Question toshibe l750 all good on battery but ac shuts off intermittently.

Jul 15, 2019
I'm troubleshooting a problem with a Toshiba L750.

Intermittent shuts off (immediate power cut and reboot) , 10, 20 , 30 + minutes after successful bootup. If AC is disconnected, battery powered works fine for hours on end.
It appears to be a problem with the AC supply and selection between battery and ac power circuitry. 3 different chargers have been tried. Its not the charger.

Even if the battery is in and the ac plugged in the power still cuts intermittently. The switching over to battery doesnt work after perhaps the computer senses an over voltage through current sensor or something like that. It could be the capacitors on the AC circuit are out of tolerance. It could be intermittent transistors on the ac input line. It could be the super IO doing its "thing."

The circuit is
AC goes through the usual fuse and filter(inductor/ caps) then
over voltage protection
current sense
then to the junction switch transistor which selects between battery or ac powered.

all controlled by the power/battery management chip.
I believe the super IO chip is involved aswell.

I've ordered a transistor repsonsible for switching at the battery/ac junction, along with a 6 pin dual transistor chip involved in that switching. I'll try replacing a few caps along the way too. 0.1UF 25 v. a few of those.

Which do you think is the likely culprit? Can SMD caps, chip type, have intermittent characteristics?

Tanks for any help and have a rippa week everyone.

P.S I do have a schematic, bit its not exact( different revision)