switcher or monitor flyback, we
use a 'scope to look at power sup-
ply ripple (and level). We look at
real world control signals, such
as switch matrix strobes or score
display digit select and segment
lines in a pinball. We view the
various signals in a video moni-
tor, the vertical and horizontal
sweep sections, and the color and
sync sections, and power supply.
We look at audio in most any-
thing. Of course we look at logic
board signals. That is probably
the most demanding of our ap-
plications. Even so, we don't re-
ally need an extra fancy 'scope.
Get what you need, don't go nuts.
You really should have a dual
trace model. More than that is
overkill, and it isn't all that easy
to even find a single trace 'scope.
You will only use one of the traces
the majority of the time, but there
are situations that require watch-
ing two signals at once. Sensitiv-
ity isn't much of an issue for us.
Fancier 'scopes go down below
even 1 mv per division, which is
to say that even a signal as small
as 1 millivolt can be seen as large
as one division of the lines on the
screen. We seldom run into
meaningful signals this tiny. The
smaller the signal you can view,
the more the 'scope costs.
Frankly I prefer more range on
the top end, lOV / div. instead of
only SV /div., for viewing the
high voltage waveforms in moni-
tors.
Bandwidth, measured in MHz, is
a measure of more than how high
a frequency the 'scope can dis-
play. Even with a slow clock
speed like 4MHz, the waveforms
in digital circuits are square