I don't know about acquiring a schematic for trouble shooting the MB, but the first thing I would do is test the power adapter with a load attached. I have repaired several that output the correct voltage but failed to regulate when loaded down.
Also, some Toshiba Satellite computers were notorious for having power connector problems. I trust this computer does NOT have such a problem?
Did you try cleaning the air ducts? When on batter the CPU 'may' be at a reduced clock speed via Toshiba Power Management when on battery. When on the PSU, the CPU will go to full speed and may just be over heating.
There's a second CPU (a little tiny one) that handles the power sequencing. The 'BIOS pages' are only for the big CPU, it's that little battery-monitor one that runs into some kind of trouble, and it has that problem every time the external power is applied and it tries to do the natural thing, run the computer from external power and charge the battery. Somehow it senses overvoltage or overcurrent and shuts down.
Look for small-value current sense resistors that are open, or for semiconductor switches that are shorted (can't turn off). There are often PMOS power switch transistors involved. Also, look for fuses (they might not LOOK like fuses, though).
Battery charge current might be channeled through a switchmode regulator, those have always had problems if a capacitor fails.
My guess is the hard drive is operating on +5v. You could measure it there.
First determine if it has ripple. You can normally take a volt meter set for AC and measure the ripple on a DC bus. Old VOM's used a cap to isolate the AC from the DC component, but the new DVM's generally work for this. If you did find ripple, look for a cap that is bad or possibly a diode that is shorted. First determine if it exists.
(5 pages). Lots of good suggestions some of which include successful repairs. More:
I've seen this twice and fixed it more by accident than by intent. In one case, I left the battery out of the laptop, and no charger plugged in, for about a weekend. When I returned on Monday, everything magically worked normally. In the 2nd case, I was trying various combinations of starting the computer, with the battery, without the battery, with both, etc. At one point, it magically started working. That was about 1-2 years ago, and both customers are still using the laptops.
However, I have another Toshiblah laptop in the office with similar (not identical) problems, that I can't fix. It also won't charge the battery, although it will run on battery if I charge it in another laptop. The problem was traced to a crappy BGA soldering job on the video chip. Try booting from battery in Safe Mode, and then plug in the charger. If that works, then it's probable that you have a video chip soldering problem. (I'm debating the merits of buying an overpriced hot air rework station. I borrowed one, liked it, but had to return it).
Please do not tinker with external power supplies unless you're absolutely sure you're using the correct power plug, and the correct voltage. I've seen what's left of the laptop when the clip leads get swapped, or the power supply mysteriously got to maximum. It's not pretty. The correct power supply is 19v 3.4A negative ground,
Jeff Liebermann email@example.com
150 Felker St #D http://www.LearnByDestroying.com
thanks to your suggestions, I did a BIG step forward, I had a try at this: "In SafeMode Goto control panel--> device manager---> goto processor----> disable one of the two processors --> reboot normally. This FIXED the problem, but 1processor is not really a great fix; more of a work around."
And IT WORKS, pc is now running on external power at the moment, a thing that I've never seen on it. I tryed disabling a cpu core in BIOS in the past unsuccesfully, but disableng from devmgmt.msc fixed it.
I do not think it can be a ripple problem because it did not boot at all when connected on power, but who know? Still have to understand if it is:
- faulty cpu
- faulty cpu power section
- bad cpu/other microcode
I would try to see with scope and multimeter but still don't know exactly what and where to look for.