PowerMac G4 switches off when set to sleep

Question

My venerable PowerMac G4 works just fine. However since a few weeks it switches itself off when put to sleep. The switch-off is a crash, like the power plug has been unplugged. An immediate restart doesn't work, the light just goes on for a second or two, afterwards the whole power vanishes again. After a few minutes the Mac can be normally restarted.
When left of the Mac works perfectly and doesn't crash at all.
Sounds to me like a certain power which is to be supplied by the internal power suplly just during sleep-mode is gone. Any ideas?
Thanks

Answer 1

hi,
thanks for your suggestions. I trashed the com.apple.powermanagement.plist file but there was no autowake file. The behaviour remained the same. I then reset the PMU as you suggested - still no change.
In the meantime I got another problem: the mouse is behaving erratically, the pointer is moving in jumps or not at all. The mouse shows the same behaviour when plugged in to my PowerBook - it must be faulty. I have just ordered a new Mighty Mouse to rule out any issue deriving from a broken mouse. I will also change the Lithium Battery on the motherboard even given the voltage is at 3,64 V, which should be sufficient.
Do you have any further suggestions?
Thanks in advance!
hi wolfman62--
i would try a couple of things. first, go to
/library/preferences and trash a couple of files in
the folder called systemconfiguration --
com.apple.powermanagement.plist and
com.apple.autowake.plist. then restart the
computer. test to see if there is any change. if
not, try resetting the pmu. to do this, shut off
all power to the computer and disconnect any
peripherals. then remove the power cord from where
it goes into the back of the machine into the power
supply. then remove the side panel and plastic air
deflector if your model has one. then look on the
bottom left corner of the logic board under the
bottom set of ram banks. there is a little square
with a button on it. (you might have to remove a
fan in order to find it.) ground yourself by
touching some metal and then letting go, and then
press the button on the logic board counting one one
thousand, and then release it. do not press it
twice as it can blow the chip. then put everything
back together and see if there is any difference.
let me know if either of those things makes any
difference. [ 8 ) ]