What an odd fix. 2500$ laptop killed by an 0603 ceramic capacitor. - Page 1
Forum section: electronics / general

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: August 12, 2016, 07:49:57 pm
content: 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.

author: Kjelt
author_rank: Super Contributor
timestamp: August 12, 2016, 10:16:33 pm
content: Very nice work, what did your new boss have to say ?

author: Vgkid
author_rank: Super Contributor
timestamp: August 12, 2016, 10:20:09 pm
content: Thanks for this post. Will need to keep this in mind, when I buy my next laptop.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: August 12, 2016, 10:33:22 pm
content: Quote from: Kjelt on August 12, 2016, 10:16:33 pmThey were impressed. I might have more tasks like this in the future if something comes up.

author: blacksheeplogic
author_rank: Frequent Contributor
timestamp: August 12, 2016, 11:39:38 pm
content: Quote from: iamdarkyoshi on August 12, 2016, 07:49:57 pmItis notthe cost of the parts (when obtainable) that often determines if a device is repaired or replace.

author: iamdarkyoshi
author_rank: Frequent Contributor
timestamp: August 13, 2016, 01:14:17 am
content: Quote from: blacksheeplogic on August 12, 2016, 11:39:38 pmIts whether you can find the damn issue in the first place, and how much it costs to pay someone to do so. I enjoyed this fault hunt though

author: whalphen
author_rank: Regular Contributor
timestamp: August 13, 2016, 03:22:25 am
content: Nice story. And good job!

author: German_EE
author_rank: Super Contributor
timestamp: August 13, 2016, 09:12:27 am
content: This is where the new thermal cameras are useful, your shorted capacitor would show up as a bright white dot.

author: Brumby
author_rank: Unknown
timestamp: August 13, 2016, 11:51:47 am
content: Quote from: German_EE on August 13, 2016, 09:12:27 amSomething I've always wanted to be able to do.But every time I start looking at thermal cameras, my specifications seem to get affected by capillary action. They start wicking up to a four digit purchase price.

author: David_AVD
author_rank: Super Contributor
timestamp: August 13, 2016, 12:21:18 pm
content: Only the other day I located a short in a SMPS by applying 5V (limited to 10 Amps) across a secondary capacitor (12V rail).No thermal camera, so I used one of the analog sensors on the end of my hand to find the hot spot.Turned out to be a pair of diodes mounted (hidden!) between the switching transformer and PCB.

author: b_force
author_rank: Super Contributor
timestamp: August 13, 2016, 12:30:05 pm
content: Very nice job!!The only thing I am wondering about, and that's more from your boss/company perspective.How much time did you spend on this and how much will you save by just ordering a new motherboard?

author: Richard Crowley
author_rank: Super Contributor
timestamp: August 13, 2016, 12:58:22 pm
content: Quote from: German_EE on August 13, 2016, 09:12:27 amOr use Louis Rossman's technique of swabbing the area with alcohol and observing which component(s) evaporates most quickly. #11 on this list....https://www.eevblog.com/forum/chat/pearls-of-wisdom-from-louis-rossmann-worth-thinking-about/

author: FireFlower
author_rank: Regular Contributor
timestamp: August 13, 2016, 05:25:44 pm
content: Well done, have used same method at work many times. Employer considered thermal camera too expensive and my fingers cheap, so burning fingers seems nice way to find small hot component with instant alert

author: wraper
author_rank: Unknown
timestamp: August 13, 2016, 05:48:55 pm
content: Quote from: FireFlower on August 13, 2016, 05:25:44 pmExcept it is very hard to find one tiny component which is hot among the thousand of others. And impossible to find something that is 5-10oC hotter than it should be. IR camera can pay off in a just few repairs which otherwise would be hopeless, or ridiculously time consuming. IR camera makes finding many faults taking just a few seconds instead of hours.

author: wraper
author_rank: Unknown
timestamp: August 13, 2016, 05:58:46 pm
content: My workflow of repairing hundreds of raspberry Pi which I bought cheap. Check if the micro SD slot is broken (third of the faults found) ->Apply the power -> watch the current, if higher than normal -> IR camera -> another third of the faults found. Just like that I find faulty components on 2/3 of the boards in half a minute per board. They are cheap, so I cannot spend half a day to find some faulty ceramic cap (one particular cap often fails because of mechanical stress because of being close to the edge of the board).

author: mikeselectricstuff
author_rank: Super Contributor
timestamp: August 13, 2016, 06:05:59 pm
content: $200 on a Flir One or Seek would pay for itself in one repair.Anythermal camera is vastly better than none.

author: nctnico
author_rank: Super Contributor
timestamp: August 13, 2016, 10:12:24 pm
content: Quote from: mikeselectricstuff on August 13, 2016, 06:05:59 pmI agree. I recently got a Flir C2 and it has been very helpful already (but the MSX image doesn't work for close-ups). For example: I wanted to track down some current leaking in a circuit which was supposed to be powered down and a 0603 resistor lit up in the image even though the amount of power was minimal (200uW).

author: Psi
author_rank: Super Contributor
timestamp: August 13, 2016, 10:23:23 pm
content: ah, the curse of the shorted ceramic cap, seen that a few times.It's such a problem that in the automotive world (and probably medical/military too) they put 2 ceramic caps in series on main power rails.So if one goes short the device still works.Usually put one 90deg from the other, so any board flex/vibration usually only cracks one of them

author: Alex Eisenhut
author_rank: Super Contributor
timestamp: August 14, 2016, 12:17:41 am
content: Quote from: German_EE on August 13, 2016, 09:12:27 amWhat if you put the board in the freezer for 30 minutes, then take it out and let somecondensationfrost form, then plug it in. Where the condensation disappears first ... it's hotter.

author: Psi
author_rank: Super Contributor
timestamp: August 14, 2016, 01:10:50 am
content: Ya don't need to use the freezer, just hit PCB areas with an air duster can upside down.It will cool the are down and anything hot will be instantly obvious.

author: Kjelt
author_rank: Super Contributor
timestamp: August 14, 2016, 08:39:25 am
content: Yes coolfreeze and follow up in detail with an ir thermometer.But now the thermal cameras are in the reach for hobbieists they are IMO the most appropiate tool for these kinds of faultfinding tasks.

author: batteksystem
author_rank: Regular Contributor
timestamp: August 14, 2016, 03:34:39 pm
content: Quote from: Psi on August 13, 2016, 10:23:23 pmIf the cap short out the power rails how does the device work?

author: David_AVD
author_rank: Super Contributor
timestamp: August 14, 2016, 08:58:17 pm
content: Quote from: batteksystem on August 14, 2016, 03:34:39 pmI've highlighted the important bits above.

author: Messtechniker
author_rank: Frequent Contributor
timestamp: August 14, 2016, 09:41:23 pm
content: In some cases I have been able to initially smell a hot componentand then sense it using the back of my hand or if more adventurouswith the skin potion between upper lip and nose. The latter comes with the riskof a component suddenly blowing up in your face. So be careful.The other day sniffing helped me to identify a 22 uF/35 V electrolytic capacitor I had builtin the wrong way round. Silly me..... simply too tired at the time.I really should get a thermal camera to do troubleshooting with a more professional approach.Yours Messtechniker

author: CJay
author_rank: Super Contributor
timestamp: August 15, 2016, 07:03:06 am
content: All those tips about temeprature testing with fingers are very nice but an ex colleague of mine still has the scars on his fingers from a tantalum capacitor which exploded while he was gripping it between thumb and forefinger so I tend to avoid that where possible.Also, lots of power ICs have thermal shutdown, so cooling them can lead to similar situations occurring, at one SERT lecture I attended the lecturer was quite keen to show off the scar on his face where he had used freezer spray on a frame output IC in a television, it came out of thermal shutdown and promptly de-encapsulated itself rather vigorously, one fragment of epoxy lodged itself half an inch below his eye.I'd quite like a thermal imaging camera.

author: David_AVD
author_rank: Super Contributor
timestamp: August 15, 2016, 09:23:18 pm
content: The FLIR One attachment certainly seems like a reasonably priced option these days.I must admit I didn't realise they were on the market. The last time I looked the cheapest option was still well over $1000.

author: Kjelt
author_rank: Super Contributor
timestamp: August 15, 2016, 09:36:41 pm
content: Dont understand Flir, selling a 160x120 imager for less then 300 but if you want the same resolution for a standalone device you need to shell at least 2600, makes no sense.

author: BradC
author_rank: Super Contributor
timestamp: August 16, 2016, 02:06:09 am
content: Quote from: Psi on August 13, 2016, 10:23:23 pmI've just repaired my Apple Thunderbolt display PSU for the second time. Another shorted MLCC.After doing some deeper reading on MLCC's I'm almost shocked at how fragile they are. After the thermal abuse I gave the remaining ones after my first repair (back in 2013), I'm now not surprised another one failed, and the bigger they are the more sensitive to process variations they seem to be.

author: Brumby
author_rank: Unknown
timestamp: August 16, 2016, 06:38:54 am
content: Quote from: mikeselectricstuff on August 13, 2016, 06:05:59 pmI quite agree .... but often when I look further into a category of equipment and become more familiar with the specifications, features and capabilities, I get drawn into an escalating performance target. Settling for less becomes undesirable and paying for the performance target is unjustifiable.Translation ..... I would go for a working Flir E4 at $200 AUD.Rather unlikely.

author: CJay
author_rank: Super Contributor
timestamp: August 16, 2016, 07:20:16 am
content: Quote from: BradC on August 16, 2016, 02:06:09 amThey're a very common failure, ISTR people selling MLCC kits for laptops because they were so often a cause of failure.