Direct answer
For the LG CX OLED TV, input selection, source output, cable, port and handshake should be tested in a direct minimal chain. First, connect one source directly with a known certified cable at standard resolution.
What this covers
- LG CX OLED TV (OLED48/55/65/77CX*)
- LG TV; OLED/QNED/LCD panel, webOS year, HDMI bandwidth and Magic Remote vary by model.
- The specific fault this record addresses: shows no signal on HDMI
What it does not cover
- ×The same symptom on a different LG product line, which has its own record and its own cited source
- ×An on-screen error code whose meaning has not been checked against this exact model's manual
- ×Live electrical, gas, sealed-system, internal battery-cell or structural repair — a technician boundary, not a self-service step
Differential
What actually causes this, and how to tell them apart
These are ordered by how often each one is the answer, not by how easy it is to try. The point of the middle column is that two causes producing the same headline symptom rarely produce the same detail — that detail is what tells you which one you have before you change anything.
- 1
The cable cannot carry the bandwidth being negotiated
What separates it No signal specifically at high resolution or high refresh rate, while lower settings work. Common when a 4K120 or 8K source is connected with an older cable.
How to confirm Bandwidth requirements rose sharply with HDMI 2.1. A cable that worked perfectly for 4K60 may fail entirely at 4K120. Test by lowering the source's output resolution — if the picture returns, the cable is the limit.
- 2
The port does not support the format being sent
What separates it No signal on one specific port while another works with the same cable and source.
How to confirm Most televisions support their highest bandwidth on only some ports, and the manual states which. A console set to 4K120 plugged into a lower-bandwidth port shows nothing at all.
- 3
The HDMI handshake has stalled
What separates it It worked yesterday, nothing changed, and now there is no signal.
How to confirm Power everything off, unplug the TV from the wall for 60 seconds, then power on the TV first and the source second. A stalled handshake is extremely common and this clears most of them.
- 4
An enhanced-format setting is enabled on a port that cannot sustain it
What separates it No signal after enabling an Enhanced, HDMI UHD Colour or Input Signal Plus setting for that port.
How to confirm These settings raise the bandwidth the port negotiates. Turning the setting off for that port restores a picture, at reduced capability.
- 5
A device in the middle of the chain cannot pass the format
What separates it No signal only when routed through a receiver, switch or soundbar, and fine when connected directly.
How to confirm Connect the source directly to the set as a test. The weakest device in the chain sets the ceiling for the whole chain.
- 6
Copy protection has failed to negotiate
What separates it A black screen or an HDCP error on protected streaming content, while menus and other apps display fine.
How to confirm That split — menus fine, protected content black — is characteristic of an HDCP failure, usually caused by an adapter, splitter or non-compliant cable.
Before you touch a setting
Record this first — changing settings destroys the evidence
Every item below stops existing the moment a reset, re-pair or settings change is made. Written down first, they are what separates the causes above; recovered afterwards, they are guesswork.
- Whether the problem follows the port, the cable, or the source when each is swapped.
- The resolution and refresh rate the source is set to output.
- Whether the port is one the manual lists as supporting that bandwidth.
- Whether menus display but protected content is black, which points at HDCP rather than bandwidth.
Power everything off, unplug the TV for 60 seconds, then power on the TV first
ReversibleA stalled HDMI handshake is one of the most common causes and this clears most of them.
Change one variable at a time: port, then cable, then source
ReversibleSwapping several at once produces a working picture with no idea which change fixed it.
Lower the source's output resolution or refresh rate as a test
ReversibleIf the picture returns, the cable or the port cannot carry the bandwidth the source was requesting.
Confirm the port supports the format, using the manual's port table
ReversibleMost sets support their highest bandwidth on only some ports.
Connect the source directly, bypassing any receiver, switch or soundbar
ReversibleThe weakest device in the chain sets the ceiling for the entire chain.
Model-specific
What is true of this model and not of its siblings
Generic advice for the product line fails here. Each item below is a property of this specific model family that changes which of the steps above apply to you.
- Model scope
- OLED48/55/65/77CX*. LG TV; OLED/QNED/LCD panel, webOS year, HDMI bandwidth and Magic Remote vary by model.
- Panel
- 2020 OLED (WOLED, pre-evo) with the Alpha 9 Gen3 processor — self-emissive, perfect blacks, no backlight. On a panel this age, faint uniform near-black variation and normal ABL dimming are expected, not defects.
- Smart platform
- The older webOS (2020 platform) with the Magic Remote. This is the oldest LG TV in this library, and app support is the key issue: some streaming apps have dropped or no longer update on this webOS generation. Check the LG Content Store first; where an app is gone, an external streamer is the fix, not a TV repair.
- Gaming / HDMI
- Four HDMI 2.1 ports at 4K 120 Hz with VRR, ALLM and G-Sync — but at 40 Gbps, not the 48 Gbps of later models, so a few of the most demanding 4K 120 formats (e.g. 12-bit) are outside its bandwidth. That is a spec ceiling, not a fault.
- Symptom boundary
- This record covers LG CX OLED TV when it shows no signal on HDMI. A different symptom on the same hardware, or this symptom on a different LG product line, has its own record with its own causes and its own cited source.
Stop boundary
When this stops being a self-service repair
Continuing past any one of these costs more than the repair saves — in safety, in warranty, or in evidence a technician needs.
- !Do not use HDMI splitters or adapters marketed as removing copy protection — they frequently cause the handshake failures they claim to solve.
Evidence ledger
Sources behind this answer
Visible sources support the visible claims. Home Product Support records the publisher, the fact used and the review date; community reports can suggest an issue but do not become a published fact on their own.
Where the manufacturer's article stops. LG Support publishes this as "TV and home theater support". Official LG television manuals, webOS support, diagnostics and repair entry point. What that article does not carry is the model boundary — it is written for a product line, and OLED48/55/65/77CX* is the scope applied here. Where a control label, terminal, indicator pattern or reset sequence differs on your unit, the manual for that exact model is the authority, not this page and not the article.
Exact questions
Common follow-ups
My LG CX won't run a streaming app any more.+
The CX is a 2020 TV on an older webOS, and the most common cause is the app provider ending support for that webOS version. Check the LG Content Store for an update and cold-restart the TV. If the app has been withdrawn for this generation of webOS, it cannot be restored on the TV itself — an inexpensive external streaming stick brings it back, which is far cheaper than replacing a working panel.
Does the LG CX do 4K 120Hz for my PS5?+
Yes — the CX has four HDMI 2.1 ports with 4K 120 Hz, VRR and ALLM. They run at 40 Gbps rather than the 48 Gbps of newer LGs, so the very highest-bandwidth 4K 120 formats fall outside its range, but standard PS5 and Xbox Series X 4K 120 gaming works. Use a certified cable and turn on Game Optimizer.
It worked yesterday and now says No Signal with nothing changed.+
That is usually a stalled HDMI handshake, and there is a reliable fix: power everything off, unplug the TV from the wall for a full 60 seconds, then power the TV on first and the source second. The order matters, because the display has to be ready to negotiate before the source starts trying.
My console shows no signal at 4K120 but works at 4K60.+
That is a bandwidth limit — either the cable or the port. HDMI 2.1 needs substantially more bandwidth than 4K60 did, so a cable that has always worked can fail completely at the higher mode. Check the manual for which ports support the full bandwidth, since most televisions only support it on some of them.
Does this answer apply to every LG model?+
No. It is scoped to OLED48/55/65/77CX*. LG TV; OLED/QNED/LCD panel, webOS year, HDMI bandwidth and Magic Remote vary by model.
What should I record before troubleshooting HDMI no signal or input?+
Record the complete model identifier, exact message or indicator, software/firmware where visible, the operating stage and what still works.
Why is a factory reset not the first step?+
A reset can erase accounts, networks, maps, schedules or preferences without distinguishing HDMI no signal, input. The ordered checks preserve that evidence.
When should I stop and use qualified service?+
Stop for hot connectors, bent ports, sparks or signal loss when a fixed port moves.
Answer for the exact device and software version shown above.