Star Tech Journal

STAR*TECH
March 1997
Journal
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... continued from page 9
plug the transistor into the little
socket on the meter. Not very
convenient for big transistors.
What does gain tell us? Unless we
are matching transistor pairs, not
a whole lot. Most transistors we
work with are in switching cir-
cuits and as such are operating
in saturation. Gain becomes ir-
relevant. Some transistors are
leaky at working voltages but test
good on a meter. These gain tests
won't show this. Transistor test is
not a selling point for me.
Capacitance. These ranges won't
measure leakage, but if a lO0ufd
cap measures 36ufd, then it is a
good bet that it is bad.
Electrolytics are about the only
caps that fail in our equipment.
This means that we need to mea-
sure capacitance above 1 or 2ufd
since we see few 'lytics smaller
than that. Mostly we see caps
with values of 10 to lO0ufd as fail-
ures in monitors, and much,
much larger than that in audio
and power supply circuits. Thus
a meter that measures only up to
2ufd will be of limited value.
Some of the newer models mea-
sure up to 10,000ufd, but not all
of them. Check first.
Frequency counter. The only
thing I use one for is setting the
speed on cassette players and the
oscillator on CD players. I don't
remember a time I needed a freq
measurement in the field. If your
monitor won't sync, what does
the frequency tell you? Crystals
tend to work or not, they don't
usually work at the wrong speed.
There may be a problem with a
clock divider in a logic circuit, but
your scope can find that easily
and chances are you work on
clock divider problems in the
shop, not the field. Most meters
don't go over 2Mhz anyway. Not
a selling point for me.
Other features. Logic level -
maybe, especially if you don't
have a logic probe. Data hold -
lets you probe a circuit and the
meter will hold the reading until
you reset it. Useful when you
can't watch the display and probe
at the same time. I have never
used it. Bargraph or trend indi-
cator - you pretty much are go-
ing to get this anyway. Can't hurt.
True RMS - it can make a differ-
ence, but only on non sine wave
signals. You generally do pay
extra for it. Not important
enough to me. Min/max - you
could leave it on something to
monitor a line and maybe cap-
ture a glitch, but it is mostly in
more expensive models. Limited
value.
Accessories. Often included, the
rubber holster is handy. It not
only offers some protection, but
it also lets you stand the meter in
a more readable position. Tem-
perature probe - I have no use
for it in what I do, I can tell if
something is too hot. If you work
with refrigerated or heated vend-
ing it could be very useful. I sup-
pose you could even check the
hot water in your laundry equip-
ment, although fingers work
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... continued on page 76