Hardware Reference
In-Depth Information
Electrical Testing Equipment
I consider a voltmeter to be required gear for proper system testing. A multimeter can serve many
purposes, including checking for voltage signals at various points in a system, testing the output of the
power supply, and checking for continuity in a circuit or cable. An outlet tester is an invaluable
accessory that can check the electrical outlet for proper wiring. This capability is useful if you
believe the problem lies outside the computer system.
Loopback Connectors (Wrap Plugs)
For diagnosing serial- and parallel-port problems, as well as problems with network cabling, you
need loopback connectors (also called
wrap plugs
), which are used to circulate, or wrap, signals
(see
Figure 20.5
)
. The plugs enable ports to send and receive data simultaneously for diagnostic
purposes.
Figure 20.5. Serial and parallel port wrap plugs.
To accommodate all the serial/parallel ports you might encounter, you need a loopback connector for
the 25-pin serial port, one for the 9-pin serial port, and one for the 25-pin parallel port. Some
diagnostic software products include loopback connectors with the product, or you can purchase them
as an option. Note that there are some variations on how loopback connectors can be made, and not
all versions work properly with all diagnostics software. You should therefore use the loopback
connectors recommended by the diagnostics software you will be using.
Ethernet loopback connectors are very useful for quickly diagnosing network cable runs, as well as
for identifying which network jacks or cable ends are connected to which ports on a router or switch.
With a loopback connector attached to a functioning cable, the corresponding port on a router or
switch will show a device connected. For example, say you have an 8-port switch with cables
connected to each port, but you don't know exactly which remote jacks in the home or office network
they are connected to. Merely attach the Ethernet loopback to a jack or cable end you want to
diagnose, then look at the switch to see which port lights up, thereby identifying the port in question.
USB wrap plugs are also available. However, these are active bus-powered devices that require
compatible drivers and software from the plug manufacturer.
Note
Serial, parallel, and USB loopback plugs and testing software are available from PassMark
Software (
www.passmark.com
)
, and Ethernet loopback connectors are available from
Smartronix (
www.smartronixstore.com
)
.
Meters
Some troubleshooting procedures require that you measure voltage and resistance. You take these
