iMac Display Lines & Artifacts
iMac • Display lines, artifacts, or garbled screen
Quick Answer
Lines and visual artifacts on an iMac display are typically caused by a failing GPU (especially on 2009-2015 models with discrete AMD/NVIDIA GPUs), a damaged display panel, or a failing TCON (timing controller) board within the display assembly. If the artifacts appear during startup before macOS loads, it is almost certainly hardware.
Possible Causes
GPU failure (discrete GPU models)
Very common (older models)iMacs from 2009-2015 with discrete AMD or NVIDIA GPUs are prone to GPU failure from thermal stress. Symptoms include colored lines, artifacts, garbled display, kernel panics, and the screen going black.
Failing display panel
ModerateThe LCD panel itself can develop faults that produce lines (usually consistent, thin lines that do not move) or color banding. This is a panel hardware issue, not GPU.
TCON board failure
Less commonThe timing controller board inside the display assembly manages signal timing. A failed TCON can produce horizontal or vertical banding, partial display failure, or a blank screen with backlight.
Display cable issue
Less commonThe cable connecting the logic board to the display panel can develop faults from heat or age, causing intermittent lines or partial display failure.
Software or driver glitch
UncommonRarely, a macOS graphics driver issue can cause artifacts. If the issue only appears after macOS loads (not during startup), try Safe Mode to rule out software.
What You Can Try at Home
Check if artifacts appear during startup
Restart the iMac and watch carefully. If lines/artifacts are visible on the Apple logo screen (before macOS loads), the issue is hardware — GPU, panel, or cable. Software cannot cause artifacts during firmware boot.
Boot into Safe Mode
Intel iMac: Hold Shift during startup. If artifacts disappear in Safe Mode, a software conflict is possible (though unlikely for persistent artifacts). If artifacts persist in Safe Mode, it is hardware.
Reset NVRAM
Shut down, press power, immediately hold Option+Command+P+R for 20 seconds. This resets display settings and VRAM, which can resolve some display glitches.
Connect an external display
Use HDMI or Thunderbolt to connect an external monitor. If the external display shows the same artifacts, the GPU is failing. If the external display is clean, the issue is the internal panel or cable.
Note the artifact pattern
Consistent thin lines in the same position = panel issue. Moving/flickering artifacts, colored blocks, or garbled text = GPU issue. This helps a technician diagnose remotely.
When to Get Professional Help
If artifacts are visible during startup (hardware confirmed), persist through Safe Mode and NVRAM reset, or appear on both internal and external displays (GPU failure), professional repair is needed. iMacs should not be opened by untrained individuals — the display is bonded with adhesive.
WarriorMac Repair Cost
GPU repair (component-level): from $199. Display panel replacement: from $125. Free diagnosis.
Frequently Asked Questions
Is GPU failure common on iMacs?
On 2009-2015 iMacs with discrete AMD or NVIDIA GPUs, yes. These GPUs were prone to thermal-related solder joint failures. Apple Silicon iMacs (M1/M3/M4) have integrated GPUs that are significantly more reliable.
Can an iMac GPU be repaired without replacing the logic board?
In many cases, yes. Component-level repair can address GPU solder joint failures and supporting component issues. For some models, GPU reballing or replacement is possible. We assess each case individually.
How do I tell if it is the GPU or the display panel?
Connect an external monitor. If the external shows the same artifacts, the GPU is failing. If the external is clean, the issue is the internal panel, TCON, or cable.