First off, I know almost nothing about the way a modern TV works.

I have a 4K TV with 3 HDMI ports. We use one for DVDs, one for TV set-top box, one for CCTV.

We can plug DVD or CCTV into any of the HDMI ports and they display with no problem. OTOH, the set-top box will not display a picture whichever port we connect to. Line from dish > STB is fine, STB is fine, HDMI cable is fine - we've proved this by connecting to another TV set which easily displays a picture.

I accept that the problem appears to be in the TV but here's my main question ......

Is there circuitry within the TV that 'does something' to the STB signal so that a picture is displayed? I'd have thought that the STB does all that but it seems I'm mistaken.

Just trying to learn here. I'll probably buy a new TV, even though it seems a waste for what looks like such a small problem.

Next test should be to connect the STB to a different TV using the HDMI cable you know works.

Just now, gamb00ler said:

Next test should be to connect the STB to a different TV using the HDMI cable you know works.

Thanks for replying but already done that ......... "Line from dish > STB is fine, STB is fine, HDMI cable is fine - we've proved this by connecting to another TV set which easily displays a picture".

Does that TV auto detect, or if using more than one port, do you need to select which source / channel is displayed.

Just now, KhunLA said:

Does that TV auto detect, or if using more than one port, do you need to select which source / channel is displayed.

Doesn't auto-detect. All 3 ports are permanently connected and we switch source as necessary. If I move STB connection from, say, HDMI 1 > 3, then of course the source HDMI is changed to suit. Channel selection is done on STB.

Problem with TV (or box), but don't post name of TV (and box).

So not really worth anyone's time to try and help.

Edited May 1May 1 by BritManToo

Would also help to know what the model of set top box it is

if its a True vision satellite box maybe (total guess) it has some sort of 'DRM' digital rights management that the TV is not compatible with but others are also try other HDMI leads they are not all the same.

The STB generates the picture, but the TV must agree to accept it via the HDMI handshake (EDID + HDCP). If that process fails, you’ll get no image. Without the exact TV and STB models, we can’t pinpoint the incompatibility—only suggest likely causes. In my case it was not using the right HDMI-cable in the proper port. Even if everything “should” be compatible, HDMI setups can be picky—using the right port and a suitable cable can make all the difference.