Page 48 - Building A Succesful Board-Test Strategy

34 BUILDING A SUCCESSFUL BOARD-TEST STRATEGY

longer than in the factory, and identifying the actual cause of a subtle failure may
be difficult or impossible.
If, as with governments and military contracts, customers demand unusual
conditions such as particular test equipment in the field, there is no alternative but
to comply. These constraints simply become part of any test-strategy specification.
If, on the other hand, the requirements are part of a request and are subject
to negotiation, the system manufacturer should try to ascertain the reasons for
them and try to address those concerns in a more appropriate way. One alterna-
tive to test equipment in the field might involve keeping full sets of spares on-site,
isolating a problem to the offending board or assembly module, swapping it for a
good one, and sending the faulty copy back to the factory or to a central depot
for repair. In the case of the locomotive-electronics manufacturer, within 6 months
of first delivery, the customer realized the additional headaches that the require-
ment for extra test equipment had caused, and abandoned the idea in favor of addi-
tional spares.
One large-system manufacturer's customers demanded a product that they
could repair themselves to the component level. The manufacturer, therefore,
included a lot of built-in diagnostics and troubleshooting techniques. After a
few months, however, those same customers decided that the ordeal of stocking
extra components and performing tests was too great, so they reverted to board
swapping and sending defectives back to the vendor.
Bundling a comprehensive spares kit with system sale is generally far more
cost-effective than supplying a tester. Unfortunately, backing away from a strategy
that is already in place is sometimes difficult because of all the money and
political and emotional energy that went into the original decision. Therefore,
companies often stay with a strategy long after it becomes clear that it is not
the best alternative.
A different set of concerns arises when the product is a PC, television set, or
other relatively expensive piece of consumer equipment that an independent
general-purpose service facility will repair. These repair technicians see a wide
variety of failures every day, but they rarely have a great deal of expertise on any
particular brand or model. Manufacturers of this type of product should pay
careful attention to self-tests, service manuals, availability of test nodes for probing,
and other conveniences to facilitate fault isolation and repair. Some of these
solutions will affect test strategies in the factory, whereas others will relate only
to customer-initiated service.

1.6.5 Other Considerations

The question of who performs testing depends heavily on where actual pro-
duction occurs. Some system manufacturers test their own boards; others farm
some or all of the task out to a third party. Manufacturers who produce boards
in-house will likely test them as well. Contract manufacturers may or may not test
the boards that they build or may perform only some of the necessary tests.
Customers may prefer to maintain control over quality by performing all testing