Diagnosis of Malfunctions in Complex Electronic Assemblies. Final Report. Page: 48 of 66
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The failure of a driving transistor sometimes burned a resistor which de-
laminated a printed circuit board, causing the entire assembly to be scrapped.
When troubleshooting units which are known to have a gross defect and when
full supply conditions need not be applied to display the defect the reduction
of input power can be a beneficial precaution.
Most of the oscillator section of the power supply was contained on one .
printed circuit board. If problems existed in this section, isolation of the
individual components in the final power supply configuration was difficult
because of the inaccessibility of circuit nodes and the frequent necessity of
breaking the electrical circuit. No tester was available to evaluate the
individual printed circuit board assembly. Neither functional evaluations
nor verification after rework was possible if the oscillator printed circuit
board assembly was rejected as a unit.
The circuit nodes that were most often examined to make diagnostic judg-
ments required the connection of probes to component leads which were near
other components and often difficult to get to, creating a condition conducive
to accidental shorting of the circuit node under test to adjacent circuitry
by the probes being used for evaluation.
Tester Development. A set of specifications and preliminary sketches
were developed to define a tester that would be more economical and have
better diagnostic capabilities than an inspection tester. The tester design
criteria are outlined below.
" The tester shall excite and load the oscillator printed circuit board
assembly, the final power supply assembly, and the next-higher assembly.
e The tester shall bring out all accessible test nodes to jacks on the front
panel and identify the nodes by schematic symbols compatible with those
of the troubleshooting manual. The reduction of necessary probe con-
nections reduces the likelihood of accidental short by evaluation probes.
" The tester shall allow any dc load to be removed or applied separately,
but only when the power is removed from the unit. The removal and
application of a load during operations generates undesirable transient
" The tester shall lock out over-voltage and over-current conditions.
" All applied voltage shall. be continuous and adjustable from 0 to a maxi-
mum operating range.
" The tester shall interrupt troubleshooting operation after a specified
operating time at spe.ific current levels by disabling the power to the
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Losure, J. A. Diagnosis of Malfunctions in Complex Electronic Assemblies. Final Report., report, January 1, 1971; Kansas City, Missouri. (https://digital.library.unt.edu/ark:/67531/metadc1031893/m1/48/: accessed March 22, 2019), University of North Texas Libraries, Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.