inspirion 1150 not posting..

[clueless2]

Here is my problem and have been working at it for sometime now with no obvious solution in sight..apart from sourcing a cmos battery..

On boot up, no post and no beep code ..runs for 15 sec and powers down..
I swapped memory and cpu with working cpu and memory ..no difference.

Tested cmos battery: 2.75v, it is low but even so, this wouldn't be the cause of it powering down after 15secs..
I have removed drive, cd, display etc... it is stripped down to bare bones: cpu, mem, keybrd and vga monitor.

Overheating? I have removed heatsink and cleaned it, removed cpu and reinstall making sure it is sitting in the socket (478) reapplied thermal grease and reassembled the unit, repowered ..fan is switching on that's all, no other sign of life and then cuts out 15sec later.

No posting or beep code could be explained by low cmos battery [cmos config not stored or blanked out in nvram, but doesn't explain the cpu fan cutting out after 10-20sec..
No reset switch, the closest is to power off and hold the power on switch for 10sec, not success either..

Also tested with ac power unit only, battery only, with both etc.. no success.
No power_good signals caused by low voltage in cmos battery perhaps?

Anyone came accross this problem before?

[mairving]

Most likely a bad system board. Unless you can find a used board then it would be too expensive to replace.