When you troubleshoot issues with a serial 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:
To test your setup components, try the following:
Use the serial cable, serial port, and serial device in another setup to see if the problem is with the components or the setup.
Use a different serial cable, serial port, and serial 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 ports and serial 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 port number is the correct number for the serial device and that the software being used to connect the computer to the serial device uses the correct COM port number.
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 port number is between a certain range. For example, COM1 to COM4.
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