The Hisense U8N's HDMI no-signal errors fall into two patterns: total black screen on every port (usually a TV or settings issue) and intermittent dropouts on HDMI 3 / HDMI 4 specifically (usually a cable or 4K@120Hz negotiation issue). Here is how to diagnose which one you have and fix it.
Quick answer
- Verify the port — only HDMI 3 and 4 are full HDMI 2.1 ports (4K@120Hz capable). HDMI 1 and 2 are HDMI 2.0 spec and cap at 4K@60Hz; a 4K@120Hz source plugged into ports 1 or 2 cannot negotiate and will fail.
- Replace the HDMI cable — Certified Ultra High Speed HDMI 48 Gbps. The cable in the box is fine; aftermarket cables under $15 often aren't.
- Power cycle for 30 seconds with the cable disconnected. Capacitors in the U8N's power supply need time to discharge.
- Set HDMI Format to "Enhanced Format" for the port you're using: Settings → Picture → HDMI Format
- Update firmware — Settings → System → Software Update → Network Update
U8N HDMI port layout (this trips up most users)
The U8N has four HDMI inputs but only two are full HDMI 2.1:
HDMI 2.0 ports (max 4K@60Hz; do not support 4K@120Hz):
- HDMI 1 — eARC port; 4K@60Hz max
- HDMI 2 — 4K@60Hz max
HDMI 2.1 ports (full 48 Gbps, required for 4K@120Hz):
- HDMI 3 — 4K@120Hz, VRR up to 144Hz
- HDMI 4 — 4K@120Hz, VRR up to 144Hz
If you plug a PS5, Xbox Series X, or high-refresh PC into HDMI 1 or 2, it cannot negotiate 4K at 120Hz on those ports — they max out at 4K@60Hz. Always use HDMI 3 or 4 for high-refresh game consoles.
Step 1: Cable and port test
Easiest fix first, biggest cause:
- Swap the cable for a Certified Ultra High Speed HDMI cable (look for the holographic certification sticker on the box). Older "High Speed" or "Premium High Speed" cables work for ARC but fail at HDMI 2.1 bandwidth.
- Move the source device to a different HDMI port. If a 4K@120 source is on HDMI 1 or 2, move it to 3 or 4. If a basic 4K@60 source has been on 3 or 4, try 1 or 2 — sometimes the 2.1 ports are more sensitive to weak HDCP handshakes.
- Reseat both ends of the cable. Even a millimeter of disconnection breaks signal. Press until you feel the connector click.
If swapping cables fixes it, you're done. If swapping ports works, your TV may have a failing port — note which.
Step 2: Set HDMI Format to Enhanced
The U8N defaults the HDMI 2.1 ports to "Standard Format" until you opt-in. Standard Format caps the port at HDMI 2.0 behavior even on the 2.1 ports.
- Settings → Picture → HDMI Format
- Select the port your source is on (HDMI 3 or 4)
- Set to Enhanced Format
Without this enabled, you'll see "no signal" with 4K@120 sources or get capped at 4K@60.
Step 3: Full power cycle
If the cable and port settings are correct but you still see no signal:
- Turn off the TV via remote
- Unplug the HDMI cable from both ends
- Unplug the TV from wall power
- Wait 30 seconds (the U8N's power supply has capacitors that need to discharge — under 30 seconds doesn't fully clear the HDMI handshake state)
- Plug TV back in, power on
- Reconnect HDMI cable to the same port
- Power on the source device
This sequence resets the HDCP handshake state. Many post-firmware-update no-signal errors clear here.
Step 4: Check the source device's resolution output
The U8N can display "no signal" if the source is outputting a resolution the TV can't accept on that specific port:
- PS5 — Settings → Screen and Video → Resolution → set to "Automatic" or 4K
- Xbox Series X — Settings → General → TV & display options → 4K UHD, 120Hz, ensure "Allow 4K" is on
- PC — set the GPU output to 3840×2160 at 60Hz first; once it works, raise to 120Hz
- Cable / satellite box — set to 1080p or 4K@60 (these boxes are typically HDMI 2.0 only)
A handshake-failed input usually means the source is asking for a mode the port can't deliver. Drop the resolution one tier and re-test.
Step 5: Check HDMI Diagnosis (built-in tool)
The U8N includes an HDMI diagnostic mode:
- Settings → Support → Self Diagnosis → Picture Test
- Run the test — if the test pattern displays, the panel is working
- Settings → Support → Self Diagnosis → Signal Information
- With the source connected, this shows the negotiated resolution, refresh rate, and color format
If Signal Information says "no signal" with the source clearly outputting, the port itself is failing. If it shows a different resolution than expected (e.g., 4K@60 when you expect 4K@120), the cable or HDMI Format setting is the issue.
Step 6: Update firmware
Hisense issues regular firmware updates that fix HDMI compatibility issues, especially around HDMI 2.1 negotiation.
- Settings → System → Software Update → Auto Update: turn on
- Settings → System → Software Update → Network Update: check now
If the U8N has been offline for a while, it could be 6+ months out of date — that alone has caused many no-signal complaints with newer console firmware.
Step 7: Disable HDMI-CEC (CEC) temporarily
Hisense's CEC implementation can occasionally lock a port into a mismatched state when multiple CEC devices are on the bus.
- Settings → System → HDMI & CEC → CEC Function: Off
- Power cycle source devices
- Test HDMI signal
- If signal returns, turn CEC back on but disable CEC on connected devices one at a time (PS5, Apple TV, soundbar) to find the conflicting one
Step 8: Test with a different source
Isolate where the failure is:
- Disconnect all other HDMI sources except the one that has no signal
- Try a different known-good source (different streaming device, console) on the same port and cable
- If the new source works, the original source is the problem
- If the new source also fails, swap the cable
- If swapping the cable also fails, swap the port. If still no signal — the port has failed
When the TV itself is failing
If you've tested:
- Multiple cables (one of them certified)
- Each HDMI port (1, 2, 3, and 4)
- Multiple source devices
- Power-cycled and updated firmware
…and nothing works, the TV's HDMI board may be failing. Hisense U8N has a 1-year warranty plus extensions through retailers (Costco offers 5 years; Amazon's 4-year protection is common). Symptoms that point to hardware failure:
- All HDMI ports show no signal simultaneously
- Random reboot when an HDMI cable is connected
- Visible buzzing from the back of the TV when an HDMI device is plugged in
- Picture appears for a few seconds, then drops
Contact Hisense support with serial number, firmware version, and a video of the symptom.
FAQ
Why does HDMI 1 work but HDMI 3 doesn't on my U8N? HDMI 3 is HDMI 2.1 — more demanding electrically. Lower-quality cables work on HDMI 1 (2.0 spec) but fail on HDMI 3 at 4K@120. Cable is almost always the culprit.
Does the U8N support Dolby Vision over all HDMI ports? Yes. Dolby Vision is a content format, handled by the panel rather than a specific port spec. Every input on the U8N can display Dolby Vision at the resolutions it can handle: HDMI 1 and 2 at 4K@60Hz max, HDMI 3 and 4 up to 4K@120Hz.
Can I use HDMI 1 (the eARC port) for a game console? You can but it caps at 4K@60. The eARC port is HDMI 2.0 spec on the U8N. Use HDMI 3 or 4 for the console and let HDMI 1 handle eARC to the soundbar.
Will the eARC port work if I use a non-certified HDMI cable? For ARC (Dolby Digital 5.1), yes. For eARC (Dolby Atmos lossless), you need a Certified Ultra High Speed HDMI cable. Atmos drops to "PCM" or "Dolby Digital" on the soundbar are usually a cable issue.
Why does the screen flicker when my PS5 negotiates 4K@120 on the U8N? Hisense's Game Mode HDR on the U8N occasionally has handshake glitches at 4K@120. Update firmware first; if it persists, try setting the PS5 to 4K@60 and confirm flicker stops, then step up.