Component heating up

[lezsimply]

Good day guys. I'm a little bit lost as of this moment I got and old Fujitsu Amilo laptop with a heating component. Motherboard has power but does not boot. Found IC U31 very hot after pressing power button.

Please check attachment. As you can see I got voltage on all PINS. I notice pin no 8 is very high. and pins 3 and 4 are low. I already replace ic with same value. I laso removed c904 which I thought was faulty but same thing. Need to know if which pin is causing IC to heat up. thanks to all.

[mariushm]

Re: Component heating up

That's a linear regulator:

It works by dissipating the difference between input voltage and output voltage as heat, so it's natural that it would get warm.
It could get hot if there's a component after the chip that uses a lot of current or a component that's faulty and causes a short circuit, forcing the linear regulator to output up to its maximum capability.
Get a multimeter and check capacitors for shorts after the linear regulator, or maybe whatever is connected to that 1.05v VS is dead.
If there's a short, it's not uncommong to see the regulator overloaded and showing a much lower output voltage than the confgured one, which seems to be the case here.

[stj]

Re: Component heating up

one of the 4 output caps could be bad - or something it feeds not on that diagram.
before you solder anythnig, repeat the test without the cpu & ram etc - just incase

[lezsimply]

Re: Component heating up

Thanks for the input. I forgot to mention that I found short on output rail. I already removed C281 and C358. C243 and C371 are empty. Short still there, don't know where +1.05vs goes after. I'm looking at Q45 as the output of +1.05vs. But not so sure. I attach schematic diagram. Thanks again for the help.

[rookieme]

Re: Component heating up

In order to find the short you have to supply the power rail with external power supply at 1V.
The short will heat up and you're able to track it and remove the heated part.

[lezsimply]

Re: Component heating up

no lab psu for now. Does this have something to do with low reading on R785 and R786? Both have 37k ohms on my meter. Different from what is indicated on schematic. thanks again.