Apple MD094LL/A manual Symptoms Quick Check Noise / Unstable Flickering

Noise / Unstable Flickering

Unlikely cause: camera, microphone

Quick Check

Symptoms	Quick Check
Noise / Unstable Flickering	1.	If display flicker only occurs when the brightness
• Flickering image		level is set below maximum, then jump to topic,
• Horizontal bands of static		“Display: Backlight Issue / No Backlight.”
intermittently appear	2.	Run Automatic Software Update to verify that all
• Dock and / or menu bar shift		available firmware and software updates have
positions		been applied.

•Display intermittently flashes 3. Verify Mac OS X version installed is the build

on / off	version supported on the hardware. Make sure
• Unstable image	customer didn’t migrate over old version of Mac
	OS X.
• Humming noise from display
	4. Verify that intake vents on bottom of computer
• High frequency noise from
display	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	Yes	Suspected flickering issue, go
	flickering, or to an unstable		to step 2
	video image on the LCD.
		No	For audible noise issues go
			to step 8. For all other issues
			go to appropriate symptoms
			flow.
2.	Connect a supported display	Yes	Suspect issue with video
	on rear Mini Display port		circuitry. Go to Corrupted
	video port (Use known-good		Video symptom flow.
	MiniDisplay to VGA or DVI
		No	Video circuitry appears OK.
	adapters if needed). Verify
			Go to step 3.
	if issue occurs on both the
	internal and the external
	display.

2010-09-09 iMac (27-inch, Mid 2010) Symptom Charts — Display  55