Troubleshooting Modem Problems Under Windows NT 4.0

The information in this article applies to:

  • Microsoft Windows NT Workstation version 4.0
  • Microsoft Windows NT Server version 4.0


This article describes procedures to help you diagnose and fix problems when you are unable to dial out using your modem in Windows NT 4.0 with Dial-Up Networking (DUN).



Installing Your Modem

If your modem is not on the Windows NT 4.0 Hardware Compatibility List (HCL) or is not detected by Windows NT, use one of the following procedures to install it:

  • Obtain from the modem manufacturer an .inf file designed for Windows NT 4.0. Follow the manufacturer's instructions for installing the modem in Windows NT 4.0. Contact the modem manufacturer for assistance with this procedure.

  • If your modem has an .inf file for Windows 95, you may be able to use that file under Windows NT. When you are adding the modem through Control Panel, Modems, check the box labeled, "Don't detect my modem; I will select it from a list." Choose the "Have Disk" option and insert the disk containing the Windows 95 .inf file. Please be aware that not all Windows 95 .inf files will work correctly in Windows NT 4.0.

  • Install your modem as a standard modem using the following steps:

    1. In Control Panel, double-click Modems. The Install New Modem Wizard starts automatically if you have not installed a modem before. If the wizard does not start automatically, you have installed a modem previously and you should click Add to start the wizard.

    2. Check the box labeled "Don't detect my modem; I will select it from a list," and then click Next.

    3. In the Manufacturers box, click Standard Modem Types. In the Models box, click a model that corresponds to the speed of your modem, and then follow the instructions in the Install New Modem Wizard.

Verify Your COM Port(s)

Verify that Windows NT recognizes your COM port(s) by double-clicking the Ports icon in Control Panel to see if the COM port that the modem is connected to is listed. If it is, Windows NT recognizes the COM port.

If the COM port is not recognized in the Control Panel Ports applet, there is most likely a hardware problem or a configuration problem. Use the following steps to troubleshoot the problem.

External Modems

  1. If the COM port is on the motherboard or is provided by a serial card, make sure the port is not disabled in the BIOS (also called the CMOS) setup of the computer. Refer to the documentation for your computer to obtain information about configuring options in the BIOS setup.

  2. Make sure there are no other adapters or devices that are configured for the same Base I/O Address or IRQ as the COM port to which the modem is attached.

  3. Verify that the serial port is not defective. If the modem and any other serial devices fail on the COM port but work on other COM ports, and you have verified the two steps above, the serial port may be defective.

  4. Verify the serial cable is not defective by using a new standard serial cable.

Internal Modems

  1. If the COM port is defined by an internal modem, make sure the jumpers on the modem are configured properly. Internal modems will almost always have a jumper on the adapter that configures the modem as a particular COM port. There may or may not be jumpers that allow you to set the Base I/O Address and IRQ to be used by the modem as well.

  2. If the modem is configured for a COM port number that is assigned to a COM port on the motherboard or a serial card (physical port), you must either set the modem to use a different COM port, or use the BIOS setup to disable the COM port with the same number as the internal modem. For example, if both the internal modem and the physical COM port are set to COM1, you must either set the internal modem to a different, unused COM port, or the physical COM1 port must be disabled in the BIOS setup.

  3. Make sure there are no other adapters or devices that are configured for the same Base I/O Address or IRQ as the internal modem. Usually COM3, using an IRQ (or interrupt) of 5, is a good choice for an internal modem. However, if you have a sound card, you may need to choose a different IRQ than 5 since many sound cards use that interrupt.

  4. In the Ports component of Control Panel, verify that the IRQ settings and the I/O addresses are correct. Check the System log with the Event Viewer for I/O or IRQ conflict errors.

    When possible, use standard settings for COM ports, which are as follows:
            1 COM1: I/O Address = 3F8h IRQ = 4 SERIAL 2 COM2: I/O Address
            = 2F8h IRQ = 3 SERIAL 3 COM3: I/O Address = 3E8h, IRQ = 4 SERIAL
            4 COM4: I/O Address = 2E8h, IRQ = 3 

  5. You do NOT need to add a new port in the Control Panel Ports applet to add support for an internal modem. NTDETECT will detect the internal modem and the COM port it is configured to use. If a duplicate port was added using the Add button in the Control Panel Ports applet, use the Delete button to remove the duplicate port.

  6. Verify that the internal modem is not defective. Also, it is often a good idea to check with the vendor of your modem to see if there is a flash upgrade available for your modem.

Troubleshoot with HyperTerminal

Verify that Windows NT recognizes your modem and that you can dial out using the HyperTerminal program. To do so, follow these steps:

NOTE: Before attempting to use HyperTerminal, verify that the Remote Access Server service is not running. Double-click the Services icon in Control Panel and verify that the Status column next to Remote Access Server is blank. If it displays "Started," click the Stop button to disable the Remote Access Server service before continuing.

  1. Click Start, point to Programs, point to Accessories, point to HyperTerminal, and then click HyperTerminal.

  2. When the New Connection Wizard is displayed, click Cancel.

  3. On the File menu, click Properties, and then click the modem you want to test to select it in the Connect Using list.

  4. Click Configure, verify that your modem is set to use the correct port, and then click OK.

  5. Type "AT" (without quotation marks) in the HyperTerminal window, and then press ENTER.

  6. If "AT" (without quotation marks) is displayed in the HyperTerminal window as you type it and "OK" (without quotation marks) is displayed after you press ENTER, HyperTerminal recognizes the modem properly. If "AT" is not displayed as you type it or if "OK" is not displayed after you press ENTER, review the previous steps in this article to verify that your modem is installed properly in Windows NT.

  7. Verify that your modem can dial out using HyperTerminal. On the File menu, click New Connection, and then follow the instructions on your screen.

  8. Click Dial. If the modem's speaker is enabled, you should hear a dial tone and the sound of the modem dialing the phone number.

For additional information, please see the following article(s) in the Microsoft Knowledge Base:

TITLE : Troubleshooting PCMCIA Modems in Windows NT 3.51

TITLE : Disabling Remote Access Support for Unimodem Modems

Additional query words: connecting ras dialin tshoot

Keywords : kbhw ntras NTSrvWkst
Version : winnt:4.0
Platform : winnt
Issue type :