39
When possible, power the LC103 with the PA251 AC
Power Adapter connected to a properly grounded AC
outlet. The PA251 Power Adapter maintains the third
wire ground shield and keeps the noise away from the
measuring circuits inside the ReZolver.
Interpreting Capacitor Value Readings
The LC103 ReZolver automatically displays the three
most common capacitor values of picofarads (pF),
microfarads (uF), and Farads (F). When measuring
capacitors with the LC103, you may encounter some
capacitors with a value marked without a decimal, such
as “25000 pF”, but that read “.0250 uF” on the LC103
display. You may also encounter, as an example, a
capacitor which is marked “3300 pF” by some
manufacturers, yet an identical replacement is marked
“.0033 uF” by another manufacturer.
As these examples illustrate, capacitors can be marked in
pF, uF or even F. A fourth value multiplier, the
nanofarad (nF) is seldom used to mark a capacitor, but is
used occasionally in design and industry. Table 11 will
help you to easily convert from one reading to another.
Change To
From
Farads Microfarads
Nanofarads
Picofarads
Farads
Move decimal 6
places right
Move decimal 9
places right
Move decimal
12 places right
Microfarads
Move decimal 6
places left
Move decimal 3
places right
Move decimal 6
places right
Nanofarads
Move decimal 9
places left
Move decimal 3
places left
Move decimal 3
places right
Picofarads
Move decimal
12 places left
Move decimal 6
places left
Move decimal 3
places left
Table 11 - Capacitor value conversion chart
The In-Circuit Capacitor Test
In many cases it is desirable to test a capacitor
in-circuit and then, if necessary, remove it to test
it more completely out-of-circuit. Reliably
testing capacitors in circuit can be tremendously
time saving. Due to the wide variety of circuits,
there are a few things to keep in mind as you test
capacitors in-circuit.
1.
Many circuits, especially power supplies,
place two or more capacitors in parallel. In
this case, you will see a high capacitor value
reading. This would be normal since parallel
capacitance adds. When the LC103 returns a
capacitor value that is higher than the
capacitor being tested check for other
capacitors in parallel. It may be necessary to
remove the suspect capacitor to test it
accurately.
2.
Sometimes the LC103 will return a value and
ESR reading accompanied by “SUGGEST
REMOVAL.” In this case, there are
components surrounding the capacitor that
have upset the measurements. This capacitor
would be beter tested out-of-circuit.
3.
Some circuits require capacitors with less ESR than
the EIA specifies. When testing these capacitors, the
LC103 may show a “GOOD” reading but the
capacitor may not work in the circuit. Refer to the
manufacturer’s specifications or compare to a
known-good capacitor.
The following flow chart explains how the ReZolver
decides which indicator to display with the value and
ESR readings when performing an in-circuit capacitor
test.
When the In-Circuit Capacitor Test button is pressed the
LC103 begins its parallel component checks. If this test
fails the ReZolver will display the value and ESR
measurements along with the SUGGEST REMOVAL
message. If the parallel component check passes the
LC103 checks to see if the COMPONENT
PARAMETERS have been entered. If so, it will
compare all measurements to these values and will
display a GOOD message along with the value and ESR
measurements if they fall within the specified parameters
or BAD if they do not. If not all of the parameters are
entered the LC103 checks to see which, if any, are.
Depending on which parameters are entered the LC103
sets different defaults to which compare the capacitor
under test. If none of the component parameters are
entered the LC103 defaults to tantalum for measured
values above 1 uF and ceramic for measured values
below 1 uF. The tolerance will default to +/-20% and the
voltage will be 50 V. These defaults do not appear in the
display and are only used by the LC103 to determine if it
will display “GOOD??” or “BAD??”.
Fig. 29: In-Circuit Capacitor Test flow chart.
In-Circuit
Capacitor Test
did either parallel
component test fail?
is value
entered?
are all
parameters
entered?
is ESR high?
is tolerance
entered?
default ± 20%
is measured
value >1
µ
F
is value low?
is value okay?
is type entered?
is value high?
display "GOOD"
display "BAD"
display
"SUGGEST REMOVAL"
YES
YES
YES
YES
NO
NO
NO
NO
NO
NO
NO
NO
NO
YES
is voltage entered?
default tant
display "BAD?"
YES
YES
YES
YES
YES
default ceramic
NO
NO
ESR < limit?
display "GOOD?"
YES
default 50 V
NO
YES
