DCA75 - Frequently Asked Questions (FAQs)
the DCA75 be used in-circuit?
It is not possible to take into account the influence of
other unknown components around the component you're
trying to test and results can be misleading. Also, it
is possible that you may damage your instrument if there
is any unexpected charge in your circuit. We know that
it's not always easy, but we recommend that you test
components that are not connected to other parts.
the DCA75 ok with germanium transistors, can it measure
leakage current and does it take into account the
leakage current for it's gain measurement?
The DCA75 will detect the germanium (or silicon) type of
semiconductor. It will measure leakage current and it
takes that leakage into account when measuring gain
(unlike most multimeter hFE measurements).
noticed the leakage current of my germanium transistor
gradually drop with each subsequent measurement. Is the
battery failing or something else wrong?
current is extremely temperature dependent and
particularly noticeable for germaniums as the current is
fairly high to start with. The leakage current can
double for just a 5°C increase in temperature. So after
some handling, the transistor temperature slowly falls
and can lead to a decreasing leakage current. That's
completely normal and correct. Additionally, DCA75 test
currents are completely independent of battery
Collector and Emitter of my germanium transistor is
showing the wrong way round, is the DCA75 wrong?
the leakage current of the germanium transistor is quite
high (due to warming from your fingers for example), the
DCA75 can reject the "correct" pinout.
However, it will then search for all other device types
and configurations. It can, in those circumstances, find
a transistor with the C-E swapped (although gain can be
very low). Tests in a simple circuit confirm that you
can get a germanium transistor to work, with some gain,
in that way. So the DCA75 is not wrong, it's just found
a configuration that yields a low leakage current. Try
keeping your transistor cool during testing to avoid
the Atlas DCA75 measure Zener diodes?
The DCA75 can test Zener diodes up to around 11V. Zeners
with a reverse voltage of less than around 8V will be
tested at 5mA, higher voltage ones may be tested at a
lower test current. The test current is confirmed on the
I use the DCA75 to match transistors?
The main parameters that you may be interested in are hFE
and VBE. Both of these parameters are
measured by the DCA75. This enables you to group your
transistors that have similar gain figures for example.
Additionally, the use of the curve tracing facility
allows even greater flexibility for your desired
Unijunction transistors (UJTs) supported?
The DCA75 doesn't currently support UJTs although this
is planned for a future release (to be available via
online upgrade too).
MOSFET has a separate "substrate" or
"bulk" connection, what do I do with that
rare MOSFETs have 4 leads (gate, source, drain and
substrate). To enable the DCA75 to test these, connect
the substrate lead to the source lead. If your MOSFET
does not have a body diode then you will also need to
connect a diode across the drain-source leads.
will the DCA75 show if my component is faulty?
the DCA75 would show "No component found".
Sometimes it may still be able to see a pn (diode)
junction within the component you're testing, in which
case it would display "Diode or diode junction(s)".
If there is a short circuit within your component then
the DCA75 will display "Short circuit on RED
GREEN" for example.
my Atlas DCA75 be upgraded online?
The PC software (available
here) will check your instrument to make sure it's
got the latest firmware, it will then offer to upgrade
it for you.
can't the DCA75 analyse triacs or thyristors that need
higher currents than 10mA?
test currents of the DCA75 are deliberately low to avoid
damage to any potentially random component that can be
connected any way round. The Peak
Atlas SCR is aimed specifically at analysing a wide
range of triacs and thyristors that require test
currents from less than 100uA up to 100mA.
voltage regulator won't test out correctly on the DCA75,
are many varieties of voltage regulator available and
some can't be tested on the DCA75. Firstly, the
regulator voltage needs to be around 8V or lower for it
to be testable. Secondly, there are some regulators that
just aren't stable unless they're in their intended
circuit with decoupling caps and a suitable load.
you have software that can run on a Mac or under Linux
don't have immediate plans for releasing non-Windows
software, although we are investigating the possibility.
have a suggestion for a new supported component type or
new feature, what can you do?
love to hear any new component or new feature
suggestions. We're a flexible company and we'll do our
best to implement new features when possible.
the battery used if I'm connected by USB?
The instrument draws all the power it needs from the USB
connection (if present).
long is the warranty period?
our products now have a warranty of 24 months. This
doesn't cover accidental damage or abuse however.