Laptop motherboard troubleshooting - Page 1
Forum section: electronics / general

author: brainwash
author_rank: Frequent Contributor
timestamp: March 01, 2013, 11:42:44 pm
content: I bought a cheap broken laptop from ebay to try my hand on. Some might consider it cheating, but I'm calling to your experiences in possible diagnosis, I've been working on it for the last 15 minutes and I might try do something irreparable.Symptoms: upon pressing the power button the fan spins for about two seconds and then it shuts down. No video output (LCD, VGA, S-Video), no response on the keyboard (numlock for example), no beeps. Southbridge chip gets very hot to touch (~80 degrees Celsius).Power indicator remains lit, battery charging indicator shows function as expected. The only way to shut it down is to keep power pressed for 4 seconds, then the southbridge starts to cool, power indicator is off, battery indicator remains lit (as normal).Basic specs, as far as I can make out: it's based on Turion 64, Southbridge NF-430-N-A3, graphics card some nVidia chip (code G6150).It looks very clean inside, someone had tried to take it apart but I think they gave up midway because some parts were never removed.I checked for voltages around various places and I get 5V, 3.3V, 1.2V. I don't think I ever saw a 12V anywhere, only 19V.I will check some more but it's a rebranded laptop and I cannot find even basic specs, even on the official website. Just the usual 'no user serviceable parts inside', 'do not take apart' blabla.I'm thinking this thing overheated and the solder balls ruptured. So my idea is to try a reflow of the graphics chip and maybe the south-bridge. That is, place several layers of aluminium foil with a cut-out for the chip and use the heat gun.Edit: it was advertised as 'display stopped working', there are no signs of water damage, no obvious visual errors. I assume there is no  short since nothing else gets hot and the supply voltages are constant. I'm testing it with only the supply plug connected, RAM and CPU and a VGA cable connected to the output.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 02, 2013, 12:37:15 am
content: Just a small update, I sprayed cool air on most of the stuff to see how it reacts but I haven't seen any change. I also wasn't able to find any 12V line.Possible laptop using very similar configuration: HP Pavilion TX1000

author: amyk
author_rank: Super Contributor
timestamp: March 02, 2013, 05:53:57 am
content: There are probably model numbers on the mobo, which you can use to find the OEM model. For example the HP Pavilion TX1000 is a Quanta TT8. You can use the OEM model to search for schematics and other info. TheTT8(schematic in link for reference) has no 12V rail either, because no components on it need that voltage.The nVidia 6150 sounds familiar, it might be one of those flawed chipsets that could be temporarily fixed by reballing, but would eventually fail. The southbridge shouldn't be getting to that temperature so quickly; if it had a heatsink you should not run it without.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 02, 2013, 11:00:24 am
content: Thermal design is really crappy, the GPU shares the same heatsink with the CPU but through a thick (~8mm) blue thermal pad. The southbridge is not cooled at all, just bare chip.I will try reflowing (not reballing) the GPU and afterwards improving the cooling on those parts.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 02, 2013, 11:37:22 am
content: Yep, the GPU was the cause. I did a quick reflow with the profile like this: 0-260C in ~90 seconds, 260C for about 60 seconds, rampdown at ~ -6C/s. I wanted to keep it longer at the peak but the cardboard shield was starting to catch fire.I just put the power button cable and the supply cable and the laptop made it at least until bootscreen.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 02, 2013, 11:50:35 am
content: Just a quick question to your BGA experts out there: is the chip "floating" on the balls or is it flush with the board?I saw that some people put copper pennies between the heatsink and the chip and was wondering if with rising temperatures and continuous pressure the balls would get squished and short each other. There are some springs for pressure relief but I don't really know how this stuff works.

author: Kilroy
author_rank: Regular Contributor
timestamp: March 02, 2013, 06:13:17 pm
content: The BGA sits off the planar on the solder grid.I flood Kester 979 no clean liquid solder flux under the BGA to thoroughly clean and prep the grid array, follow that with oceans of 99% isopropyl and blow pressurized air all around underneath. Repeat several times. Lots of liquid flux, lots of isopropyl, lots of air, and liquid flux again just prior to the re-flow procedure. You want the grid array as clean as you can...clean, clean, clean...cleaner even. Impossible to over emphasize the importance of cleanliness if you want the re-flow to "take" well.I don't use any shielding....never seen the need unless you are using hurricane force air flows and shotgun sized nozzles. I use very low airflow through a very focused nozzle. You should be able to blast small SMD chips and have them stay in place. If they don't, there is way too much cfm at the nozzle. 3-4 cfm is loads and loads of airflow if you have the heat...and that is not much air...common tools I have tried won't even go that low.Preheating the planar is always a good idea.Don't use copper pennies to improve heat sinking contact....they are not going to wick heat properly...surface is too uneven. Use flat copper stock that at least matches the smoothness of the die on the chip and use good quality compound to mate the surfaces. A little downward pressure from the heat sink is fine...any more is not necessary or helpful. Too much pressure may actually squish the shim out of place, and you should always check to make sure this has not happened, in any event, before you close things up.

author: amyk
author_rank: Super Contributor
timestamp: March 03, 2013, 01:57:30 pm
content: Quote from: Kilroy on March 02, 2013, 06:13:17 pmAlso note that the silicon die is quite brittle and uneven load may fracture it. A small amount of thermal paste can help even the load on the die as well as fill in surface imperfections. The die surface is very smooth.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 03, 2013, 02:08:07 pm
content: Great advice so far.Quote from: Kilroy on March 02, 2013, 06:13:17 pmI used a household heat gun/paint stripper, I don't have a reflow station.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 06, 2013, 10:51:55 pm
content: First laptop is running pretty fast with XP and Lubuntu, I never saw the GPU temperature sensor reporting above 75 degrees. I just used a piece of sheet metal and some thermal paste to replace the thermal 'foam'.I just picked up the second laptop today, but this one is a little bit underpowered, I bought it mainly for parts and XP licence.While probing around I think I found at least the issue why it's not powering. The PF1 component pictured below is probably a polyfuse (5A) and does not conduct at all. Next to it is PL2 which I don't know exactly what it is but it has zero resistance so I assume it is a fuse or inductor. Then is the piece DALE R025F which I thought was a fuse but it is actually a current sense resistance (0.025 ohms).Anyway, this was just for future reference in case some beginners want to tackle projects like this.What worries me is shown in the second picture: Q20, Q18 and the 0 ohm resistor. I don't know if it's a hack job at the factory or something happened to them. The yellow thing there is a piece of something like painter's tape. There's also that green wire which I assume is a production 'feature'.Oh yeah, model is some obsolete Fujitsu Amilo based on Pentium M and running with SDRAM and PATA harddrive, neither of which I have at hand, so this one goes probably in the parts bin.

author: AlfBaz
author_rank: Super Contributor
timestamp: March 07, 2013, 12:02:15 am
content: Just skimmed through this post, not clear as to wether you have the schematic. If not you may have some luck herehttp://www.edaboard.com/thread210455.html

author: amyk
author_rank: Super Contributor
timestamp: March 07, 2013, 07:59:35 am
content: That mod on the VGA connector maybe DDC related (possibly for use with a projector). It's most likely not factory-original, as they would use kapton tape instead.

author: Psi
author_rank: Super Contributor
timestamp: March 07, 2013, 10:01:12 am
content: Quote from: brainwash on March 03, 2013, 02:08:07 pmYou can use those kind of heat guns to reflow if you're really careful.Just keep in mind that its the equivalent of using a belt-sander to clean your teeth.Those paint stripping heatguns have the power to turn your PCB into a large black pile of charcoal if you get too close on max setting.

author: brainwash
author_rank: Frequent Contributor
timestamp: March 07, 2013, 07:34:59 pm
content: Well, I did test it on some stuff to find out the sweet spot and was able to desolder and resolder 64 pin packages on some test boards. I think on the low speed is pretty close to how a real station works. The only inconvenient is the airflow is a bit on the high side and the nozzle big, so you either attach the shrinking attachment and get a bigger airflow or just make sure to stay away from heat sensitive stuff. I highly recommend it to people who don't do much SMD rework stuff, because you can use it around the house as well. You anyway need to monitor the working surface with an IR thermometer or the K-probe on your multimeter.Third and final laptop arrived today. Unfortunately this one works properly. Fortunately there is some intermittent contact at the DC jack, so I had the chance to take it apart. I don't think I've ever seen full size RAM in a laptop until now. It's probably the first generation of mobile AMD (Athlon XP-M 3000+) platforms and it has better performance than a typical netbook. Battery life was probably abysmal.Just in case anyone wonders, I payed 25E for the first laptop (no HDD, no cdrom), 20E for the second (no charger, no HDD, no RAM), 10E for the third (no HDD, no battery).

author: Alana
author_rank: Frequent Contributor
timestamp: March 07, 2013, 10:28:34 pm
content: I have el-cheapo hot air rework station and i would like to try to learn how to reflow laptops. Have at least 4 that may be workable after reflow/rebaling. Any tips or tutorial how?

author: brainwash
author_rank: Frequent Contributor
timestamp: March 07, 2013, 10:33:29 pm
content: 1. See the post from Kilroy, above, it has almost everything you need to know.2. You can read this long thread:http://forum.gsmhosting.com/vbb/f404/nvidia-gpu-chip-problem-746159/3. Experiment! Use boards that have little value but are still working, take off the chip, clean and reball or try to reflow. Youtube has a lot of reballing videos. Stress the boards afterwards to see how long they last.

author: amyk
author_rank: Super Contributor
timestamp: March 08, 2013, 07:02:41 am
content: Quote from: brainwash on March 07, 2013, 07:34:59 pmThat looks like a Uniwill 755CIx. There's a schematic floating around on the Internet.

author: Psi
author_rank: Super Contributor
timestamp: March 08, 2013, 07:14:50 am
content: Quote from: Alana on March 07, 2013, 10:28:34 pm-You need quite a bit of heat to reflow laptop CPU/GPU's because they're so large.-It can take quite a while to get them up to temperature without risking thermal shock.-Get lots of liquid flux under the chip before starting.-I recommend having a temp sensor mounted under the board near the chip your trying to reflow so you have some idea how hot it is.-A PCB preheater is really useful if you have one.It's quite common to reflow a laptop/ps3 BGA and fix the fault, but have the fault returns a few weeks/months later.You can't see the BGA joints so its very hard to get flux under it and also to know when the reflow has finished.

author: Kilroy
author_rank: Regular Contributor
timestamp: March 09, 2013, 06:04:35 am
content: The best way to tell when the solder grid is molten is by *very* gently nudging the BGA with a non-conductive probe as you heat the die surface. When the grid array reaches re-flow temperature a little prod with a birch wood "orange stick" will slightly displace the die on the solder grid, and as long as you don't jab it too aggressively the die will easily re-align itself with no problem. All that is necessary is that you know when you have achieved a molten solder condition across the entire area of the grid array. Once that has been confirmed you should remove the heat, just as you would with any soldering procedure, and allow the planar cool.Re-flowing solder is never the ideal, but that being said I have seen good re-flows last significantly longer than the time elapsed before the original failure so there is usually little to lose by attempting it.

author: img
author_rank: Regular Contributor
timestamp: March 10, 2013, 05:25:49 pm
content: If you are doing BGA reflows commercially, they are the type of repair that'll spoil your reputation. You can be lucky a few times and the reflow will work for a while, but this is not a reliable repair. A reliable repair of a laptop that died of GPU overheating is a reball and an upgrade of the cooling system.That said, if you have a dead laptop and not sure if the cause is just the GPU, then a quick reflow can show if the patient comes to life, after which you reball and fix the problem long term.Whether a reflow or a reball, preheater is definitely your best friend.