Thinkpad A31p Instant off when external power applied

[cineman]

Hi my thinkpad A31p has recently developed a fault where by it works fine off the battery but as soon as you plug in a powered AC adaptor the laptop goes instantly off. if the ac adaptor is un-powered you can plug it into the laptop and it remains working but as soon as you plug the adaptor into the wall outlet again the laptop goes instantly off. When this happens there is no charging led. If you press the power on button the laptop will briefly start while a powered AC adaptor is plugged in, you can hear the dvd drive and fan spin up but then it goes off. Without the AC adaptor plugged in the laptop will start and run just fine, though the battery has now dropped to 50% charge and there's no way of re-charging it while this fault persists. If you pull the battery and just power the laptop from the mains adaptor again it appears to be totally dead. I checked the AC adaptor and its putting out 16.5V This laptop has given many years of good service and apart from this problem is still working ok. it seems a shame to bin it. Any ideas?

[RealBlackStuff]

Borrow another adapter from a friend/colleague, most Thinkpads up to T43/R52 use the same 72W/16V/4.5A adapter.

[ganon11000]

could be the internal fuse? or the power adapter is on its way out?

[cineman]

could be the internal fuse? or the power adapter is on its way out?

Found the cause of the problem, First I ran PSU into a 4R load to see if it had a problem delivering its rated powerand it maintained 4A ok at 16V so it wasn't PSU problems. I then obtained the Venice schematic diagram to see if i could figure out what would cause the problem. U76 labelled Kozak appeared to be a likley contender as it seems to control all the internal power supplies.

On removal of keyboard before removing top cover i noticed that the cover screw that goes on the left hand side under the keyboard was missing, on further examination it appeared to be trapped between the pcb and the CPU heatsink/fan assembly. removing the screw from this position restored normal operation. With hind site i do remember the laptop rattled if shaken but i thought nothing of it as it had always done this.

Thanks for your suggestions.

[RealBlackStuff]

...the laptop rattled if shaken...

Next time you should try stirring instead!