I did the same what 999thay did with external fan and unplugged build in fan. Laptop all day on with no shutdown.
I noticed also with startup during posts "1 AMD Northbridge rev unknown". What could be the problem???
Have you found the problem.
I am working around the same problem and did the same with the external fan.
I am thinking of problem with powersupply of build in fan. I have unplugged build in fan during testing with external...