PC Hardware

Troubleshooting Modems

It can be very frustrating when a modem does not function as expected. However, follow these simple guidelines to determine whether the modem is really broken or something else is the culprit.

New hardware was added to the computer and now the modem doesn't work.

Check for IRQ and/or I/O conflicts.

New software was added to the computer and now the modem doesn't work.

Check for IRQ and/or I/O conflicts. Cards that were configured for software can be inadvertently changed by corrupted software or by the installation of new software.

The software says there is no modem.

Make sure the software is looking at the correct port. Reconfigure or reinstall the software (there might be a corrupt driver).

Modem works sporadically.

Try another modem type.
Check the phone lines.

Modem does not hang up the phone line.

A power surge (lightning) can cause this problem. If manual disconnect and reconnect allows the modem to work, replace or repair the modem.

Lesson Summary

The following points summarize the main elements of this lesson:

  • Modems convert parallel digital data to and from serial analog data.

  • Modem speeds are based on bps (bits per second).

  • CCITT (now ITU-T) establishes standards for modem communication.

  • AT commands are used to manually communicate with and test a modem.

  • Modems can be installed internally or externally.

  • The primary modem problem is IRQ conflicts.

Lesson 3: Cables and Connectors

Cables and connectors are critical to the operation of any computer peripherals. A computer professional must be able to identify and understand the various types of cables and connectors. This lesson discusses common connectors and their functions.

After this lesson, you will be able to:
  • Identify cables and connectors by their names and functions.
Estimated lesson time: 20 minutes

Parallel printer ports and cables are used to connect printers and other add-on items such as CD-ROMs, tape drives, and scanners. Centronics Corporation invented the most common type. It is an 8-bit parallel connection with handshaking signals between the printer and the computer-these tell the computer when to start or stop sending data. A standard printer cable is configured with a 36-pin Centronics connector on the printer end and a standard 25-pin "D" (male) on the computer end. A standard 25-pin "D" (female) connector found on the back of the computer designates it as a parallel port.