6 _ _ _ _ _ _ _ _ _ _ _ S~~TECH
Microprocessor Troubleshooting (Part 1)
Troubleshooting is both an art and a science. Once a thorough
understanding of the operation of the circuits and equipment
needing repair is obtained and the basic principles of trouble-
shooting are mastered, practice and experience should result
in an efficient troubleshooter. A proper troubleshooting
process is very logical and begins with an analysis of the
equipment to determine the exact nature of a malfunction.
This is followed by a series of dynamic tests which pinpoint
the fault to a particular circuit, module, or section of the
equipment. Following this, static tests involving the
measurement of voltages, waveforms, resistance, and
current may be made, utilizing manufacturer's literature to
pinpoint the faulty component or components. The necessary
replacements and/or adjustments are made and the equip-
ment is returned to service.
The introduction of integrated circuits and the widespread
use of digital technology has complicated the troubleshooting
process. Recent developments in LSI technology and, in
particular, the microprocessor, have further complicated
troublshooting. On a single circuit board, a technician may
now find a complete computer, including central processing
unit, memory, and interface circuitry. No longer do simple
voltage and resistance measurements enable you to pinpoint
the source of trouble. Even an oscilloscope and digital meter
are inadequate when a technician must examine data with
clock rates in excess of 1 O MHz.
To cope with the complexity of digital systems, a wide variety
of tools and techniques have been developed to aid tech-
nicians in the troubleshooting process. This three-part series
deals with the tools and associated troubleshooting techniques
needed for dealing with complex microprocessor-based
systems. The tools and techniques for troubleshooting in-
dividual digital circuits will be examined.
It cannot be overemphasized, though, that a technician's
most important troubleshooting tool is a thorough understand-
ing of system operation.
Efficient troubleshooting demands proper documentation.
Technicians can no longer afford to spend the time necessary
to analyze each section of a circuit to determine how it shoud
function. This material must be provided by the circuit
designers and made available for the troubleshooting process.
Because of the newness of the microcomputer industry and
the development of suitable microprocessor system trouble-
shooting techniques, a technician may not be able to obtain
adequate documentation. Then, just as when troubleshooting
any other piece of equipment, his best aid is another unit that
is functioning properly. Comparisons are one of the best ways
of localizing faults. Substitutions of individual components
and circuit boards that are known to be good also can be of
considerable aid in the troubleshooting process.
LOGIC PROBES
Although a digital circuit may be quite complex, the very
nature of digital circuitry helps to simplify troubleshooting.