Ever had a perfectly good HDMI cable just stop working, giving you a blank screen just moments after displaying a good picture? We've seen it multiple times in our years of HDMI cable testing, and there is very little information about it online, with most guides pointing to a 'bad' cable, a damaged HDMI socket or something else that's easy to test for and solve.
This guide is for those other times - when the hardware is perfectly fine, but your display refuses to accept a good HDMI signal for seemingly no reason - usually after a change in resolution or refresh rate.
Sometimes, it seems like the HDMI handshake routine has a mind of its own. If it receives one bad input signal, it can blacklist that source device and refuse to display an image, even after the bad signal comes good. Like it remembers it didn't work that one time, so it won't even try again. This might be a HDCP failure. This might be EDID related. It might happen when you're on the ragged edge of your cable's bandwidth limit, or something else entirely - we don't know why it happens, but it happens.
In our experience, this issue is most likely going to present itself when you are trying to get a specific high resolution signal out of a device. For us, it has been most commonly observed coming from a computer or laptop in excess of 1080p, but it can happen with a games console and sometimes even DVD or Blu-ray players. Basically, if a device has the ability for the user to choose an output resolution, it can run afoul of this phenomenon.
For example, we connected a new HDMI cable between our test bench PC and its monitor. The HDMI handshake and EDID process gave us a nice 4K 144Hz 12-bit image automatically, and everything looked great. As part of our testing procedure, we drop to 4K 60Hz 8-bit as a baseline. That worked fine. Then, we bumped it back up to 4K 120Hz 10-Bit for the HDR test and... Black screen. No image. We know the monitor can do 120Hz HDR on other cables, so it's not an out-of-range issue.
If you're familiar with computers, you'll know that Windows asks if the resolution is working, and if you don't hit OK within 15 seconds it goes back to the last working setup. Well, that didn't give us our image back. Removing and reinserting the cable didn't solve it either. Now, we're stuck with no image and no way to interact with the PC on a cable we know was working fine just moments ago, and at a lower bandwidth video signal than it started with.
We were able to observe the same cable doing the exact same thing with the same test on the same hardware in the same way - twice (after we got the 144Hz image back of course.) It worked fine with other displays, too.
Below is a list of what we try when we have to solve the problem:
Using another HDMI input socket on the display fixed this issue on an LG OLED55C7T when it spat the dummy at 1440@120Hz and wouldn't go back to the previously working 60Hz image. In this instance, the HDMI cable was installed in the wall and ceiling cavity, so it couldn't be easily replaced for testing purposes. This solution is not good if you don't have any alternative HDMI inputs or don't have the authority to change the hardware configuration.
And 1440p at 120 wasn't an issue for the TV at first. It was happy until the image was duplicated from the primary display (extended desktop was working). Changing to one of the other HDMI sockets on the TV gave us 1440p at 60Hz again without issue.
Changing to another HDMI cable has the best results when using a shorter length than before. Longer cables can also work, as it seems any significantly different cable can solve the problem. This solution isn't always practical if you don't have other HDMI cables on hand, but the benefit is you might be able to go back to the previously non-working cable after enough time and testing on the alternate. It worked on the Cable Chick test bench twice in one sitting, but we have more than a few HDMI cables lying around!
This seems to suggest that the memory effect is less to do with the source and more to do with a specific configuration on a specific cable. And it's not simply an out-of-range or bandwidth issue, as the hardware and cable can work reliably in other configurations.
Power cycling in this case means turning off all the connected hardware including source and display, AND unplugging them from mains power for 30 seconds before starting over. This time away from electricity gives the capacitors and circuits inside a chance to drain and 'forget' what they were doing. Plug everything back in and begin again. This solution doesn't always work, and isn't always available if the hardware is in-use or inaccessible. You can also try longer disconnection periods, but anything over 60 seconds is usually unnecessary.
Connect other HDMI sources to the misbehaving HDMI socket. The theory here is to make the TV 'forget' the rejected input signal by giving it a bunch of new good ones. If you have a Blu-ray player, PVR, streaming box, games console or anything else to hand, try swapping devices around for a while before going back to your desired configuration.
If you have another output available, try it. We haven't see this issue with DisplayPort or USB-C Alt-mode. Maybe even a DisplayPort to HDMI adapter is enough to side-step the memory effect?
The final thing to try is to sleep on it and see if things improve on their own. Giving up for the day and trying again tomorrow might be just what the doctor ordered. Your display can't hold a grudge forever, right? Right?
Thank you for reading our strangest article yet. We know first-hand how frustrating it is to have a HDMI connection gaslight you in this way, and we wish you all the best in finding a solution. You're not crazy - HDMI somtimes does strange things!
If you know more about this phenomenon, why it happens or how to solve it, we'd love to hear from you! Contact us and share your story and solutions.