I had the same problem with a 933 Mhz ibook - i.e. screen freezing after a few minutes, sometimes not booting up and screen remaining blank. Took me a while to figure it out, as it appeared to be heat related - I could put an external fan on it and it would stay working for a lot longer. Thought it might be the internal fan not working, but I tested that (connected it to a battery) and that was working. The fault lies in the Graphics chip which sits under the larger second part of the heat sink. What happens is as the chip heats up, it starts to come away from the logic board (cracked solder perhaps?) and stops working. Not helped by the fact the logic board is very flexible at this point. The solution is to put a shim between the graphics chip and heatsink to keep the chip pressed hard on the board.(conveniently in this model the heatsink for the CPU is separate and does not require a shim) In the absence of any copper sheet, I found the ideal shim to be a 5 old half penny pieces (that is UK pennies as they are 1mm thick) liberally coated with heat sink paste. Result - I have a perfectly working ibook that has been working for a month now without any issues. Hope that helps.
crwdns2934105:0crwdne2934105:0
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crwdns2944067:03crwdne2944067:0
I think I have reset the PMU. System still freezes after 6-10 minutes. Then requires a period of shut down before a restart otherwise it goes into a blank blue screen. Note when it freezes there are a series of horizontal lines on the bottom third of the screen. My next move would be to reseat the Ram. Unable to do a reformat etc because I do not have the system disks.
Do you think this could be a fan issue.
crwdns2934271:0crwdnd2934271:0 Aston Ffrench crwdne2934271:0
whilst fiddling about with the GPU it ran hot, the fan ran non-stop but the display did not come on. Fiddled again, no fan, system started up display OK but froze again after 6 minutes.The moral..... the fan can run.
crwdns2934271:0crwdnd2934271:0 Aston Ffrench crwdne2934271:0
Reseated the Ram card. No change system still freezes after short period. Did notice that whilst monitoring Hd info... Under the heading More info the report was fetching. This status was never achieved ie the rotating symbol did just that ie it continually rotated.
crwdns2934271:0crwdnd2934271:0 Aston Ffrench crwdne2934271:0