Digital Electronic 1 Laboratory Manual
Troubleshooting Method:
If at any time during the experiment the results do not match the theoretical or expected
results use the logic probe to troubleshoot the circuit. There are many approaches to
troubleshooting and as you gain experience your method may change, but this is a
good basic method to troubleshoot the circuits in this course.
• First, recognize the location of the visual fault. For example, the LED 1 is always
on or the display does not show the correct value. The goal is to determine why
the visual fault exists. The location of the visual fault is the starting point of the
troubleshooting, but the actual root cause of this fault may be located elsewhere
in the circuit.
• Next use the logic probe to check for power (HIGH) and ground (LOW) voltages
at the first chip in the signal chain that is closest to the visual fault. Once all the
power and ground voltages have been verified the focus will be on the individual
signals that feed into this chip.
• Since the troubleshooting method is starting at the visual fault area there should
be an incorrect output signal. Locate the incorrect output signal(s). Use the logic
diagrams, datasheets, schematics and logic probe to trace the incorrect signal
back towards the source of the signal. This may involve verifying other inputs to
the chip are correct.
• If the incorrect signal leads to another chip first verify the power and ground
voltages to the chip and then continue to trace the incorrect signal back to it
source.
• The goal is to locate where the incorrect signal has gone correct. At this point the
focus would be on understand why the correct signal has gone bad at that
location. They are many possible causes of a circuit not functioning properly. It is
important to gain experience and build confidence in troubleshooting.
Developing effective troubleshooting skills are like learning to ice skate. We can read
about how to ice skate till the cows come home, but at some point you need to get on
the ice and try to skate. The actual experience and trial and error is the best way to
learn how to ice skate and troubleshoot electrical circuits.
Again, as you gain experience you may want to consider a troubleshooting method that
utilizes a “divide and conquer” approach. When done properly this method can shorten
the time to locate the fault. Troubleshooting is a skill that enhances value as an
employee.
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