Ernie,
It sounds like you do not own a single piece of video test equipment. How, how can you honestly work on customer's systems, when you are just as blind as they are trying to troubleshoot things.

At the very least, you can put a test pattern app on your phone or tablet and 'cast' or 'airplay' it to a device (Chromecast or AppleTV).

A step up would be to use a bluray player or 4K bluray player with test discs (there are dozens available) and hook to a display.

Another step up would be to use an actual pattern generator. There are cheap Chinese ones on Amazon.com for $300-$600.

If you really want to go pro, buy an actual professional test pattern generator. I like the Murideo SIX-G at $2500.

Of course you will need to know how to actually use the test patterns as well. And you would need to know what all the controls on the video display actually do. I'm not convinced that you do.