Summary

"No signal" (sometimes shown as a black screen, a red "X", or "video loss") is one of the most common CCTV callouts, and it is rarely the camera itself. The message simply means the NVR or DVR channel is not receiving a usable video stream — the cause could be anywhere in the chain from the camera's image sensor through its cabling, power supply, and network path to the recorder's processing of that channel.

Modern UK domestic and small commercial CCTV is almost entirely IP-based: cameras connect via CAT5e/CAT6 cable carrying both data and power (PoE — Power over Ethernet) to an NVR or PoE switch. Older and some retrofit systems remain analogue, using RG59 coaxial cable for video and a separate 12V DC feed for power, terminating at a DVR. The two technologies fail differently, so the first diagnostic step is always establishing which type of system you are working on.

The single biggest cause of "no signal" call-outs on IP systems is a cable or connector fault — RJ45 crimps working loose, cable runs exceeding the 100m Ethernet limit, or moisture ingress at an outdoor gland. On analogue systems, it is almost always a power or coax connector issue rather than a camera fault. Genuine camera hardware failure (dead image sensor, failed PCB) is a real possibility but should be the last thing you suspect, not the first — swap the suspect camera onto a known-good port/cable before condemning it.

Key Facts

Quick Reference Table

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Symptom System Type Most Likely Cause First Check
Total black screen, no signal icon IP No power at camera / bad PoE port Swap PoE switch port
Total black screen, no signal icon Analogue Loose/corroded BNC connector Re-terminate BNC connector
Signal drops in/out intermittently IP Cable run too long, marginal PoE budget Check cable length, PoE wattage total
Signal drops in/out intermittently Analogue Damaged coax, water in connector Inspect and reseal connector
Camera reboots every few minutes IP Insufficient PoE power, firmware fault Check PoE budget, update firmware
One channel always blank, others fine Either Channel disabled/licence limit on NVR Check NVR channel configuration
All channels blank simultaneously Either NVR/DVR power or storage fault Check NVR power, HDD status
Distorted/rolling image, not black Analogue Format mismatch (AHD/TVI/CVI) Match camera and DVR channel format
Signal lost after router/switch reset IP DHCP lease change, IP conflict Assign static IP, check for duplicates
Signal lost after recent storm/rain Either Water ingress at gland or joint Inspect and reseal outdoor connections

Detailed Guidance

Fault-Finding Decision Tree

START: NVR/DVR channel shows "No Signal"
│
├─ STEP 1: Is it ONE camera or ALL cameras?
│   ├─ ALL cameras → Fault is at the NVR/DVR, not the cameras
│   │   ├─ NVR won't power on → Check mains supply, PSU, fuse
│   │   └─ NVR powers on but all channels blank → Check HDD status,
│   │       firmware, factory reset as last resort
│   └─ ONE camera (or a few) → Continue to Step 2
│
├─ STEP 2: What type of camera/cable?
│   ├─ IP camera (CAT5e/CAT6, PoE) → go to IP branch
│   └─ Analogue camera (BNC coax) → go to Analogue branch
│
├─ IP BRANCH
│   ├─ Check link light on switch/NVR port for that camera
│   │   ├─ No link light → cable/connector fault or camera dead
│   │   │   ├─ Swap camera to a known-good port with a known-good
│   │   │   │   patch cable → link appears? → original port/cable faulty
│   │   │   └─ Still no link → check camera locally (12V bench PSU
│   │   │       + direct laptop connection) → suspect camera hardware
│   │   └─ Link light present, still no signal → check camera IP
│   │       ├─ Ping the camera's configured IP
│   │       │   ├─ No reply → IP conflict or DHCP change; check
│   │       │   │   camera's actual IP via discovery tool
│   │       │   └─ Replies → camera is on the network but not
│   │       │       registering with NVR → check ONVIF/RTSP
│   │       │       credentials, re-add camera to NVR channel
│   └─ Check PoE budget: total camera wattage vs switch/NVR rating
│       └─ Over budget → camera brownouts under load, especially
│           with IR illuminators active at night
│
└─ ANALOGUE BRANCH
    ├─ Check 12V DC power at camera end (multimeter at connector)
    │   ├─ No voltage → check PSU, fuse, cable continuity
    │   └─ Voltage present → power is not the issue, continue
    ├─ Check BNC connector for corrosion/looseness (both ends)
    │   └─ Re-terminate if corroded — do not just reseat a
    │       corroded connector, cut back and refit
    ├─ Check DVR channel video format setting (AHD/TVI/CVI/CVBS)
    │   └─ Must match camera output format exactly, or image
    │       will be blank, rolling, or badly distorted
    └─ Swap camera to a known-good DVR channel/cable to isolate
        camera vs cable vs DVR channel fault

Isolating IP Camera Faults

The fastest way to isolate an IP camera fault is substitution testing, working from the recorder outward:

  1. Swap the suspect camera's patch lead at the NVR/switch end with a cable known to work. If the link light appears, the original cable or its termination was the fault.
  2. Move the suspect camera to a different, known-working port on the switch/NVR. If it now shows signal, the original port or that section of the run is faulty.
  3. Bench-test the camera — power it directly from a 12V/PoE injector and connect a laptop with a network scanner or the manufacturer's discovery tool. If the camera responds, the fault is in the fixed cable run, not the camera.
  4. Check camera event/system logs if accessible — many IP cameras log reboot events, power-loss events, and network disconnects, which point directly to power or link instability rather than a hardware failure.

Cable faults on external runs are disproportionately common at three points: the gland where cable enters the camera housing (water tracking down the cable into the connector), any junction box used to extend a run (corrosion, poor crimps), and points where cable passes through masonry or is clipped externally (crushing, UV degradation of cheap outdoor-rated cable, and rodent damage in lofts).

Isolating Analogue Camera Faults

Analogue systems fail most often at the BNC connector rather than in the cable itself. A poorly terminated or corroded BNC connector will show as intermittent, snowy, or completely absent signal, and can look exactly like a dead camera on the DVR display.

  1. Check power first — a 12V DC multimeter reading at the camera end confirms the power side of the circuit. No voltage means checking the PSU output, in-line fuse, and continuity of the power core back to source.
  2. Check the video core separately — coax faults and power faults are independent; a camera can have good power and a faulty video connection, or vice versa.
  3. Re-terminate rather than reseat any connector showing green or white corrosion — the corrosion increases resistance across the joint and will recur even after cleaning.
  4. Confirm the DVR channel's video standard matches the camera (AHD, TVI, CVI, or plain CVBS/analogue). Mixing formats on a hybrid DVR is a common installer error, especially when replacing a single camera on an existing multi-format system.

NVR/DVR-Side Causes

If every channel on a recorder shows no signal simultaneously, stop looking at the cameras — the fault is almost certainly the recorder or its power/storage:

Preventing Recurrence

Frequently Asked Questions

Why does my camera show a signal during the day but drop out at night?

This points to a power budget issue. Most cameras draw noticeably more power at night when their infrared (IR) illuminators activate — if the PoE switch or NVR is close to its power budget limit during the day, the added IR draw can push it over, causing the camera to brownout or reboot. Check the total PoE wattage of all connected cameras against the switch/NVR's rated budget, and check for voltage drop on long cable runs, which also gets worse under higher current draw.

Can a bad HDD in the NVR cause "no signal" on a camera channel?

Not directly — a failing hard drive affects recording and playback, not the live video signal from a camera. However, some budget NVRs behave erratically or freeze channels when the HDD is failing or full, which can present as a no-signal or frozen image on affected channels. If all channels are affected together and the cameras test fine individually, check HDD health before chasing camera or cable faults.

Is it worth repairing analogue coax runs or should I upgrade to IP?

For a single fault on an otherwise working analogue system, repair is usually the pragmatic choice — re-terminating a BNC connector or replacing a short damaged section of coax is quick and cheap. If you are already opening up cable routes, or the system has multiple recurring faults, it is worth quoting for an IP upgrade: CAT6 with PoE carries power and data in one cable, gives significantly better resolution, and removes the format-mismatch failure mode entirely. Existing coax routes can sometimes be reused as a draw-cord for pulling new CAT6.

The camera image is visible but very dark, grainy, or washed out at night — is that a "no signal" fault?

No — that is an image-quality issue, not a signal-path fault, and has different causes: dirty or scratched IR-cut filter, cobwebs across the lens (very common), incorrect exposure/gain settings, or IR illuminators reflecting off a nearby wall or window (common when a camera is mounted too close to a reflective surface). Clean the lens and housing first, then check the camera's exposure and IR settings in its web interface before assuming a hardware fault.

Regulations & Standards