Late 2007 MacBook Pro intermittent black screen

Question

I have this very odd issue with an intermittent black screen on a late 2007 MacBook Pro (4GB/320GB 7200rpm) Mac OS X 10.6.8 v1.1
Apologies for the length of the post.
In cycles separated by a few days to a week, the screen will flicker to black, initially very briefly, then for longer periods until it is black continuously, where it stays from a few hours to a couple of days then it flickers to normal, again very briefly then with longer intervals until it is steady and normal. It can then be fine for a week or more.
When the screen is working, it's perfect; no lines, stripes, colour shift or any difference to what one would expect. When it is black, the backlight is still operational (and dimming when on battery power) but there is no image - all pixels are solid black. Shining a torch on/through the screen does not reveal any image. When mirrored, the external monitor shows the brightness adjustment moving up and down in response to the key presses but it has no effect on the internal screen.
My external display (Eizo) is always functional no matter what the built-in one is doing and is completely solid at all times.
There is no correlation to temperature (I have SMC fan control), sleep, restart, fan speed, power source or anything environmental. The MacBook is on a fan stand for most of the time. External connections make no difference. If the fault is present before changing any of these factors, it is there after.
I am aware that this machine has known vulnerabilities with GPU and display issues but none present quite like this. I have performed the usual trawl on the net and I now know more than I ever wanted to about attempts to fix it.
Software remedies attempted:
Resetting PRAM and power manager.
No sleep image file (never used this option). I deleted the old swap files that were there in any case but this unsurprisingly did nothing.
Resetting the display settings via keyboard commands or Sys Prefs.
Screen savers and settings are not implicated.
Nothing whatever in the console logs that I can see.
TechTool Pro gives video RAM a clean bill of health and all other components pass including tests on the HD with TTP and DiskWarrior.
Safe boot and booting from systems on backups seem to have no effect but one safe boot restored the screen briefly - I think it was a coincidence.
I updated the OS from 10.6.6 to 10.6.8 while this fault was coming and going and it made no difference. I usually prepare the machine for updates by running the cron jobs, repairing permissions etc.
In expectation of suffering this fault when the external monitor was not connected, I installed iScreen on the MacBook and use my iPad as a supplementary display and that works well too. Having all three operating, when the internal is functioning, is quite fun.
Hardware tests:
I removed the upper plate holding the keyboard and the interior of the machine was very clean with only some small dust accumulations in the fans, which were removed. There was no sign of any discolouration, corrosion, or other unpleasantness on the PCBs. All connectors and wiring looked good.
Every part of the logic board, cables and connectors were percussed, gently deflected and spray freezed, both while the fault was present and not (machine running) with no effect.
Display back was removed and the LCD board given the same treatment. No changes.
Display cable disconnected at both ends and tested for continuity (probe resistance accounted for) and consistency with a Fluke 87 multimeter - passed OK. On a scope, active signals and power were present on all the pins when the display was working but the fault did not occur during this test, which might have been interesting.
No apparent shorting of the display cable but without removing it this cannot be proved.
Problem not affected by hinge position, pressure on any part of the display, twisting, percussing etc.
Used compressed air to blow out the connectors which were reseated carefully.
After all this, the machine remains in exactly the same state, cycling between operational and black with various flickering stages as it comes and goes.
All I can deduce is that as the external monitor has always been OK, the GPU itself is probably working fine and the fault is more likely in the LCD panel electronics. I doesn't feel like a software issue to me but heck, I don't know what is going on.
Does anyone have any experience of something like this?
Thanks,
Joel.

Answer 1

Thomas,
Thanks for your post and I'm sorry you have suffered the same problems.
My trust levels are not very high because it's clear there is some systemic display problem with this model, which is why Apple are fixing them. As I mentioned, we have no idea if the replacement boards are any different to the originals. From your experience it would look like they are not and my suspicion is that it is very unlikely that Apple made a new batch of these logic boards a long time after the model was discontinued. If anyone has evidence to the contrary, I stand to be corrected.
As you say, the difference between our two faults appears to be that a physical deformation of some part of the machine does something with yours but never did with mine. At one point I felt that a short in the internal display cable seemed like the best explanation for the problem but it looks like it's more complex than that because of the behaviour of our external displays and subsequent strange booting behaviour.
If, as I have read, the soldering of the GPU was faulty and leads to progressive failure of the graphics sub-system, then all kinds of strange behaviours could arise and produce the intermittent problems we have seen. Micro-fractures of the chip interconnects would suggest that tiny movements might change the presentation of the fault. If soldering really is the issue, then keeping the machine as cool as possible will extend the life of the connections. Consequently mine will sit on a fan-stand for the rest of its days, which is no problem because it just had Win 7 installed on it and I don't want to be seen in public with it in that state ;-)
All we can conclude is that a logic board swap fixes the problem for some indeterminate period, so the problem is on that board. Whether it is a design fault with the NVIDIA chip itself or a manufacturing fault with the board is not clear but we can probably forget LCD panels, cables, sleep issues, power supplies and all the other peripheral issues unless there is yet another design issue that causes the GPU to fail.
Are you intending to present your machine to Apple for another go at a fix?