What an odd repair. $2,500 laptop killed by a tiny ceramic capacitor.

[iamdarkyoshi]

Dell precision M6800. A customer brought one into my work (laptop repair store)

The company would normally have just bought a new motherboard, but they are NOT cheap for this thing.

Considering I was recently employed there, I asked if I could take a stab at repairing the motherboard rather than having a new board come in.

The issue is that it was completely dead. Plugging in a charger caused the charger to shut off. I figured there must be a short somewhere.

 

 

First day, I took my soldering station, a 40 year old multimeter, and some soldering supplies, such as flux, solder, and solder wick. Soldering station is a 3 in 1 hakklone.

Found two shorted P channel mosfets, right on the power input. 

This part switches between the PSU and battery for powering the notebook, which explains why the fully charged battery wouldnt power it on either.

 

 

Replaced it with a bodgefet, and the bodgefet died. I traced the path of current, and somewhere, there was a short still, which is why the input fet popped when it connected the 12A PSU to a dead short. Looked and probed all over, couldnt find anything. Tried feeding my 3 in 1 soldering station's derpy bench supply into the input circuitry (after the fets), trying to find where current was going, but it can only muster 1A. Didnt find anything.

 

 

Next day, I also brought my 300W 5A bench supply. Tried the same thing as before, but at 0.5v 5A. After a little bit of letting 2.5w dissipate somewhere, I found the culprit: An 0603 ceramic capacitor, way far off from the switching circuitry. It was smokin hot!

Under the CPU backplate, between the tantalum caps and the upside down 1 2 3 4 white boxes on the silkscreen.

 

 

So I desoldered that cap, replaced it with another one from a piece of ewaste, and replaced the two mosfets with some from mouser.

I originally thought only one was bad because only one measured a dead short, but it turns out that both mosfets were bad. Good thing we bought two.

Lesson of the story: The fault could be anywhere! I would have never thought that a cap on the other side of the board is what killed this expensive notebook, but it was.

Less than 2$ worth of parts, and it runs flawlessly now, and handled aida64 for 20 min, both plugged in and on battery.
 

[TheRedViper]

Dell would have charged him 2000$ for the repair

[glitchmaster0001]

wow amazing how just one little cap can kill an entire board... 

[AresKrieger]

Not uncommon, especially if it's part of the power regulation, fortunately it didn't take anything out with it

[iamdarkyoshi]

12 minutes ago, AresKrieger said:

Not uncommon, especially if it's part of the power regulation, fortunately it didn't take anything out with it

Well, other than some weird p channel mosfets...

[AresKrieger]

23 minutes ago, iamdarkyoshi said:

Well, other than some weird p channel mosfets...

Well yeah, I was more thinking CPU, GPU etc, something pricey, but fair enough

[iamdarkyoshi]

1 minute ago, AresKrieger said:

Well yeah, I was more thinking CPU, GPU etc, something pricey, but fair enough

Yeah a short across a power rail is not nearly as bad as a short in a power regulator circuit

[AresKrieger]

Just now, iamdarkyoshi said:

Yeah a short across a power rail is not nearly as bad as a short in a power regulator circuit

This is very true of course if that happened you would have opened it up, then been like

'Hey boss this laptop is completely fried, needs a new CPU'

 

[Unimportant]

Back when i still had my repair business we used a bench power supply limited to a current that would not damage anything and a infrared camera.

 

Those SMD caps light up like a christmas tree with only a few 100mA when they are shorted out.

 

Nice board level repair, respect, any muppet can swap a board, THIS is repair.

[Curious Pineapple]

My graphics card randomly started causing PSU's to cut off from overload. Left it for a while and just swapped mainboard for one with an iGPU. Got bored of a faulty board so I tried the GPU again, still tripping the supply. I accidentally put it in the slot badly after taking it out to check for anything getting hot and when powered on, it let out a load of smoke and a ceramic cap blew showering sparks out. Been working fine ever since, even overclocked as far as Afterburner will push it.

 

Capacitors are strange creatures, especially when ceramics fail for no reason at all.