Tbh I'm not really expecting any solutions other than "replace the mainboard" but I'll ask anyway in case someone has fixed the same problem...
Short version:
Toshiba P30-144 laptop. Mostly this thing behaves dead with no lights. Very occasionally the AC power and charge lights come on and then it will switch on and boot normally only to shut down after a few seconds and then play dead again. DC socket is fine, both CPU fans work and the heatsink has been cleaned.
More details:
From what I can see it seems to be going into some sort of protection mode,in this condition the 19v supply is present on the DC jack and up to what looks like the main voltage mosfet controller (can't read the numbers on it) but no volts on the mosfets themselves. (there are 4 of these which together provide 5v - separate from the CPU vcore ones) There is what seems to be a 3.3v standby voltage but no other secondary supplies function and the charge voltage to the battery is 1.4v. What makes me think it's a protection problem is because as the dc adapter voltage is removed there is a brief spike on the charge voltage up to 15v and the secondary supplies come up very briefly.
Things I have checked by substitution - another known working CPU, memory, backup battery and ac adapter. I've also checked all the fuses and simple diodes, as well as the main mosfets. The supply caps are those nasty smd cans that give problems elsewhere but they check ok and I've tried replacing them anyway more in hope over expectation :)
Given that I can't read the id on the main PWM controller, the age of this thing and that any factory level diagnostics is definitely BER any other ideas? ;) :)