Computer goes into random sleep and won't wake!

Question

This all started over a year ago, but I no longer remember what started it. After downloading an apple update my computer no longer goes into sleep mode on it's own. I have to manually put it to sleep. I tried every solution recommended...resetting everything, changing things in terminal, etc. I used a sleep assist program for a while but then I removed it b/c it was creating other issues. I finally just got used to doing it manually and lived with it.
Well, about 6mo ago (I cannot figure out why it started happening) my computer would just randomly go into a hard sleep mode. The screen goes black but I can still hear the computer running. NOTHING wakes it up. I have to shut down the computer holding the power button and then turn it back on. There seems to be no ill effects and I cannot figure out what is triggering it. I downloaded a cpu temperature program thinking that was it but it stays generally under 40C. It usually just happens while surfing the internet with only 1 or 2 tabs open. I generally only keep 3 programs running at a time (firefox, mail, itunes). It is totally random as I can go weeks without it happening but then yesterday it happened 4x in one day.
Help, I will try anything! Thanks

Answer 1

chic,
This could be caused by a dead PMU battery. This is from the service manual:
"Logic Board Battery
Important: Apple highly recommends removing the battery when handling the logic board. Make sure to use proper ESD protection when handling modules.
The battery on the logic board controls the stored system settings, such as date and time. It is only necessary to test the battery when you can’t power on the computer, or the date and time are
reset every time the AC power is removed.
The battery is also used to power the PMU chip (because the PMU chip keeps time and must always be running) when the computer is unplugged from the wall (AC power). The PMU is very
sensitive and touching any circuitry that is connected to the PMU can cause it to crash. If the PMU crashes, the battery life goes from about five years to about two days if the PMU is not reset. Once the battery goes dead, the PMU will reset the time and date every time the AC power is removed. To fix this situation, replace the battery and reset the PMU (refer to “Resetting the
PMU on the Logic Board” mentioned earlier in this chapter).
If the computer has a “No Power” situation, check the battery before replacing modules.
Testing the Battery
1. Remove the user access door on the bottom of the computer.
2. Locate the battery test point.
3. With the computer powered off, measure the battery voltage. Does the battery measure at least +3.5v?
If no, replace the battery and reset the PMU. If the battery measures +3.5v or higher, reinstall the battery and reset the PMU as above."
The battery test point is the lone one to the left and the ground point is just to the right of it.
Richard