Help me find a short on laptop mainboard - Page 1
Forum section: electronics / repair

author: naujoks
author_rank: Regular Contributor
timestamp: December 13, 2024, 06:12:38 pm
content: I have a VAIO Pro 13, which has a short on its mainboard.I measured the short across some capacitors and an indcutors, both on the front and back of the board.I just got a thermal imaging camera and I've been trying to find the short by injecting voltage (1V, 0.5A) on the board.I put the negative of the PSU on a common ground and the positive on the shorted cap and inductor, but nothing got hot at all. In fact, nothing even got warm.Did I do something wrong? This is the first time I'm trying to do this, so it's quite possible I made a mistake.

author: kripton2035
author_rank: Super Contributor
timestamp: December 13, 2024, 06:23:53 pm
content: build yourself a shorty with display (link in my signature)it's an invaluable tool to find shorts anywhere on pcb.look at the videos on how to use it.

author: naujoks
author_rank: Regular Contributor
timestamp: December 13, 2024, 06:40:39 pm
content: That looks like a fun tool, but I would like to try using the tools I have at my disposal already, particularly since I just got the thermal imaging camera.I'd very much appreciate any help with my current problem. I've attached picture of the board for reference.

author: StrayElectrons
author_rank: Contributor
timestamp: December 13, 2024, 07:10:04 pm
content: Normal to have very low impedance due to CPU & GPU section of the processor around power inductors for the processor. Which components you are measuring as short?Secondly, you can buy used motherboard for not so much money and reactivate the windows and keep data.Usually the motherboard has a COA key burned into the firmware serial so no need to pay for key again.Cheers,

author: naujoks
author_rank: Regular Contributor
timestamp: December 13, 2024, 07:15:07 pm
content: I measured a short across one of the bigger black caps and the inductor next to it. Also on some of the very small caps on the back.I know it's a short that's not supposed to be there because I have a similar laptop on which the said components do no measure as a short.Replacement mainboards of this laptop are rare and more expensive than getting a complete laptop (around 120 pounds).I would like to repair this mainboard.

author: Harry_22
author_rank: Frequent Contributor
timestamp: December 13, 2024, 09:08:57 pm
content: Termo imager is the best short finder but you have to adapt to it.It's like a third eye for an engineer. It allows you to find faults in one, two, three.My thermal imager paid for itself in a weeks.Let you see the picture. The capacitor has 4mA leakage at 12V.The termal imager fixes 50mW here.Most likely a Mosfet with good heat dissipation has shorted on your board. You need to add a little more current and wait for some time to heat up the problem area.

author: naujoks
author_rank: Regular Contributor
timestamp: December 14, 2024, 07:15:16 am
content: By how much should I up the amps?I am injecting the voltage at the right place, am I not? I'm injecting it at the cap where I'm measuring the short. Presumably it doesn't matter on which side of the cap I'm injecting?

author: RoGeorge
author_rank: Super Contributor
timestamp: December 14, 2024, 11:04:46 am
content: Usually the short circuit is caused by the small 0.1u or so on the power supply lines, the MLCC type. They are many in parallel sprinkled all over the board. A schematic will help you identify which one is where much faster.Many boards have 0 ohm jumpers/bridges (shown in the schematic) that can be cut in order to isolate various section of the power traces.Either you push a lot of current from an external source (but limit the voltage), then follow the voltage drop until you find the shorted MLCC, or use a short detector, something like thishttps://hackaday.io/project/3635-shorty-short-circuit-finderMy go to is external power supply + DMM (mine has 1uV resolution, though it doesn't have to be that small). When more than 1 MLCC are in parallel close to each other, you just desolder them all and see if the short goes away. If you have the schematic, simply desoldering each of the MLCC on the given power bar might be faster.A good ESR meter, or a milliohm-meter might work, too, by measuring each MLCC on the given power bar and find which one has the lowest resistance.Other method I've seen (but didn't try), is to cover the PCB area with a thin layer of isopropyl alcohol, and the component that heats the most is supposed to evaporate the alcohol faster, so you watch wich component dries first.

author: naujoks
author_rank: Regular Contributor
timestamp: December 14, 2024, 11:15:15 am
content: Ok, but I have a thermal imageging camera, so I won't need to cover theb oard in IPA.The schematic is not available.Even if I build myself a Shorty, measuring hundreds of caps is not very appealing. It's also very difficult to tell where the traces are going, as this is a multilayered board.The voltage injection method works for Northwest Repair and Electronics Repair School ever so often. Shouldn't it work for me?

author: RoGeorge
author_rank: Super Contributor
timestamp: December 14, 2024, 11:35:25 am
content: Quote from: naujoks on December 14, 2024, 11:15:15 amNot sure what the voltage injection method, but I guess it's current injection. That's the method I'm usually using.Take a lab power supply, set it to constant current (mine can give only 3A, so I start with 1A, and increase the current only if I can not distinguish the short circuit). Make sure you apply the correct polarity to the board, and make sure you limit the voltage (from the power supply settings) such that there is no danger for the board. Start with 0.5V max, and see if you can spot anything. Whatever you do, don't set it to more than the nominal voltage on the power bar where you inject the current.Never used a thermal camera, so I have no idea if they can spot such small temperature difference. Usually I've seen thermal cameras used to detect defective ICs or transistors, because those are heating many degrees above the rest, but not MLCC capacitors. The MLCC are very small, and coupled to thick GND plane, which make them dissipate the extra heat very fast. No idea if thermal camera can sense such small temperature differences.It's not trivial to find a shorted capacitor, it's one of the nastiest things to identify. A schematic will help a lot. Without the schematic, you may accidentally measure a coil and think it's a short, and so on.I've searched for "VAIO Pro 13 schematic" and found a lot of results, why are you saying it is not available?https://duckduckgo.com/?t=ffab&q=VAIO+Pro+13+schematic&ia=web

author: Fraser
author_rank: Super Contributor
timestamp: December 14, 2024, 01:48:57 pm
content: I recommend that you view some of Sorin’s repair videos where he uses a thermal camera to identify shorted components…. There are many such videos on his channel !https://youtube.com/@electronicsrepairschool?si=NLJ-2PS4l8qY4MtDNorthridgeFIX also uses thermal imaging for finding shorted components.https://youtube.com/@northridgefix?si=LJjuOpvxMleZ3YUsBasically a thermal imaging camera can easily identify the areas of a PCB that become hot due to a shorted component. You need to apply a low stimulation voltage of around 1V with a constant current limit of around 1A to 3A, depending upon the situation. Be warned that some lab power supplies do not like working into a short and disconnect their output so little to no current flows in the PCB. Sorin talks about this in one of his videos on buying a power supply. The original power adapter of a laptop will often go into protection mode if a short is present so do not use that to power the laptop. With a constant current of 1A present on a PCB, any shorted component on that power rail will normally reveal itself on the thermal camera. Make sure that you apply the stimulation voltage to the power rail of interest after any LDO or DC-DC converter if they are not part of the investigation. Some heavy duty components, such as large MOSFETs can dissipate a lot of heat to the PCB ground plane so more current may be needed to reveal shorts within these components.You have not stated which thermal imaging device you are using. If it is one of the very inexpensive very low resolution types from China you may find it more challenging to locate the failed component. Anything of decent quality with a true physical resolution of more than 80x60 pixels will work for PCB inspection but 256x192 physical pixels, or more, is a better tool for the job.Thermal imaging cameras have revolutionised the laptop and mobile phone repair industries with respect to quickly tracking down shorted components on PCB’s. It is the time that they save the tech that makes them so desirable in a commercial setting. In terms of cost for a thermal camera…. We have never had it so good ! Well done for wanting to learn about this technology in the PCB repair environment. You may wish to research add-on inexpensive ZnSe close-up lenses, both DIY and commercial, on this forum.If you watch a good few of the videos that Sorin has produced, you will learn a lot about common faults on laptops and the use of the thermal camera where a short or very low impedance is present on a power supply rail.The dedicated thermal imaging area of this forum is a good place to ask any thermal imaging related questions that you may have and for information on making a close-up lens etc.Fraser

author: naujoks
author_rank: Regular Contributor
timestamp: December 14, 2024, 03:12:29 pm
content: But I've already mentioned that I've done all those things!I have watched countless Nothridge Fix and Electronics Repair School videos, in particular the ones with voltage injection and thermal camera.My camera is not a cheap one, it has 240x240 pixel resolution and detects low temperature ranges really well, from the looks of it.The search results provided do not actually link directly to the PRO 13 schematics. Sorin and Mo hardly ever have schematics available for their work either.I've increased the amps limit to 1A on the PSU now (remaining at 1V), but still not a single thing gets warm. I checked that the PSU doesn't go into protection mode by connecting my MM to it, and it shows 1V output.The board pulls a maximum of 500mA anyway, so increasing the A limit to 1A wouldn't make a difference anyway.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 14, 2024, 03:36:35 pm
content: If the board only draws 0.5A with the PSU set for 1V and 1A max, then it sees the board+connection wires as a0.5ohmdoh, 2 ohms, not 0.5, sorry. Which means there might be no short at all. The shorted capacitors usually have a lower resistance than 500 milliohm.If by "board is in short" you mean the DMM beeps on the continuity range, that is not a relevant test. The DMM beeps usually at any R under 200 ohms or so, depending on the DMM type.1. - Where exactly on the Vaio board did you measure a short circuit? Mark the points on the previous picture.2. - How do you measure? (what instrument are you using and what settings)3. - Where exactly on the Vaio board did you connect the wires from the 1A/1V PSU? Put a picture of the board with wires.4. - What voltage do you measure with the 1V/1A source on? Measure V at the board side, not at the PSU side (some wires, for example ready made banana+alligator Chinese wires might be made out of iron instead of copper, so most of the voltage from the PSU will drop on the wires, that might explain why the short-circuit can not draw more than 500mA).

author: RoGeorge
author_rank: Super Contributor
timestamp: December 14, 2024, 03:40:24 pm
content: This guy wrote the schematic can be downloaded for free, the message is from a week ago, so I expect the link is still valid:https://www.diy-laptoprepair.com/forum/Sony-Vaio-Pro-PRO-13-repair-guide-schematics.htmlHave you tried completing the download puzzle, as it is wrote in the second post there?

author: naujoks
author_rank: Regular Contributor
timestamp: December 14, 2024, 03:47:08 pm
content: That schematic download link is a scam. You have to sign up to places with your credit card. No.

author: naujoks
author_rank: Regular Contributor
timestamp: December 14, 2024, 03:50:55 pm
content: In some places the short measures just 2 ohm.I also confirmed that it's a short on this board by measuring the same components on the board of the working VAIO, where no short is measured.I'm using a standard digital MM.I'm measuring the short on the coil 3R3 and the cap to the right of it, also on on the big 330uF cap to the left of the CPU, as well as some of the smaller caps on the back of the PCB.

author: RoGeorge
author_rank: Super Contributor
timestamp: December 14, 2024, 04:21:21 pm
content: Quote from: naujoks on December 14, 2024, 03:47:08 pmThey didn't say about credit cards. In that case, maybe ask one of the guys that already downloaded the schematic (from the diy-laptoprepair forum) to share with you what they've already downloaded.As for the 2 ohms, don't know what to say. The MLCC type of capacitors I was suspecting usually go dead short, a fraction of the ohm, not 2 ohms. 2 ohms might be caused by something else. I'm not sure what to advice farther.Maybe increase the voltage to 1.5 or 2V, in the hope that a bigger voltage will give a bigger test current, and that will heat the shorted component more, so to spot it with the thermal camera.

author: Harry_22
author_rank: Frequent Contributor
timestamp: December 14, 2024, 05:16:31 pm
content: Could you connect the good mainboard to the laptop and make some photos via termal imager.

author: naujoks
author_rank: Regular Contributor
timestamp: December 14, 2024, 05:20:32 pm
content: What would the purpose of that be?

author: Harry_22
author_rank: Frequent Contributor
timestamp: December 14, 2024, 05:28:09 pm
content: I like looking at pictures more than reading long texts.

author: eurgenca
author_rank: Regular Contributor
timestamp: December 15, 2024, 09:07:24 am
content: Good one, Harry.

author: Harry_22
author_rank: Frequent Contributor
timestamp: December 15, 2024, 07:49:09 pm
content: Probably you have a short inside the processor that is why it is difficult to see the hot point by thermal imager.