UPGRADING REPAIRING PCs

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Chapter 6—Serial Ports and Modems
Table 6.13 Modem Troubleshooting (All Types) Continued
Modem Type Problem Solution
Any Couldn’t Open Port Modem might be in use already, or IRQ
error message. I/O port–address conflict. Use Device
Manager to check settings, and reinstall
drivers.
System can’t dial Never use a wall jack unless it is clearly
from wall jack. marked as a “data jack” or you check
with the staff. A digital phone system’s
jack looks identical to the safe analog
jack your modem is made for, but its
higher voltage will fry your phone. You
can get phone-line voltage testers from
sources such as http://
warrior.com. If your hotel telephone
has a data jack built-in, use it. Some
hotels now offer built-in Ethernet in
some rooms, so carry your NIC with
you as well for faster Web access.
Internal System locks up Modem trying to share a non-sharable
when trying to IRQ with another port, probably a
boot up or dial mouse. Move a serial mouse that uses
modem. the same IRQ as the modem to a different
COM port with a different IRQ
(from COM 1/IRQ 4 to COM 2/IRQ 3),
or use a PS/2 mouse (IRQ 12). If your
Pentium-class system lacks a visible
PS/2 port, check with your system vendor
for the (optional) header cable you
need.
Disable your system’s COM 2; set the
modem to COM 2 using IRQ 3.
External Computer can’t Check cable type.
detect modem. Must be RS-232 modem (not null
modem or straight-through) cable (see
the following pinouts).
Check power switch and supply.
COM port might not be working.
Check BIOS and enable COM port; test
port with CheckIt, Windows
9x/2000/ME Modem diagnostics, others;
use loopback plug with CheckIt,
AMIDiag, Norton, and so on for most
thorough check.
USB Computer can’t
Check for IRQ conflicts.
Check USB ports; enable if necessary.
detect modem. Check USB cables and hubs.