laptop motherboard problem !

Sounds like the power button is jammed or broken, does the power button do anything when there is only the battery is plugged in?
Does it do anything once the laptop is on?

My guess is that the button is either stuck on and when you plug in the power cable it sends the signal to power up.
OR
Something with the switch from battery to plug is sending a signal for some reason through the power button

 

I'd go with GreenGiant's checks first.
Other possibility is a broken power jack on the laptop, that is shorting connections
to input power/switching.

 

i have the same problem as you, and this seems to be a rare one as no much data about it over net.
i have the motherboard out and the launch board out so i excluded the jammed power button thing
the weird thing is when plug the ac adapter jack it power on the motherboard without any interference then keep it running for 5 seconds then shut down by itself

can a broken power plug cause this?
or what to test then?

 

Verify that the one side of the switch is 'high' and the other 'low'...

Pressing the button pulls the 'wake' line low (aka grounds it) and this is what turns on the computer... If a short (failed part) is pulling the line low or the pull up is not doing it's job of pulling that line high it will act as if the button is always pressed...

 

the launch board with the power button was tested on another motherboard and it work well

 

That doesn't address what I suggested you look at... The 'wake on press' function will be part of the motherboard/power supply logic not part of a button sub board...

 

ok i get you , i will try to check , thanx in advance

 

ok. There is a short circuit of the power switch terminal. Locate it on the board and seperate it.

 

ok after checking removed the power jack and reapply it the issue changed , now the power is on for 5 seconds then off and if press on again the same happens , meanwhile the processor fan is not getting power as it doesnot turn on while the fan itself is checked and working fine
where to go now?

 

Power on problem

At this juncture, make sure your RAM is good and it's connected on the motherboard before power on as well as the hard disk.

 

the hard disk is ok and the ram is ok both tested and both installed with no change

 

try to check cmos battery then try tu plugin without it.

 

Welcome to EP Mac, but did you check the date of this thread?

 

Does it work correct on the battery and not pluged in..?, if so swap the power supply they go crap and cause all kinds of intermitante problems.

 

Doc, did you notice this thread is ~7 years old?

 

No, lol but will watch a little better, but its cause im 7*9