EDS LeekSeeker 89R User manual

LeakSeeker 89R AutoRanging Fault Locator OPERATIONS MANUAL
The LeakSeeker 89R is a rework of LeakSeeker 89 designed by EDS and with
permission from Dave Miga ([email protected])
Please read this manual completely before trying to use the LeakSeeker for the first
time. There is a short tutorial on page 7 that will guide you on your way to the “Ah-Hah!”
moment of understanding. Skipping the tutorial will make your understanding far more
difficult.
This unit is designed to be used on a non-powered circuit, as it supplies its own precise
test voltages. Be sure power is disconnected from the unit under test, or your
LeakSeeker may be damaged!
1

PRELIMINARY
The LeakSeeker model 89R will locate a shorted or leaky component or any other
shorted condition (such as a pinched wire or solder bridge) with a short resistance value
from zero to 300 ohms, to the exact spot on a pc board. If the unit has multiple pc
boards, LeakSeeker will first identify which board contains the defective component,
then will guide the technician directly to the location of the defective component on that
board. The LeakSeeker has three sensitivity modes, all fully automatic. Tests are done
simply by touching the solder pads along a “shorted” foil trace and the pad with the
highest pitch marks the defect.
This unit includes a universal AC adapter with a 2.1mm plug. The internal regulator in
LeakSeeker allows it to run from any AC or DC adapter or battery from 9 to 25 volts AC
or DC, as long as it has a 2.1mm plug. It also has prevision for an internal 9V battery for
portable operation.
HOW THE LEAKSEEKER WORKS
The LeakSeeker 89R pinpoints the exact location of a shorted or leaky component by
comparing the resistance at different component solder pads along a shorted pc foil
trace, and subtracts the foil's milliohm resistance from the value of the defective
component. Therefore, there is a different reading at each pad, although by a very small
amount, with the lowest reading at the short. LeakSeeker consists of a 16 bit self-
calibrating digital comparator with a range of zero to 300 ohms, auto memory, and a
variable gain comparison circuit with visual and audible indicators. Initial search for a
shorted component automatically starts at the LeakSeeker's maximum range and
counts down to the resistance of the defective component, within a "window" that is
indicated by nine small distance LEDs. It also uses a variable pitch tone, which will be
at its highest when the test probe is touching the pad where the resistance is lowest.
LeakSeeker can use one of two different test methods to locate the defect. The
NORMAL test causes a precise voltage/current to appear at the test PROBE, and as
the technician touches each pad, the small difference in the voltage/current readings is
translated into the change of the beep pitch and distance LEDs. This test method is
ideal for finding the location of typical “dead” shorts under a few ohms.
The 3-WIRE test is used when the readings are confusing, for example, if the "short" is
actually many ohms, and a large electrolytic capacitor is somewhere along the trace.
Instead of a steady tone, the pitch may constantly change as the capacitor tries to
charge or the leaky defective component warms up, making stable readings impossible.
The 3-WIRE test separates the precise voltage reference REF+ from the PROBE port. It
is more difficult to use, so the technician should have a thorough understanding of the 3
normal testing methods first.
2

FIRST, SOME IMPORTANT NOTES THAT YOU NEED TO REMEMBER:
LeakSeeker recalibrates itself automatically to a new range as you get closer to the
defect, as ohms get lower. If you get further from the short and resistance goes higher, a
lower pitch of the tone, and eventually no tone at all and the lowest red indicator will be
the only indication. If you loose your way, or accidentally touch the wrong pad, you can
push RESET and LeakSeeker will re-calibrate itself again, as soon as the PROBE is
touched to the correct pad. Remember that all tests must start by pushing the RESET
button to clear the memory.
During the normal test, you would touch any pad along the “shorted” foil and allow
LeakSeeker to recalibrate automatically as you get closer to the defect. However, if all
of the solder pads seem to have the same tone because of the low resistance of the
ground plane power source of a multi-layer board, using a higher GAIN allows you to
increase the resolution many times.
NORMAL TESTING
You should be sure that you are looking for a shorted or leaky part by verifying that the
pc board trace you are about to test shows a suspiciously low ohms reading. A quick
method for checking any type of unit for shorts is to simply measure the resistance
across the largest main filters in the power supply with your ohmmeter. In a normal
circuit, you will usually see the cap charging up to several thousand ohms. Any cap that
shows 50 ohms or less is probably the supply line that feeds the shorted component. Be
advised that using an ordinary DVM ohmmeter will not find active shorts. Instead, use
the LeakSeeker as you would an ohmmeter. Normal circuit conditions would produce no
warnings, while passive or active shorts 300 ohms or less will make LeakSeeker
calibrate to the short and give you a steady reading.
For example, a normal power supply output usually shows several thousand ohms, after
the filter caps finish charging. If you feel that you have a problem with the supply
because voltage readings are low while the unit is powered up, remove power and use
an ohmmeter across the cap to see if the reading is lower than 300 ohms (the maximum
range of the LeakSeeker) to ground. Typically, most good supplies show resistances in
the thousands of ohms while most with "shorts" will show just a few ohms, or even less
than an ohm. The exception to this for instance is when you suspect an active short,
where a supply is pulled down by a component that does not show shorted with your
ohmmeter. This can happen when, for example, a component shorts, but is powered
through a diode. Although your ohmmeter cannot measure past the diode, the
LeakSeeker can. A steady tone after the LeakSeeker calibrates indicates that it found a
suspicious reading under 300 ohms and your search can go on. If it simply chirps or
gives no reading at all, then no short (active or normal) was found.
3

GETTING STARTED
Look at the GAIN switch. Notice that the lower gain setting is best for thin pc foil traces,
and should be your first choice. If you notice very little pitch changes as you hop from
pad to pad, you can raise the GAIN, as the foil traces might be thicker. You would use
the highest GAIN setting for very thick traces or multi-layer boards with ground planes.
In the NORMAL test, the BLACK ground wire alligator clip is connected to the best
ground available, preferably at the power source. The connection must be of high
quality or the results will be misleading. You can ignore the alligator clip and solder the
bare wire (behind the alligator clip) to ground to eliminate this source of errors. Push
the RESET button to let LeakSeeker know to start a new search. The test probe is then
touched on a solder pad anywhere along the pc board copper trace that you believe a
shorted or leaky component is soldered to. If the board is dense, you might use a thin
Sharpie marker to outline the trace, to prevent confusion so that you don't accidentally
touch the wrong pad.
As you hold the test probe on the first pad, LeakSeeker will beep at its highest pitch and
light the WAIT lamp brightly for a few seconds as it ramps quickly down to the short
value. Be patient. As it gets closer, the search will slow, the WAIT LED will flash dimly
and you will hear the pitch clicking step by step as it gets a few milliohms closer and
closer. When it has calibrated, the pitch will be low and steady and one (or a group) of
the nine distance LEDs will be lit. Touching the test probe to the next solder pad along
the pc trace should make the pitch higher or lower, depending on whether you are
moving in the correct direction. The distance lamps will also give rough indications that
you are getting closer or further from the defective component. As you touch the probe
from pad to pad in the correct direction, the beeps will get higher in pitch and the
distance LEDs will go CLOSER >>> to the green LEDs. As you get out of range of the
window, the WAIT LED will come on as LeakSeeker recalibrates the window. If you get
further from the short, the LEDs will reverse toward the red LEDs and the pitch will get
lower. You should always make it a habit to go back one pad after each new pad test to
make sure the pitch is higher on the new pad and lower on the old pad, as LeakSeeker
will recalibrate very quickly and you might not notice.
If you accidentally touch the probe to a wrong pad not on the shorted circuit, like maybe
ground, and LeakSeeker notices the huge change, it intentionally waits a second before
accepting the huge change and recalibrating. The delay is intentional; if you accidentally
touched the wrong pad (like a ground), this delay gives you the time to change your
mind as long as you lift off of the pad before the WAIT LED comes on and recalibration
is complete. You should always double-check your progress by touching the previous
pad--- the pitch should be lower than the pad closest to the short. If you goof, just press
RESET and start off the last valid solder pad.
4

On older boards with large traces, or on multi-layer boards with ground-planes, you may
find that many pads close to each other may have the same pitch. Use the highest
GAIN setting and now you will see and hear a slight change between the two pads. The
pad with the highest pitch is your objective. When the tone no longer changes and the
WAIT LED is off, the window is perfect.
As you touch each pad, remember to always go back one to double-check that the tone
is lower (or gone completely as that window is now long gone). At some point, the beep
will be highest in pitch at only one pad along the trace. This is the short, and may be the
location of the defective component. If you continue past this pad, the pitch will start to
go lower and the distance indicator will start to head towards the red indicators. If you
backtrack, the pitch will always be highest at the pad with the lowest resistance, and of
the possible defective component.
BUT WHAT IF THE HIGHEST PITCH CAN'T BE THE BAD PART?
If the highest pitch comes from a pad that is a jumper or wire, or coil or transformer, for
example, a component that is supposed to conduct, this means that the defect is
probably on the other side of the component, in another area of the board. For example,
if you are tracing a short at the collector of the horizontal output transistor and find that
the highest pitch is at the flyback transformer primary, this does not necessarily mean
that the transformer is shorted; the short may be on the other side of the winding, at the
B+ supply. Follow it like a detective, as you may find that you may be jumper-hopping,
coil-hopping, possibly even board-hopping, for example from the HV board, to the
supply board and so on, to where the bad part actually is. The obvious parts that could
be bad are parts that should never show as a low resistance in the first place, such as a
capacitor, cathode of a diode, B+ pin of an IC chip and so on.
USING THE HOT/COOL THERMAL TEST METHOD
If the defect is several ohms, you can search for the defective component in another,
much easier way. To keep your hand free to hold a can of freeze spray or a soldering
iron or hot air blower, use the extra plug-in test cable supplied with LeakSeeker that has
the solder wire tip, plug it into the REF+ port, and solder the tip to any pad along the
shorted trace. The test mode switch remains in the NORMAL position, which joins the
REF+ and PROBE ports together. Press the RESET button and wait for a stable
reading.
Higher resistance defective components are always thermally responsive. You can use
a can of freeze spray to spray each component on the board while the solder tip test
cable is soldered on the suspected trace. The spray will make the LeakSeeker change
quickly in pitch when the defective component is sprayed.
5

3-WIRE TESTING
3-Wire testing is used for times when Normal testing becomes difficult. In these cases, a
component may not be shorted, but just leaky; perhaps 50 or more ohms, and a
capacitor along the trace tries to charge each time the test probe is touched to a pad.
Instead of steady tones, the LeakSeeker will chirp from high to low, or the pitch will vary,
making testing very difficult in the NORMAL position as you wait forever for the pitch to
get stable, but the 3-Wire test will separate the REF+ from the PROBE port, and allow
the circuit to stabilize under power. Only use the 3-wire test for higher-ohm shorts over
about 10 or 15 ohms and when normal testing is too difficult.
Solder the REF+ wire solder tip to the normal source of the power in the supply line you
are troubleshooting, for example, at the output of the power supply at the big electrolytic
that shows a short to ground. This is important, as the 3-Wire test does not allow testing
to start anywhere on the board as the NORMAL testing allows. Make sure the mode
switch is in the 3-WIRE test mode. You must start probing at the normal source of
power, like at one end of the trace by the large power supply capacitors. Allow about 15
seconds for all voltages, currents and temperatures to stabilize, push the RESET
button, then touch and hold the test PROBE at the starting point where the REF+ is
soldered, and allow LeakSeeker to calibrate. Then touch each pad along the bus and
proceed as you would in the NORMAL test. Each reading should now be quick and
easy since the special signal from LeakSeeker REF+ now is no longer changing.
As you proceed, just as in the NORMAL test, the pitch of the tone and distance
indicators will guide you towards the defect. As you probe different branches, you will
find that some branches do not have any changes from pad to pad. That is because
there are no problems in that branch. Go back to the fork and try another branch.
At some point, you will reach the defect and pass it, and the distance indicators and
tone pitch will again no longer change, just like the previous branches that had no
problems. The first pad on the branch that is highest in pitch is the location of the defect.
Going back towards any other branch will cause the tone to get lower, and going
forward will no
longer cause the highest pitch to change. Therefore, be sure to notice the exact location
at which point the readings no longer change as you pass the defect. The exact location
of the first pad that has the highest pitch will be the exact location of the defect. All pads
beyond this point will have the same pitch as the first pad of the highest pitch. You can
verify the defect by using a blast of freeze spray or directed heat on the suspicious
component. LeakSeeker will change pitch drastically only when the defective part is
cooled or heated.
6

TUTORIAL
To best be familiar with LeakSeeker, try this little experiment. It will give you the
direction and understanding in real time of how to use LeakSeeker. You will intentionally
create a defect by soldering in a low-value resistor across a capacitor in a power supply
trace, and then use your LeakSeeker to find it.
On an old pc board or discarded electronic component, locate a power supply trace on
the main board and check the resistance to ground. You will see how a normal circuit
should show, probably a few thousand ohms. Now, solder in a low-value resistor across
a large capacitor, or maybe somewhere further down the trace to ground, to simulate a
leaky capacitor. For example, you could solder a 4.7 ohm resistor to ground at an
integrated circuit B+ or small filter cap. (Of course, don't power up the unit, or you might
damage its power supply). Use your DVM or ohmmeter to verify that you get the same
4.7 ohm reading to ground, everywhere along the trace.
With the LeakSeeker power switch in the NORMAL test, push RESET once. Start at
some distance from the “short” resistor, along the same foil. Use a Sharpie marker if the
trace is very thin so you don't get lost. You should follow the instructions for the
NORMAL test and follow the LeakSeeker's advice, tracing a path along the PCB foil
trace pads, wires, jumpers and connectors, and end up at the resistor that you soldered
in. (Don't forget to remove the tutorial resistor from your experiment when done!)
As you progress, you will get the feel and the personality of your LeakSeeker. Try the
3-WIRE test method only after you have mastered the NORMAL test, as this test is
more difficult. You'll usually only need this test with shorts higher than 10 ohms anyway,
which are rare.
SELF-TEST OPERATION
The LeakSeeker has some test traces built into the front panel. There are two Mil-Max
sockets that you can plug a low value resistor into to simulate a short. Connect the GND
lead to the GND terminal to complete the GND side. Probing along the various traces
will demonstrate the functionality of the unit and confirm it is working. Be sure to remove
any resistor before actual testing.
IN CASE OF TROUBLE
If you accidentally forget to remove power from the unit under test, the power would try
to feedback into the LeakSeeker and cause damage. There are two 0.47 ohm fusible
resistors R15, R22 and a 1N4734A, DZ1 zener diode soldered to the board near the
test probe, clearly marked on the board. These are designed to self-destruct and protect
the LeakSeeker's electronics. There are indications that these protection devices have
done their job; LeakSeeker will immediately beep and try to calibrate to nothing as soon
as it is turned on and the RESET button is pressed if the zener diode is shorted, or you
would get no function at all if the fusible resistor is open.
7

CONTACT INFORMATION
David Humphreys
[email protected].com
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