Client has 2 rooms with nearly the exact same setup: Samsung cable box (stupidly, I forget to write down the exact model, but it's the same in both rooms) connected directly to a Samsung UN55LS003 with a passive HDMI cable connected to HDMI input 2.

In one room there are no issues. In the other room, the TV displays "No signal."

The room without the issue has just a 3m HDMI cable. The problem room has a 25' cable. The funny thing is that when connecting a PC to the 25' HDMI cable, we get an image. And, when we connect the cable box in the problem room to another TV, we get an image.

So, superficially, you can say the cable box works, the HDMI cable works and the TV works, but they don't work together - even though the same model cable box works with the same TV in another room.

I suspect the HDMI cable might not be doing a great job carrying the DDC signal, and that the PC was doing a better job overcoming this issue than the cable box.

I am going back next week to try inserting an HDMI splitter between the cable box and TV to see if that helps. It's a long trip for us, though, so I'd much appreciate other thoughts on what to try during the visit.