Quick Fixes for Modems

Updated: August 31, 2007

Applies To: Windows Server 2008

This topic provides a summary of the most common modem problems in the Microsoft® Windows Vista® and Windows Server® 2008 operating systems and the solutions to those problems. You can use the information in this topic to resolve problems in the same way that you use a frequently asked questions (FAQ) topic to find answers to common questions. Read this topic before you begin any advanced troubleshooting.

The following are common modem problems and quick fixes:

The modem does not work

The modem always connects at a lower bits-per-second (bps) rate than specified

The modem diagnostics indicate that an external serial modem is not receiving commands

The modem cable is good, but the modem still does not receive commands

The modem is installed correctly but the diagnostics indicate that it is not responding correctly

According to the modem diagnostics, the modem works but you still cannot make a connection

You cannot connect or are having problems connecting to another computer or an online service provider

Your PCMCIA modem card was not detected automatically when you inserted it

An RS-232 serial device is functioning poorly or not at all

A connection in Network Connections reports that a port is in use or not configured for remote access

Cause:  The modem is incompatible with your computer.

Solution:  Check the manufacturing documentation from your modem vendor, or modem vendor Web site, for a modem compatibility overview.

Cause:  The modem is not connected properly or is turned off.

Solution:  Verify that the modem is connected properly to the correct port on your computer. If the modem is external, verify that the power is on.

Cause:  The modem and telephone line are not operating correctly. Excessive static on the telephone line causes sessions to be dropped.

Solution:  Use modem diagnostics to confirm correct modem operation. In Control Panel, click Phone and Modem Options, click the Modems tab, click the Advanced button, and then click the Diagnostics tab. Click the Query Modem button, and then assess the response.

See also:  Log and View Modem Commands

Cause:  The remote access server is not functioning properly.

Solution:  Ask your system administrator to verify that the destination server is running properly. Try connecting to the same server from another computer. If other computers are having the same problem, there might be problems with server applications or hardware. If not, the problem is specific to your computer.

Cause:  The quality of your phone line is insufficient.

Solution:  Contact your telephone company to verify the quality of your phone line.

Cause:  The specific phone line you are dialing is affecting the speed.

Solution:  If you can connect to your remote access server by using more than one number, try another number, and then see if the speed improves.

Cause:  Your modem software needs to be updated.

Solution:  Check with your modem manufacturer for modem software updates.

Cause:  If the modem diagnostics indicate that the modem is not receiving commands, the modem cabling might be faulty.

Solution:  Try connecting the modem with a new cable.

Cause:  The modem is installed incorrectly.

Solution:  Check the modem documentation to make sure that you installed the modem correctly.

Cause:  The incorrect model and make were specified during installation in Windows or an obsolete installation (.inf) file was used to install the modem.

Solution:  Check the modem documentation for the correct model and make or a compatible model and make, and then reinstall the modem. You can check with the manufacturer to see if there are more recent installation files available for installing the modem.

Cause:  The modem is connected incorrectly to the phone line or there is a problem with the phone line.

Solution:  Check the connection to the phone line. If the modem is connected correctly, have a telephone professional check your phone line.

Cause:  The modem is incorrectly configured for the phone line.

Solution:  Check the modem properties, and ensure that they are configured for the phone line in your location. A setting that is commonly configured incorrectly is the Wait for dial-tone setting. For more information, see Changing How Modems Initialize and Connect

Cause:  The data connection parameters (see Changing Modem Data and Hardware Settings) for the two modems are not the same. Data connection parameters for two modems need to be identical for them to connect successfully.

Solution:  Check the hardware transmission settings for both computers. Typical settings, commonly used by Internet service providers (ISPs) and bulletin boards, are:

  • Data bits: 8

  • Parity: None

  • Stop bit: 1

If these do not work, try seven data bits, even parity, and one stop bit. A few ISPs use these settings. Other settings are extremely rare.

Cause:  The built-in COM port on the PCMCIA modem card is not configured.

Solution:  Use Add or Remove Hardware in Control Panel to configure the built-in COM port on the PCMCIA modem card. You can then install the PCMCIA modem by using the Phone and Modem Options in Control Panel. See Install a modem.

Cause:  Some RS-232 serial devices now support speeds faster than the 115.2 Kbps supported by the standard serial ports installed on most computers.

Solution:  If the Port speed in the connection preferences is faster than 115.2 Kbps, then try reducing the speed to 115.2 Kbps. You can leave the Maximum Port Speed in the modem properties at the higher setting. If the serial port on your computer supports speeds faster than 115.2 Kbps, then set the Port speed to whichever is slower, the serial port speed or the device speed.

Cause:  There are several possible causes:

  • When you started Windows, a Plug and Play modem was not connected or it was turned off, so it was not detected correctly.

  • The port is in use by another program.

  • The connection might not have been updated to reflect changes in communications equipment, such as new serial ports or modems.

Solution:  Use one of the following solutions:

  • If the modem was disconnected or turned off, reconnect or turn on your modem, and then either restart Windows or use Device Manager to scan for new hardware.

  • If the COM port is already in use by another connection, hang up the connection, or modify the connection to use a different port.

  • If you have changed your hardware (such as a new serial port or modem), you must reconfigure the connection.

For modem diagnostics, see Test a Modem. Refer to the modem documentation or customer service representative for the correct modem commands and responses.

Make sure to note changes to modem settings and switches as you make them. This enables you to return the modem to its previous state, if necessary.

If you have modem problems, you might want to report them to the modem manufacturer or your supplier. In your report, include your modem log, which records information about your attempts to connect to other systems. For information about creating a modem log, see Log and View Modem Commands.

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