17" unibody MacBook Pro Flickering -Explanation

Question

Like many other users here I have been experiencing flickering on my new 17" MacBook Pro when the display is set to low brightness settings. In my case the screen flickers whether running off battery or off the wall, and whether the battery is full or not. However, after conducting some tests I believe that all instances of this screen flicker stem from the same root problem.
My screen flickers more at certain times than at others. The first thing I did was try to isolate what made the flickering more severe. In my case, this is what I found
1)whenever the cpu is under heavy load
2)whenever any peripherals, especially bus-powered ones, are connected to the usb or firewire ports
3)whenever there is heavy disk activity on the internal HDD
4)when connecting or disconnecting the magsafe (screen flickers violently for 2-3 seconds!)
Bus-powered peripherals draw power from the laptop in order to run. The more devices I have hooked up to my machine, the more the screen flickers- in the case of a usb hub or daisy chained firewire, adding more devices does not draw more voltage (because it is all parallel) but it certainly draws more current. This is in effect robbing the LCD of amperage, causing the flicker.
CPU load works the same way. Intel has a technology called SpeedStep that they've implemented on all their mobile CPU's. The way SpeedStep works is that it dynamically scales the frequency of your CPU so that if you aren't demanding much of the system, the CPU is downclocked to reduce power draw and save you precious battery life. As you make increasing heavy cpu load requests, the SpeedStep throttles the CPU upwards which increases the voltage it draws. We're only talking about a difference of about .75 volts, but it seems that is enough to produce more violent flicker as the LCD becomes starved for power.
HDD activity is the same thing. The servos that move the head and spin the disk all draw power when they are moving. Although I haven't tried it yet, some users here have reported worse flickering when loading/reading from the optical drive, which again suggests a power issue. Obviously disconnecting and reconnecting the magsafe cycles the computer from battery to AC, which is clearly power related (although I am not sure exactly how yet).
Some component is failing (a switched or linear regulator or diode most likely) that is making our machines unable to handle any current draw whatsoever. Because they cannot keep up with the demand for amperage, the voltage in the machine fluctuates and drops below the proper level, producing the flicker.
I'm not sure exactly why the flickering is only visible on low brightness settings; there could be a number of explanations, including the fact that the flickering is subtle enough that the difference between max brightness and slightly-less-than-max brightness is not detectable by the eye, whereas the difference between low brightness and lower brightness is. I have a theory that is pure speculation on my part, but I'll include it here in case anyone more knowledgeable about displays can comment on its likelihood. As I understand it, the LED's rapidly oscillate between on/off states to produce the illusion of low brightness. In order to trick the "refresh rate of our eyes," these oscillations must be very precise. Perhaps the fluctuating voltage levels in the machine are throwing off the clock controlling these oscillations.
In any case, I would guess that the flickering screen is merely a symptom of a much deeper systemic problem effecting every module in the machine. If dirty power is running around everywhere, this is not good. This would effect every component down the power rail. I would not wait to exchange these machines.
The good news is that Apple Engineering is aware of this problem and are anxious to get affected machines back to isolate exactly what is going wrong. I wouldn't bother going to the genius bar as they have no idea what is going on and generally have no grasp of the architecture of these machines anyway- if it's not a problem they can resolve in the GUI, they are completely useless. Just call Apple Care and escalate it past the subordinates who will tell you that you just need to reset the PRAM or wait for a firmware update (all lies btw). Once you get to someone at a hight level they will give you the straight dope and set up a replacement.
Hope this was helpful!
Message was edited by: JordanBartee
Message was edited by: JordanBartee

Answer 1

Interesting theory, but I'm running a powered USB hub, so I'm not drawing down the USB ports and connecting/disconnecting magsafe also doesn't trigger the problem. I do have many FW drives daisy-chained, but none are bus powered.
It's not a backlight issue - when it's not affecting the entire screen, it looks like a GUI redraw problem. The whole screen flash could be the backlight going off/on, but it doesn't look like it to me.
I've seen the flash and flicker at various screen brightnesses, so it doesn't seem related to low brightness. I spent a day or more importing CDs, which although isn't a super high cpu load, it was enough to bring the temps up. Internal HD was cranking away, too, and I had no symptoms of the problem.
When I got to my machine this morning, and woke the display [only], I got both the full screen flash and the partial redraw flash/flicker [lower 1/4 or so of screen].
Over the last couple of days, waking from sleep seemed to trigger the problem. The resolution seems to be a restart and/or powerdown, then restart. Though I've seen the problem on both GPU's, it seems more prevalent on the 9600M, but I don't have any data on it yet.
I've started a log for tracking when the problem occurs, under what conditions (including last app used), and what I did to attempt to "fix" the problem.