iMac (27-inch, Mid 2010) Symptom Charts — Display 55
2010-09-09
Noise / Unstable Flickering
Unlikely cause: camera, microphone
Quick Check
Symptoms Quick Check
Noise / Unstable Flickering
• Flickering image
• Horizontal bands of static
intermittently appear
• Dock and / or menu bar shift
positions
• Display intermittently ashes
on / o
• Unstable image
• Humming noise from display
• High frequency noise from
display
1. If display icker only occurs when the brightness
level is set below maximum, then jump to topic,
“Display: Backlight Issue / No Backlight.”
2. Run Automatic Software Update to verify that all
available rmware and software updates have
been applied.
3. Verify Mac OS X version installed is the build
version supported on the hardware. Make sure
customer didn’t migrate over old version of Mac
OS X.
4. Verify that intake vents on bottom of computer
are not obstructed.
5. Inspect system for third party software that is
being used to set fan speeds to a higher than
normal RPM. Some users may install this software
to monitor and control internal temperatures,
potentially causing higher fan speeds to generate
higher than expected noise levels.
Deep Dive
Check Result Action Code
1. Verify if user issue is due to
ickering, or to an unstable
video image on the LCD.
Yes Suspected ickering issue, go
to step 2
No For audible noise issues go
to step 8. For all other issues
go to appropriate symptoms
ow.
2. Connect a supported display
on rear Mini Display port
video port (Use known-good
MiniDisplay to VGA or DVI
adapters if needed). Verify
if issue occurs on both the
internal and the external
display.
Yes Suspect issue with video
circuitry. Go to Corrupted
Video symptom ow.
No Video circuitry appears OK.
Go to step 3.