User manual

19
General Troubleshooting Tips
Systems operating in failure mode can behave in very strange ways! The situation is not
“normal” and the goal is to figure out why. It’s important to examine the conditions and
think about the problem before blindly diving in. What combination or conditions could
create the condition I am observing?
Digital voltmeters DVM are wonderful tools, but they can mislead. A voltmeter draws a
tiny amount of power from a circuit. You may in fact have a very poor connection or even
a “sneak circuit” which may mislead you. A 12 volt test light can be very useful because it
“loads” the circuit.
The ohmmeter function of a DVM can only be used on dead circuits. At best, you won’t
get the correct results and at worst, you will ruin your meter. There may be residual
energy or capacitors present which can really be confusing.
Measuring a diode requires enough voltage to activate the diode, the ohmmeter function
may not provide enough voltage to do this. Many DVMs have a diode check function just
for this purpose.
With all the plastic, paint, dirt, corrosion etc, it can be difficult to make a connection. Be
sure you really have a connection!
Most meters come with needle probes, which are fine, but you have to “hold” both of them
in place to make a measurement. Don’t limit yourself to the probes; accessories like
alligator clips and jumper leads can make life much easier and safer!
Yes 12 volts won’t cause a shock, but the current can burn wires can destroy components
in an instant. A temporary test connection might create other problems, so consider
carefully what you are trying to do.
Both voltage and current are required to do the work of lighting a lamp, running a motor or
charging a battery. Knowing both the voltage and the current will speak volumes about
what is really occurring. If voltage is present and current is flowing, work is being done
and that work might be heat!
Measuring current in DC system usually requires that the circuit be broken to insert a
current meter. A clamp-on DC amp-meter makes this unnecessary. Make sure the meter
you buy makes both DC and AC current measurements.
Clamp on DC amp-meters can be fickle devices and are not terribly accurate. They are
sensitive to stray magnetic fields and must be “zeroed” when you use them. They
typically don’t measure small currents very well.
Make some measurements when things are operating correctly and verify that you get the
results you expect.