Dead Motherboard, or something else?

Hi all; thanks in advance for any tips and advice you can give.

A while back, my wife spilled a glass of water on her laptop - it was kind of funny, as we were on Skype at the time, she left the room to get a glass of water, and about a second after I heard her re-entering the room there was a Niagara-like cascade of water that appeared on my screen for a second or two before the window went all fuzzy, then black.

My wife did what she could to dry the computer out, to no avail. We replaced the laptop some months back, and because I knew there was no chance of getting it replaced under warranty, I stuck it in a closet. Recently, I got it in my head to try and fix the darn thing myself, but (as I had pretty much expected) I've had no luck.

Symptoms:
- When the power supply plug is inserted in the computer, it turns on without the power button being pressed.
- Several lights come on
- The CPU fan spins for a second or two, then stops
- The hard drive spins audibly.
- There is no display on the monitor, not even a faint one.

Steps taken
- Checked hard drive in another computer; it works.
- Checked RAM modules in another computer; they work.
- Inspected motherboard for faults. There appeared to be some evidence of a short near one of the components (I'm far from expert at identifying SMDs): there was what looked like slight charring.
- Scrubbed the motherboard with a toothbrush and denatured alcohol.
- Booted computer with RAM modules removed. There were no POST beeps.

All of this says to me that the motherboard is fried; is there any possibility that I am wrong?

Thanks very much!

 

Well, if it was only water, then scrubbing with a toothbrush and alcohol was not necessary. In fact, some components are coated with resins to prevent air from corroding the contacts. Not sure what alcohol would do for that long term.

The char mark is a clear sign there was a short and subsequent arc where there should not have been. Unfortunately, evidence of a short (scorching) may be some distance from the device that originally failed or was damaged. Often the short, which causes excess current in the circuit, damages more than one component until one of those components fries, opening the circuit.

Unless you have the service manual (assuming the maker publishes one - many don't) and test equipment, you may be out of luck. If you can see the damaged device, and if you can find an exact replacement, you might be lucky and that might be the only failed device. And then you might able to fix it - assuming you have the necessary tools and soldering skills. Alternatively, you might find a replacement motherboard and swap out the whole thing. Or take it to a shop.

That said, if that notebook is getting old, it may not be worth the time, money or effort if the resulting machine is so slow you want to toss it back in the closet. In that case, you might just pull the drive and stick it in an enclosure to copy off and purge any personal files.

 

Thanks for the reply!

I scrubbed the motherboard because there appeared to be corrosion on some of the solder joints - although the water was drained after the spill, it's possible that some hung around. I also wanted to get rid of the charring (or what appeared to be charring) in case it was causing a short.

If motherboards were populated with through-hole components, I'd break out the trusty soldering iron. Unfortunately, I am not an industrial soldering robot, and so cannot reliably replace SMDs

The computer is relatively new (it's a Lenovo U550). I've scoured the web looking for a replacement, but there's no joy as yet - and Lenovo itself refuses to sell me a replacement. I don't think that this model was particularly popular, so I doubt there's much of a secondhand market. If, however, you happen to know where I might find a replacement, please let me know! Although my wife has a working laptop, I wouldn't mind using the Lenovo as an HTPC - although the computer is nothing special (SU7300 Pentium, onboard Intel GPU, etc.) it does have an HDMI out, and I'm not a resolution freak, so...

Thanks again for your help! I will at least salvage the HD and RAM, and if no motherboard turns up, maybe sell the carcass for a pittance.

 

I hear you. I actually had to take a 16 hour course for soldering on multi-layered circuit boards before being authorized to use our Pace soldering station on such boards. I'm long out of practice now.

You might get a bit more than a pittance for the display, if it still works. Same with the inverter and BL tube. And the CPU itself may still be good. Did you check the power supply? Some have internal fuse or thermal links that blow. The notebooks regulator/charging circuits may too, if you can spot it. Depending on type and how mounted, they can be replaced fairly easily.

 

16 hours, yeesh! I suppose complexity is the price of progress... just seems a shame that someone with decent skills could fix a $1000 guitar amp at home, but not a computer that costs half that...

I've checked the power supply - it's at the right voltage, but for some reason, I can't get a reading of the current - the little LED on the supply cuts out when I touch the multimeter probes to the power supply plug, and the meter shows "0".

I'll see if I can find the fuses and thermal links on the regulator and charging circuits. I know that some current is getting to the motherboard, because an LED at the front of the console comes on when the power supply is inserted, and the circuit leading to the LED has to pass through the motherboard. Whether or not current is getting everywhere it needs to is another matter.

Any tips on how to test the display, inverter, and backlight tube?

 

You measure current in series so that may be your problem.

Yeah, motherboards are almost becoming disposable. Most cost less than $100. It can easily take a trained, well equipped technician a couple hours, using sophisticated (and expensive) test equipment, to troubleshoot down to component to level. A couple hours of labor, plus parts, can easily cost more than a new motherboard. So it is no longer cost effective to fix them.