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Diagnostics
Scenario: Several devices never work, but others are ne
Possible causes: Controller/hub compatibility, congurations for USB controllers, power management, con-
troller drivers, device drivers, bandwidth
Should you experience this issue, move the working devices to another root hub to see if the problem is in a
particular root hub or with the devices themselves. If an Ultra camera is moved to a hub that has not loaded
the device drivers the Operating system will prompt the user to load these drivers. This procedure is auto-
matic. Remove external hubs from the equation to see if they are the problem. Try the problematic devices
individually on the computer; if they work, it’s either a device driver or power issue. If they never work, it’s
a controller compatibility issue, a device driver problem, or a lack of bandwidth. Solving compatibility issues
and driver errors requires updating drivers or obtaining appropriate patches.
Scenario: Several devices occasionally stop working at the same time, while others are ne
Possible causes: Power management, device drivers, bandwidth
As you would with any other sporadic hardware conict, try to isolate the particular event that’s common to
all failures. The system may be experiencing a sporadic controller failure if your devices are split across root
hubs. Try moving the devices to another root hub to see if the problem is in a particular root hub or in the
devices themselves. Remove external hubs from the equation to see if they are the problem. Try the prob-
lematic devices individually on the computer; if they work it’s a device driver, power issue, or bandwidth pinch.
Power management
Most computers have some form of sleep mode connected with the screensaver. A controller is not harmed
when an energy setting kicks and eliminates its power. However, the OS may fail to power up the controller
again. You can eliminate this error by opening Power Options and disabling System Standby,
Excessive loads on the bus can also cause power problems. The USB controller can power USB devices.
Small devices like mice and keyboards aren’t a signicant drain, but larger devices—such as scanners, hard
drives, Web cams, and speakers—can draw considerable power. You might be able to eliminate the problem
by spreading the power-hungry devices across multiple root hubs. Otherwise, acquire a good self-powered
external USB hub.
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