When you troubleshoot issues with a serial or parallel hybrid device, there are some quick tests that you can complete to rule out potential problems. You can test to make sure that the following components are working correctly and are not the source of the issue:
Serial or parallel cables
Serial or parallel ports
Serial or parallel devices
To test your setup components, try the following:
Use the serial or parallel cable, serial or parallel port, and serial or parallel device in another setup to see if the problem is with the components or the setup.
Use a different serial or parallel cable, serial or parallel port, and serial or parallel device in your setup to see if the problem persists. Ideally, you should test a component that you know works in another setup.
When you test your cables, it is recommended that you do the following:
Test each cable individually.
Use short cables when you are testing.
When you test the serial or parallel ports and serial or parallel device, it is recommended that you do the following:
Press the Windows key + R, type devmgmt.msc, and press Enter to open Device Manager. Check to see if your device is listed under Ports (COM & LPT).
Make sure that the COM or LPT port number is the correct number for the serial or parallel device and that the software being used to connect the computer to the serial or parallel device uses the correct COM or LPT port number.
If you do not see the COM or LPT port number in Device Manager see this FAQ for PCI/PCIe expansion cards: https://www.startech.com/support/faqs/technical-support?topic=expansion-cards#pci-pcie-cannot-boot-os-or-detect-windows
or this FAQ for USB devices: https://www.startech.com/support/faqs/technical-support?topic=expansion-cards#usb-cannot-detect-windows
If the device is listed with an error, follow the instructions on the website to reinstall the drivers.
Note: Some serial devices work only if the COM or LPT port number is between a certain range. For example, COM1 to COM4 for serial and LPT1 and LPT2 for parallel.
Perform a serial loopback test. See this FAQ on how to perform a RS-232 serial loopback test: http://www.startech.com/faq/serial_loopback_test_rs232_windows
Note: There is not an equivalent loopback test that can be performed for parallel devices.