Input-to-Output Method: This method involves measuring or testing the input to a functional
module. If the measurement is satisfactory, then look at the output of the module.
If the output is satisfactory, then the module under test must be good. Move on to the next
module.
Output-to-Input Method: This method is the same as the approach above, except that
the output is tested first. The choice between the output-to-input method or the input-tooutput
method is a matter of convenience. Use whichever is easier and quicker.
Half-Split Method: This is a good method to use if there are a large number of identical
functional blocks in series or a number of identical circuit cards in an instrument. Test
or measure the output from the middle block or circuit card. If the results are correct, then
the first half of the blocks are OK, and the problem must lie in the second half. Split the
second half of the blocks in half, and measure the signal. If the signal is incorrect, the
problem lies between the half and 3/4 block. Further measurements will isolate the problem
to a particular block or circuit card. The half-split method is very efficient in searching
for a problem in a large number of identical functions that are connected in series.
However, several assumptions are made:
● All circuit blocks are equally reliable.
● Only one fault exists.
● All measurements are similar and take the same amount of time.
Most systems do not consist of only series-connected blocks but possess parallel
branches and feedback loops. The connections that complicate fault location are: