Wirebook › Bonus lesson
Why does the TV say "No signal"?
Plug a games console into a TV and, for a second or two, nothing happens. Then a picture pops up. In that gap the two of them have had a whole conversation: a handshake. The TV says hello and hands over a menu card of every picture it can show, the console picks the best thing on both lists, and for films they swap a secret password. When the conversation goes wrong, you get the two most annoying words in the house: No signal.
Step 1: "I'm here!"
An HDMI cable has 19 little wires inside. Most carry the picture, but one is just for saying hello: when the TV is switched on, it puts a tiny voltage on the hot plug wire. The console notices and knows a screen has woken up at the other end. That's why switching the TV on first and the console second fixes so many No signal problems: the console hears the hello at the right moment.
Step 2: the menu card
Next the TV hands over a small chip's worth of facts about itself, called the EDID. Think of it as a menu card: its name, every resolution and refresh rate it can show (4K at 60, 1080p at 120 and so on), whether it can do HDR, and what sound it can play. The console reads the menu, compares it with its own list and picks the best dish on both: "Okay, 4K 60 it is!"
Two things can change the menu. Many TVs ship with their enhanced HDMI setting switched off (it has a different name on every brand), so they hand over an old, short menu without 4K 60 or HDR. And anything in the middle, like a soundbar or splitter, rewrites the card and crosses out everything it can't carry itself.
Why can't the console see the cable?
Here's the sneaky part. The menu card comes from the TV, not the cable, so the console has no idea whether the cable can actually carry the mode it picked. 4K at 60 needs about 18 gigabits every second. An old cable that only carries 10 sends it anyway and drops bits on the way: you see white sparkles, the screen blinks black every few seconds, or it gives up with No signal.
The newest, fastest modes, like 4K at 120, learned from this. Before the picture starts they test the wire with a burst on the fastest lanes, and if it coughs they step down to a slower mode that fits. That's why a TV can say "120 Hz" while the console greys the option out: the cable failed the test.
Step 3: the secret password
Films and TV apps don't want anyone recording them on the way to your screen. So before a film plays, the console or streaming stick checks that every box on the path knows a secret password, called HDCP. A TV and a decent soundbar know it. A cheap splitter or an old capture box often doesn't, so the menus and games still show but the film turns black or shows an error.
Why does a new TV give "No signal"?
Usually because someone told the console, by hand, to always send one particular mode. The old TV could show it, the new one can't, and a console that's set by hand doesn't read the menu card any more. Every console has an escape hatch that starts it in a safe, low resolution so you can set the output back to Automatic: on a PS5, hold the power button until the second beep for Safe Mode and choose Change Video Output; on an Xbox, hold power and eject (or power and pair) when starting it.
Soundbars in the middle
A soundbar between the console and the TV has to carry the whole picture just to get the sound out of it, and an older one can't carry 4K or 120 Hz. The neat fix is to plug the console straight into the TV and connect the soundbar to the TV's eARC port. The sound then travels backwards down that cable from the TV to the soundbar, and the picture never goes through the soundbar at all.
When it isn't the handshake
If nothing on the menu, cable or middle box explains it, do the full restart in the right order: both off at the wall for a minute, push the cable in firmly at both ends, TV on first, then the console. Try another HDMI port, and make sure the TV is set to the input you plugged into. A surprising number of No signals are the TV politely showing HDMI 1 while the console is in HDMI 2.
So why does the TV say "No signal"?
Because the picture only starts once the handshake works. The TV says hello, hands over its menu card, the console picks the best mode they share, the cable has to carry it and, for films, everyone in the chain has to know the password. Break any step (a console forced into a mode that isn't on the menu, a cable too thin for what they agreed, a box in the middle that crosses things out or doesn't know the password) and the screen has nothing to show. Find the broken step and the picture comes back.
Related lessons: why a game judders when it can't keep up · how a game controller talks to a console · how a TV remote sends its buttons · why pictures go blocky.
Grown-up help on Tooltern: HDMI "No signal" fix, second monitor not detected, monitor stuck at 60 Hz, PS5 or Xbox HDR washed out or too dark. Glossary: EDID, HDCP, HDR, refresh rate, bandwidth.