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[ The PC Guide | Troubleshooting and Repair Guide | The Troubleshooting Expert | Troubleshooting Specific Components | Troubleshooting Peripheral I/O Ports ]

I cannot get my printer or other parallel port devices to work properly on my system

Explanation: You are having problems getting your printer to work on the PC. Generally this manifests itself as the printer not being seen by the computer.

Diagnosis: There are several common causes of this problem. First is physical misconfiguration, such as loose or incorrectly connected cables. This is usually seen when the PC is first put together. Problems sometimes result from incorrect printer drivers or incorrect settings. Also, the use of advanced printer port modes can sometimes cause problems.


  • First of all, make sure that you are testing with a printer that you know works. Also, to test basic connectivity, don't do fancy things like printing color graphics from Windows. Try printing a plain text file for starters. Test the printer on another PC to make sure that it is working correctly.
  • Check the BIOS setting that controls the IRQ assigned to the parallel port. Normally, IRQ 7 is assigned to LPT1, the printer port present on most systems. If you have it set to IRQ 5, then you may have a conflict with your sound card, since they usually try to use IRQ 5 for themselves.
  • If you have ECP mode enabled on your parallel port, watch out for resource conflicts and also incompatibilities of various sorts. I have seen devices just not work properly when ECP mode is turned on, because some software and hardware just does not deal with it properly. Disable it at least until you resolve your difficulties. Also, ECP mode usually requires the use of a DMA channel. Sometimes the default DMA channel chosen is DMA 1, which is also the default for many sound cards. Try changing it to 3 if you are going to use ECP.
  • If your printer requires bidirectional communication in order for its driver software to work properly, you will need to make sure the parallel port is set to enable bidirectional mode. This usually means setting the port to bidirectional or EPP mode.
  • If you are using multiple parallel ports (i.e., LPT2 or LPT3 instead of the more common LPT1) then you need to double-check to ensure that they are set to correct resources that will not conflict with other devices.
  • Check the driver that is being used to access the printer. Make sure that it is the correct type and is installed correctly. Try getting an upgraded driver from the manufacturer's web site.
  • Check the external connections to make sure they are not loose. Check the cables running from the port to the motherboard headers to make sure they are tight as well.
  • If you just installed a new system, or especially if you just upgraded your motherboard in an existing system, and you are using an AT or baby AT style motherboard, you should have used the cables that came with the board to connect to the parallel port connector on the back of the system case. These cables are not universal. If you upgrade your motherboard and try to save time by leaving the old cables in place and connecting them to the LPT1 port header on the motherboard, your port may not work.

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