Repair / Toshiba C850-1G3 Satellite Motherboard / Short Circuit

[xan]

Hi everyone,

i need support to try repair Toshiba C850-1G3 Satellite Motherboard  i can hear typical click of a short circuit when i plug power cord and i just measure voltage internally from the plug to the motherboard and it's ok 19 v but not power up... what's next ? the sound seems come from the area around RAM... could you provide some schematics?

  thank's!

[xan]

Guys i got the schematics... are this the right for my motherboard ? could you help read it and suggest something to try... ?

https://drive.google.com/file/d/0BwtsySw9QknfVHdXajlBWjRLSFE/view

thank's again

[LateLesley]

As a suggestion, why not try and find each of the power rails mentioned on page 4, and do a ohms test on them. I'm sure one with a hard short would stand out. Then you can look at what's on that rail, and check all the caps on the rail. It seems to be common for caps to die, even surface mount ones.

But the first step is to find the dead rail. It could be confirmed with measuring the voltage too while trying to power on. The non dead rails will try and lift the voltage, the shorted rail won't, unless its a chip that's away, and not a cap.

[xan]

mmm i am too newmbie to understand completley what you suggest... for now i did (before i read your message) some voltages reads on main line these are the results... do you think the mosfet on left side is gone ? and maybe something else?  could you provide step by step procedure ?

[xan]

Hi again! i just made few measurement and i'm bit sure to desolder and replace IC FDMC8884 could you check on schematics if i am on the right way guys ? waiting before start desolder!!

Thank's

[coromonadalix]

I think the brown Q lettered smt part is a fuse, un less it is an power resistor in a current limiting circuit ?

check it before removing any parts, you may have another one ...


On the other photo near the mini pci card, the white smt is a fuse for sure, check it too

[xan]

The Fuse Marked with Q it's working, voltage it's ok about 19,42 volt, and on the white fuse near pci (in front of battery connector i got 1,02 volt) i think on this last one i have no correct voltage cause of IC FDMC8884 fail.. but i still not sure.. what's next ? thank's for support.

[Zucca]

i just made few measurement and i'm bit sure to desolder and replace IC FDMC8884 could you check on schematics if i am on the right way guys ?

You should upload your measures on the schematics, like this newmbie did:

[xan]

Thank's Zucca! i'm really newbie... i understand only some little part of the diagram block... so i think i have exactly this situation... i made the measurements again like this guy...

https://www.ifixit.com/Guide/How+to+Repair+Tohsiba+Satellite+C850+Motherboard+No+Power+or+No+Charge+%28MOSFET+Change%29/107007

If you think you need more specific i will do measurements to help you understand.. before solder and desolder....

[xan]

Some news... bad or not ? ...After resolder a new IC FDMC8884 laptop turn on! but without pressing the power button.. just simply plugging the power cord...    what inspect from here ? maybe some bad soldering on IC cause this kind of issue ?? and what are the correct voltage for battery pinout ??

[Zucca]

Is it reproducible? Everytime you plug in the cable the Laptop turns on? Maybe the button it stucked down?

[Zucca]

i understand only some little part of the diagram block...

Ask what you don't understand in the diagram. Make detailed posts with measures and pictures.
Right now I have the feeling you are trying to fix stuff by replacing componets which may not be bad.

[xan]

Here are some photo after resolder IC i don't have 19.4v just a measurements near 19 v. But it turn on like i say before... Notebook now power on only on power button i change the broken cable and button too, like Zucca suggest (taken from another one)! Tnx!! I'm now inspetting chargin battery... it's stops at 94.4% and without battery i have 3v on big white fuse instead of 1v before resoldering IC. Seems all it's working... Zucca how can i test IC that i removed to be sure it was fail ?? can you teach me ?

https://datasheet.octopart.com/FDMC8884-Fairchild-datasheet-5360054.pdf

[xan]

Anyway guys thanks for support! Ot was not short... but IC failure....just another answer... i would like to undestand how this IC could be broken so what's was the cause of this. Manufacture or overvoltage / overcurrent ??

[Zucca]

how this IC could be broken so what's was the cause of this. Manufacture or overvoltage / overcurrent ??

Normally when the problem is solved, I look at the bad components on the bench and ask the same questions.
5 sec later:"Whatever..." and move on.

Don't know what it was, but if it doesn't happen again... let it go and disappear in the universe noise.