Raspberry Pi A, User Manual, Page: 80 / 314

P A R T I
C O N N E C T I N G T H E B O A R D
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SOMETIMES, THINGS DON’T go entirely smoothly. The more complex the device, the
more complex the problems that can occur—and the Pi is an extremely complex device
indeed.
Thankfully, many of the most common problems are straightforward to diagnose and fix. In
this chapter, we’ll look at some of the most common reasons for the Pi to misbehave and
how to fix them.
Keyboard and Mouse Diagnostics
Perhaps the most common problem that users experience with the Raspberry Pi is when the
keyboard repeats certain characters. For example, if the command
startx
appears onscreen
as
sttttttttttartxxxxxxxxxxxx
, it will, understandably, fail to work when the Enter
key is pressed.
There are typically two reasons why a USB keyboard fails to operate correctly when con-
nected to the Raspberry Pi: it’s drawing too much power, or its internal chipset is conflicting
with the USB circuitry on the Pi.
Check the documentation for your keyboard, or the label on its underside, to see if it has a
power rating given in
milliamps (mA) . This is how much power the keyboard attempts to draw
from the USB port when it’s in use.
The Pi’s USB ports have a component called a polyfuse connected to them, which protects the
Pi in the event that a device attempts to draw too much power. When this polyfuse is tripped,
it causes the USB port to shut off, at around 150 mA. If your keyboard draws anywhere
around that much power, it may operate strangely—or not at all. This can be a problem for
keyboards that have built-in LED lighting, which require far more power to operate than a
standard keyboard.
If you find that your USB keyboard may be drawing too much power, try connecting it to a
powered USB hub instead of directly to the Pi. This will allow the keyboard to draw its power
from the hub’s power supply unit, instead of from the Pi itself. Alternatively, swap the key-
board out for a model with lower power demands. The repeating-letter problem may also be
traced to an inadequate power supply for the Pi itself, which is addressed in the next section,
“Power Diagnostics”.