Hi, I have a Toshiba Satellite L300 Laptop thats shuts down, restarts or freezes whenever the ac plug is connected. Works fine on battery power and charges ok with laptop closed up or turned off when i connect adopter. i am also chip level technician .can anybody help me ?

It sounds as if you need a new charger. Try removing the battery and start the machine with just the charger. If that works then it may be a new battery you need. Some toshiba notebooks have a 'power saver tool' preinstalled, which is used to monitor battery performance. You can download a copy here:
http://eu.computers.toshiba-europe.com/innovation/download_drivers_bios.jsp?service=EU
Not sure if it will be compatible with your machine, but maybe worth a try as it could be a corrupt program causing the problem.

right off the bat, i would suspect a bad power adapter for the computer. or perhaps a faulty computer. your best bet is to call toshiba and talk to them directly.

Many models of Toshiba Satellite laptops have a capacitor called NEC/TOKIN Proadlizer which loses its capacitance with time and hence laptop freezes, shuts down or restarts when AC is plugged in. One needs to replace this cap as shown here:
http://gs138.photobucket.com/groups/q251/S1BXDWUERU/

Problem description: The laptop shuts off when AC power adapter is plugged in. The laptop works fine on battery power but as soon as you connect it to AC adapter, the laptop turns off.
Possible cause: 1. Power adapter failure.
2. Motherboard failure.
Possible troubleshooting steps and repair solution: First of all, test the power adapter. Make sure the adapter outputs correct voltage. It's possible that the output voltage is not correct and the laptop shuts down to prevent the damage. Test your laptop with another known good power adapter.
Toshiba Satellite A305 AC Adapter
If the problem still exists, even after replacing the adapter, most likely it's the motherboard failure. Replace the motherboard.

Replace the AC Adapter, (ebay from £10.00).
Did it come with XP on it? Mine came with Vista and there are conflicts with XP and graphic adapters. There is no XP driver for the ATI adapter in mine.
Go online to Toshiba and download all of the updated drivers that you require. A user friendly system.

you should have your unit check professionally, as it can be cause by multiple problem.

1. laptop fan
2. memory problem
3. voltage problem.

either way, its best that you try to have it check thru the toshiba service center.

Hi ; the system restart if the power level is incorrect so you should use another AC adapter

This is a middle pin issue, you will find the laptop doesn't charge either but will power the unit, if the power is connected, the laptop will hang and use reserve resources, if you unplug it, the machines performance will dramatically increase.

replace your power adaptor and all will be fine, i have had the same issue.

How about this step, try to turn off the laptop itself. Remove the cables and battery just like what you did before, then press and hold the power button for 10 seconds. Then, reinsert the cables and battery on the laptop and then turn on the computer itself. If the laptop restarts, shuts down or freezes with the AC power cables, two things that you should seriously consider. It might be the power cable itself, AC cable port or the circuitry going to the motherboard. And since you have cleaned out the fan and heat sink, you have isolated that problem. Have you plug-in another power cable on your laptop? If yes, then check if it works. Otherwise, the main issue is that the AC port is loose or the circuitry of AC adapter going to the motherboard is not not working. You can re-open the unit and check the circuitry from the AC port going to the motherboard. You may check the circuitry from AC port to the power supply if it is ok. If symptom persist, please contact your local dealer...

I don`t know.