Thank you for reaching out to us on our online Answers Forum. I can understand why you would want to test the cables before attempting to get new ones. I am glad to assist you with this. There is a test you can run call the camera test. The flash from the IR cable can be seen from a digital camera while looking at it. So if you have a phone camera, a digital camera, even a web camera you can do this test.
Here is the article on how to perform the test:
Hopefully that helps out.
The Sling Media Moderation Team.