A.13. Components and Subsystems

Complicating this whole matter of hardware testing is that systems are often comprised of various components and subsystems. These need to be tested separately before they're integrated into your system, but they also need to be tested in the system. Special tests might be required, depending on the subsystem.

Video cards, modems, networking cards, USB controllers, and other I/O components are a prime example of this. Signal quality testing of the incoming and outgoing signals is important, even on pins that are supposedly not used. I once worked on a project where the vendor had assumed that that words not used associated with a particular pin in the requirements specification for the connection to a monitor meant they could use that pin to adjust the monitor's image size on the assembly line. The vendor learned during testing that the words should have been not to be used, because an internal video chip controller signal was present on that pin, causing sporadic resizing of the image!

Thermal testing can also be a concern. On the IVR project I've referred to in this book, the telephony cards included high-speed processors. These cards were packed together in a VME bus in the system rack with four fans to move air over the cards. During thermal testing, I had the testers instrument these chips so that I could check for overtemp conditions during high heat portions of the test cycle.

Systems often include screens—ranging from simple LCDs to advanced ...

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