Apple MD094LL/A Manuale Utente

iMac (27-inch, Mid 2010) Symptom Charts — Display 

 2010-09-09

Unlikely cause: camera, microphone

Noise / Unstable Flickering
•  Flickering image
•  Horizontal bands of static 

intermittently appear

•  Dock and / or menu bar shift 

positions

•  Display intermittently flashes 

on / off

•  Unstable image 
•  Humming noise from display
•  High frequency noise from 

display

1.  If display flicker only occurs when the brightness 

level is set below maximum, then jump to topic, 

“

2.  Run Automatic Software Update to verify that all 

available firmware 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.

1.  Verify if user issue is due to 

flickering, or to an unstable 

video image on the LCD.

Yes

Suspected flickering issue, go 

to step 2

No

For audible noise issues go 

to step 8. For all other issues 

go to appropriate symptoms 

flow.

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 

 symptom flow.

No

Video circuitry appears OK.  

Go to step 3.