Try another AC adapter to eliminate yours as the problem.
That was the first thing I tried. I also tried the adaptor from the faulty laptop on another Toshiba Laptop to verify it works ok.
Did you remove CPU when measuring? They can measure very low on power rail. Also very strange about capacitor on CPU power causing reboot because of the AC adapter. It should not mater at all and if there is a short, it should not work from any power at all because power goes from the same step down converter anyway. There might be a fault somewhere between step down converter and AC adapter. There likely is some schematic with mosfets which switches step down converter power between battery and adapter.
Yes, the CPU was removed. This seems to be a common fault on laptops that use this particular capacitor. It usually starts to show problems after about three years according to my research.
Is there a handshake requirement with the power supply, I know that many Dell laptops have this and I have had this problem with one in the past, the only easy fix was a new power supply.
No, the power supply is pretty much a 19V brick. the charging smarts are in the battery. the battery communicates with the laptop via an I2C bus.
Had similar problem with a laptop.
it was the proadliser cap under the cpu that goes faulty.
The laptop will charge fine, and will run fine on battery,
but if as soon as you plug in the psu, it will bsod or switch off.
very frustrating having to go to standby mode, let it charge, unplug the psu, start it up, work until the battery is flat, and then repeat. Apparently the cap smooths the power rails, and wnen it fails, the psu injects tOo much noise into the rail.
changing the cap will fix it.
Some people replace that one cap with several smaller value smd caps in paralell.
Re the low readings. Your dmm probably tests resistance at about 2v, which is enough to start some of the semiconductors on the rail conducting, which is why it will show low resistance.
p
Exactly what this one was doing, it was driving my niece crazy.
I read something about the CPU speeding up when the power supply is connected and this is too much for a failing bypass capacitor, causing the BSOD and shutdown. Some of the other suggestions such as lowering the CPU speed and running the laptop in low power mode or shutting down 1 core bear this out.
I'm intending to replace it with 4 330uf 2.5V tantalum caps.
I measured the probe voltage of the dmm I was using at 1 Volt.
why surprised? 0.6 ohm at 1V is below 2watt
btw how did you remove this cap? did you remove the correct one? big black flat square?
this cap is not easy to desolder, usually takes a LOT of heat
That was 0.6 Ohm across the Laptop power rails. I started my electronic training when we used a few hundred volts on the power rails and the most of the time the active components glowed a dull red.
The solid state stuff that came in later brought that down to 12 or so volts and then 5 as TTL made its entrance.
I'm not used to devices that can be powered up by the measuring equipment.
How did I remove it? Hit it with hot air to soften the plastic and then pulled it apart piece by piece.
you need another ~1000uF capacitor in that spot
I'm going the 4 x 330uf tantalum route.
There should be a photo of the cap in question attached to this if I've done it correctly.