Signal
probing requires some understanding on the circuitry to determine the signal
test point and to interpret the result. Signal probing can be done with a voltage
test using a handheld multimeter or a waveform capture with an oscilloscope. Most
voltage tests start by probing the voltage with reference to the ground. When
checking an integrated circuit (IC), it normally starts with testing the voltage supply pin. If the
voltage level is lower than expected, there could be leakage on the IC.
Sometimes,
instead of depending on a measurement value displayed on the handheld
multimeter, the engineers or technicians will need more information of the
signal by monitoring the waveform pattern to determine the possible cause of
failure. Oscilloscopes will be useful in this situation. The oscilloscope is
used to monitor and display the signal in a graphical format. The oscilloscope
shows how the signal changes, allowing the engineers and technicians to detect any
anomalies easily.
Occasionally,
engineers or technicians will need to make floating measurement in which the
measurement point is not referenced to the earth ground. Most benchtop
oscilloscope measurements are referenced to the earth ground as the signal
ground terminal is connected to the protective earth ground system. The
Keysight U1610A/U1620A handheld oscilloscope offers channel-to-channel
isolation to enable the capture of two signals at different reference points.
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Figure
5 Two different floating measurement waveforms captured using Keysight U1620A
handheld oscilloscope with channel-to-channel isolation (left) and Keysight
U1604A handheld oscilloscope without channel-to-channel isolation (right)
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The
Keysight U1610A 100 MHz handheld oscilloscope and U1620A 200 MHz handheld
oscilloscope with VGA display allow us to clearly see and differentiate signals
from both channels simultaneously similar to working on a benchtop
oscilloscope. The scope isolation channels enable floating measurement
capability. With up to 2 GSa/s sampling rate and 2 Mpts memory depth, the
U1610A/U1620A captures more waveforms from signals and the zoom-in function
allows for a more detailed view.
Comparing the circuit boards
To
determine the root cause of a defective circuit board quickly, technicians will
usually compare the test value of a defective circuit board with a known good circuit
board. This is done by probing the circuit board’s reference points with a
digital multimeter and comparing the values between the defective circuit board
and a known good circuit board.
The
Keysight U1200 series handheld digital multimeters with up to 4 ½ digit display
resolution deliver the precision, accuracy and repeatability that the technician
needs during troubleshooting. Coupled with the U1163A SMT grabbers and the
U1164A fine tip test probes, physically small connections to the device under
test (DUT) such as the SMT component can be achieved.
Intermittent failure
Intermittent
failure is the most challenging part to address in the troubleshooting process.
It can be very time consuming. There are many factors which result in intermittent
failures. The common faults are component overheat, poor soldering and
components degradation. Intermittent failure can be attended by monitoring the
voltage value of the suspected component with a handheld multimeter or an oscilloscope
over time to determine if there are any changes to the signal.
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Figure 6 Monitoring the voltage value over time with the
data logging capability using the Keysight Handheld Meter Logger Software
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