Logic board or screen problem?

I have an old MBP, which I decided to try and get working again. For some reason which I can't remember now I originally came to the conclusion that it was the logic board which was faulty. But now I'm beginning to wonder if it is the onboard screen.

When I start the machine it works well for a while - a variable period something less than two hours. Then it either reboots (this usually happens fairly quickly after starting) or the machine hangs. I cannot use any keys, nor the mouse, the cursor does not move, I cannot connect to the machine from another. The only recourse is to hold down the power button until the machine stops, then start it again.

I have been experimenting a little today, and I managed once to have the machine running from an external monitor with the onboard screen turned off. I only managed this once probably because I was then connecting the external monitor directly to the MBP (Now I have it connected via a KVM switch). However the machine appeared to work fine for somewhere around the two hour mark and then I discovered that it had rebooted, and was now showing the desktop on both screens. Since then I have not been able to get the machine to run with the onboard screen turned off.

Based on the above info, can anyone give me the probability that the problem is the logic board and built-in graphics card or whether it is more likely to be the onboard screen which is causing the problem.

Thanks in advance.

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James, there are several factors that you have mentioned that could be causing your problem. First and foremost it could be a heat issue and lack of air circulation inside of the computer beneath the logic board. If you have access to a small air compressor, close the lid and look for the air vents along the back edge of the laptop. Use the compressor to force air through the back side of the laptop. This should open the air vent grills inside of the computer to allow cooling air to pass through. If this does not work, then you need to remove the logic board and clean all of the dust out, in particular the the grill of the heatsink bracket. Once done then clean the heatsink compound of both of the heat sink pads and also the logig board and replace it with new Arctic Silver Heatsink compound. If you have already done this and you are still having a problem, I would then seriously suspect bad RAM chips. These will go bad and cause all of the same issues. Replace them one at a time with known good ones. I'm sure it is not the logic board as it is still functioning.

ED

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Thanks, Ed, for your suggestions on what could be the problem. A new update to this case, which I think supports your argument that it could be an overheating problem, quite apart from the fact that after googling, it seems that everybody and his brother who has an A1150 has had this kind of problem, is that I have now for two days had my machine running with this difference. Instead of it being on a wooden table or desk, it has been lying on a metal file cabinet, and it has run twelve hours or more each day without a problem. A metal surface will, of course, distribute heat away from the bottom of the machine much better than a wooden surface.

Unfortunately before I found out about the generality of this overheating problem, I had already bought a reconditioned logic board from iFixit, so now I'm going to strip the machine down and suck away the dust, then replace the heatsink compound, and I might as well use the new logic board since I have it. I'll be doing that during the weekend.

I'll post a result next week. Maybe I should invest in one of those metal holders for my MBP, the kind that holds the keyboard at a slight angle, just like a real keyboard. Some of them, I believe, have a small fan which blows air through the space under the machine.

Once again, thanks for your suggestions.

James

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