Looking For Some Help To Troubleshoot ATX Motherboards - Page 1
Forum section: electronics / beginners

author: Dragon45801
author_rank: Newbie
timestamp: May 25, 2023, 02:47:42 am
content: Hi all,I am trying to get into electronics repair as a hobby. I have a decent amount of soldering experience and electrical knowledge and bought some broken things to try to repair/learn on. My current project is a Gigabyte Z590 UD AC. It will not do anything, no lights, no signs of life whatsoever and I am trying to figure out where to start. I have not found any good tutorials online for how to identify the various power rails or how exactly the power header initiates the process to reach post. I would like to learn how to test mosfets, et cet. I understand how to test fuses and resistors and maybe capacitors. Any help/tips would be appreciated on where to even start looking. Thanks.

author: u666sa
author_rank: Frequent Contributor
timestamp: May 25, 2023, 11:06:44 am
content: Generally, mobos and video cards don't bring you money. Cell phones, in particular iPhone, not so much Samsung, and definitely not cheap samsung, bring good money. Tablets, again Apple. Laptops, Apple and others do also bring good money. Other things like video cards, and motherboards, that's time (and money) wasted. Because, think about it, you have a business, you renting an office, each hour has a particular price, you have to meet this requirement, otherwise you spending money. That said, you bought the mobo for yourself to have fun with it. I hope it was cheap -- price of such thing in broken condition is about 500 rubles, or under 10 U.S. bucks, and often time you can pick entire working systems for about the same money. In fact two weeks ago or so I picked up LGA 755 system with 27 inch dell monitor, all working, after some tender love and care, first I chased down low 3.3 volts in power supply, then realized I'm repairing working power supply, 3.3 has to be loaded to give full voltage. It happens.Then mobo was not booting, resetting BIOS properly with battery out and jumpers shorted, it started. Monitor needs a flex cable, from one side there are vertical lines. I paid 1500 rubles for system block and monitor, I'll be using it instead of my laptop for boardview and schematics, more space on my desk. When the ad come up, I did not ask questions about the condition, didn't even asked if it was working or not. Based on the pics, I assumed it was all working. After a while of fixing things you become a good psychologist and can judge problems remotely.This would be my approach to this mobo. Obviously you need CPU and RAM installed.Your motherboard has CMOS battery. In no power-on condition, first thing you do is take out the battery. On old mobos these batteries can often have no power and even be shorted out. Now, supposedly, taking out battery should reset your BIOS? Right? Wrong! Experience shows that taking out battery often has no effect on BIOS defaults. You read that correctly. How is that possible? I do not know nor care nor try to comprehend. So even though my A+ cert class instructed me to either take out the battery or short clear CMOS jumpers, the proper instruction istake out the battery AND short clear CMOS jumper. Clear CMOS jumper should be somewhere around that battery. With battery out, using that jumper, clear the BIOS. Try to start it.You need a good modern POST card. With POST card inserted see what you getting.Let's assume no POST whatsoever.At this point you take the mobo in your hands, and use very good light, and magnifying glass, and look visually all over the mobo for signs of burned and/or liquid damage. Use your nose, smell it all over the place. Your mobo is black, it might be hard to see, but make sure to do a good visual inspection. In fact, this step might be good to do first, but I bet you did some sort of visual inspection before you bought it, and if not before you bought it, then at least when you received it. If you find water damage, clean it with some**c2-80/120 and toothbrush, then depending on condition, use some flux and soldering iron to make things nice and shiny. If it's burned (highly unlikely, really) replace and check circuit.**Benzine is sold in hardware stores, use it, it is same as flux off.Let's assume there was no water damage and nothing was burned.At this point you get out your programmer and stick a proper BIOS bin into your BIOS chip and try to fire it up.In 99% of the time your mobo should work at this point.That remaining 1% does not bring money. I haven't been down that road with mobos. But on laptops you see if you can get boardview and schematics. If you can not get boardview and schematics, you let it go. Of course, there are some people who have the ability to get to the bottom of an issue without schematics and boardview, but they usually do it as a hobby, no money is involved, and if money is involved it is just symbolic.These things are a pandora's box if you get down this far. Sure, if you lucky it is some mosfet, you replace it and it works. You might also be lucky on some really old board and replace caps and it works. But really when things go down to where you have to replace chipsets, that's problematic. Mainly because they are expensive and can not be returned, and there is no guarantee that the chip your receive is working or will be working trouble free in the future. So any practical mobo repair comes down to smelling it, looking at it, wiping down water damage, resetting BIOS, programming in new BIOS, checking mosfets and caps, including any ceramic caps.

author: u666sa
author_rank: Frequent Contributor
timestamp: May 25, 2023, 12:43:09 pm
content: Speaking of the devil.Begin signing up to different forums and repair groups. Often times you need boardviews and schematics and the way to get them is to be a member, that means having points with different cummunities, if you want them for free. Usually you provide advice and get points, that's how it usually works. Not all boardviews and schematics get be gotten for free, not all the time.Here is boardview and schematics for your board, via 1 day trial, download as many as you can while on there, different once, grab whatever.https://vk.com/wall-186715629?offset=780Then you can delete your account and register again and repeat this procedure when needed.

author: MathWizard
author_rank: Super Contributor
timestamp: May 26, 2023, 11:35:57 am
content: Have a look at BadCaps forum, there's quite a few boardview layout schematics, of older mobo's anyways.I don't know much about mobo's, but they usually have 1 main chip, like a 128-pin MCU/uP, called a super I/O. That's like a mini computer on the mobo. It does the basic startup rountine's, and a bunch of other stuff too.1st it needs 5Vstby power from the PSU, if that's good, and you hit the PWR button, it signals the PSU to fully startup. Then various power rails on the mobo start up, and secondary rails, like for power to the RAM.Along the way, pretty much all the chips controlling voltage rails, will send out a power-good signal, if everything is fine, and sometimes that signal lets the next section of the mobo, just with a few logic gates and a pass-Mosfet, to power up.Have a look at this SuperI/O chip datasheet. I have a broken motherboard, and I ruled out a few things, but gave up or now. Just trying to solder wires around and onto the superI/O was a bit of a nightmare.Hope for a simple chip failure, or power section failure.It's larger than 4MB, so I can't post it, look upNCT6796D_Super IO datasheet,as an example of a mobo controller chip. There's a little bit in there on the startup power sequence.Besides looking for power-up issues, I'd be lost.

author: Dragon45801
author_rank: Newbie
timestamp: May 26, 2023, 10:18:42 pm
content: Wow thanks for of the info! Really, really appreciated. I am just trying to improve my soldering skills and dabble a bit in electronics engineering. I work in IT during the day so this is all just for fun to see if I can fix stuff. I got the board for about $30 bucks. If I can fix it I'll just keep and use it. I think I have determined that I have no 3.3 standby voltage and that is why it does nothing whatsoever. Again, thanks for the help.

author: MathWizard
author_rank: Super Contributor
timestamp: May 31, 2023, 10:39:16 pm
content: So do you have an oscilloscope ? That's really what you'd want to monitor each rail on startup, to see if they actually start for a moment and then get told to shutdown for some reason. There's a lot of caps that could fail on these, and they just can't maintain the correct output rail voltages.Yeah on the mobo I worked on, the 5Vstby came in from the PSU, and that goes hardly anywhere. And then I think there was a buck/step down converter, that made probably 3v3 as a lower Vstby. When the computer is put into sleep mode, the RAM Vrail gets derived from the 5Vstby, not the main 5V rail.So to find the separate step-down converters for the voltage rails, look for their inductors and controller chip very close by. Most the controllers will be just some 8-pin chip. And pretty all of them should have an enable pin, and a pwr-good/pwr-ok pin.RAM runs off 1.8V, and that's 1 of the 1st buck converter to start up. I think on my mobo it was derived from the main 5V rail from the PSU.The main 12V in from the PSU, pretty much only supplied the 2 CPU rails, and 12V power to the PCIe slots.Once the smaller rails get going, there's often a series-pass mosfet, that acts as a switch, controlled by the superI/O, or some little bit of discrete logic, to allow the output voltage/current to go to the right place.