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#1 |
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![]() You have a laptop that does not power on, powers on but shows no image, crashes, etc… You want to fix it but you don't know where to start.
There are 2 situations:
Sorry, but if you're in situation number 1, we recommend you to use the services of a trustworthy professional repair shop. Unfortunately, if you're not serious about learning, you will waste your time and money, and you will make us waste our time as well. If you are in situation number 2, then please continue and read until the end. This serves both as directions on how to deal with your laptop problems and how to post on this forum. Remember that this is a place for mutual help. It's free as in not paid, so when you ask for something you have to realize people invest their time out of their day for you, without counterpart. And when you help someone else, you do it for free without expecting anything in return. It's also free as in freedom. You are free to ask questions, but people are also free to answer them or not. If you want to help this community, the best way is to learn and help people back when you're confident enough. Tip: if you make effort in your communication and thinking process, people are more likely to want to help. 1. Where to begin 1.1 Identifying the hardware you are dealing with It is very important for you and us to know exactly the machine you are working with and what is inside. 1.1.1 Machine model number Find the full model number of the machine. For example it may be "HP Pavilion 17-f166nf". "HP 17" or "HP Pavilion" is not enough, there are hundreds of laptop that fit this name. If you find multiple model numbers, write them all. 1.1.2 Specifications Find what CPU, GPU, RAM, storage device is actually in the machine. It is not always relevant to the problem, but it helps confirm the parts are compatible or recognize known unreliable parts.
1.1.3 Motherboard model number Motherboard model number is the most useful if you are troubleshooting a motherboard problem. It helps finding pictures, schematics, boardviews, known issues… There is always a number written on the board itself. In some cases there's also a sticker that tells a variant. There are several different board manufacturers, common ones are:
The following manufacturers make their own boards (except maybe a few models here and there):
HannStar don't design boards, they manufacture the PCB. "J MV-4" and "94-V0" are not board model numbers, they are generic markings about PCB characteristics. If unsure, send high-resolution pictures of the board. They are always welcome in any case. 1.2 History, symptoms, state of the machine… Always collect the most information you can about what happened to the machine. What's not working right? When did the problem happen? What was being done with the machine at that moment? Did it start acting up months ago? Was it ever in contact with liquid? Was it ever dropped? Was it repaired in the past already? etc… These give essential hints to where the problem can be. But of course, don't entirely trust what people tell you. Confirm the symptoms for yourself and write them down. Once you identified what's not working as it should, do a visual inspection of the machine. Look for any physical damage (bent, broken, missing stuff) and liquid damage, both on the chassis and the board, and take pictures if there is any. Always make sure the correct AC adapter was used with the machine. Genuine original AC adapter of the correct brand and correct power rating. Even if the connector is correct, it doesn't mean it will work and it can even damage the machine. 1.3 Troubleshooting As a first step you should always disconnect the battery. Also check RTC coin cell battery and perform a clear CMOS. 1.3.1 Parts Always exclude the possibility of a part other than the motherboard being the problem before troubleshooting the board. Swap what you can, disconnect what you can and see if the behaviour changes. Write down your findings. Battery-related issues are 99% of the time the battery itself. Even if the battery is new. There are so many garbage batteries on the market that you sometimes get 2 or even 3 bad batteries in a row. This is especially true for Apple machines. 1.3.2 Board Here we will give just a few pointers to what kind of troubleshooting has to be done if you suspect a board issue. Powers on but no display
No power
When requesting help, please attach a picture of the board with resistance to ground measurements (no AC adapter/battery) and voltage measurements after triggering power button (with AC adapter) on all the large inductors . Powers on, display ok but something is wrong afterwards
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OpenBoardView — https://github.com/OpenBoardView/OpenBoardView Last edited by piernov; 07-05-2022 at 09:57 AM.. |
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#2 |
Super Moderator
Join Date: Jan 2016
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![]() 2. What not to do
2.1. Never reflow large BGA It won't fix the problem since 99% of the time it's not an contact issue between the BGA and the logic board. There's a high risk of damaging the board even further. If you want to confirm if an AMD/NVidia chip is bad, you can heat it up to 200°C max for a minute and a half, no flux. It'll come back to life for a short while and then die again, because it's bad. In this case it has to be replaced. 2.2. Don't suspect that something is shorted with no reason Shorted components are not the only failure mode of a laptop. Additionally, some places will measure low resistance to ground under normal operation. In general, high power low voltage (<2V) power rails will measure less than a few hundred ohms to ground. CPU VCore will measure a few ohms only. GPU VCore with newer NVidia GPU can even measure less than 1 ohm. It's normal. If you suspect a short to ground, always report your exact resistance to ground measurements. 2.3. Never randomly inject voltage Voltage injection is used to find a short to ground. Only consider it after you found that there is a short to ground and after doing a visual inspection trying to find a broken component. 2.4. Never inject 19V If the 19V main power rail is missing, there's a reason, often because a protection kicked in to avoid more damage. For example, the 19V power rail could be shorted to the CPU through a bad high-side MOSFET. In that case, the charging circuit protection kicks in and turns off the DC-in MOSFET. With enough luck, the CPU didn't take too much of a hit yet. If you inject 19V, you are sure to destroy it. Always measure exact resistance to ground to see if there is a possibility of high-side MOSFET short. Always start at 1V and check if any of the large BGA (CPU/GPU/PCH) is warming up. Monitor the power consumption. 2.5. Never randomly replace components If you don't follow a proper troubleshooting process, randomly replacing components will rarely solve the problem and it can create additional issues. 2.6. Never randomly bridge MOSFETs/fuse/components Bridging components can easily lead to the destruction of the board without any way to repair it. If it's a fuse, replace it with a matching fuse. If you don't, it will not be able to protect the board and if the source of the problem is still there, some other component will go up in flames. If it's a MOSFET, its purpose is to stop current from flowing through it when turned off, and allow current to flow through it when turned on. It's not necessarily always turned on, otherwise it wouldn't be there. If it's turned off when it shouldn't be, then there is an issue elsewhere in the circuit, bridging the MOSFET won't solve it. 2.7. Don't apply power to the board with missing components As a general rule, if a component is on the board, it's because it's useful for something. Engineers don't like adding a bunch of useless components on the board, it's harder to draw the schematics and route on the PCB. Some of them can be removed without creating problem if power is applied, but others can kill the board with no possibility of repair. For example, if you remove a buck controller or a MOSFET driver, the MOSFET gates will be floating. They'll charge up enough so that the MOSFET turns on. Of course, you don't want the 19V from the main power rail to go straight through the CPU VCore MOSFET to the CPU. Last edited by piernov; 08-13-2021 at 04:24 PM.. |
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#3 |
Super Moderator
Join Date: Jan 2016
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#4 |
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![]() The ABC of repairing , nice thread.
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#5 |
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![]() Many thanks.
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#6 |
New Member
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![]() Very helpful for less experienced people like me :-)
Thanks |
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#7 |
Badcaps Veteran
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![]() very helpfull
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#8 |
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![]() This is a very condensed guide, many thanks to piernov, your english is excellent for a French!
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#9 |
Badcaps Veteran
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![]() Good Job
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#10 |
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![]() thank you
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#11 |
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![]() Good advices, thank you !
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#12 |
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![]() Very helpful for less experienced people like me..
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#13 |
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![]() Thanks
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#14 |
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![]() thank u so much
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#15 |
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![]() thanks Man
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#16 |
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![]() Good jobe
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#17 |
Badcaps Veteran
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![]() Good Job.. great guide..
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#18 |
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![]() Many thanks for another great write-up Piernov
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#19 |
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![]() Thank you Piernov
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#20 |
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![]() thanks...
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