MSI Desktop board continuity across 3v, 5v and 12v. - Page 1
Forum section: electronics / beginners

author: nerdynerd
author_rank: Newbie
timestamp: February 17, 2024, 07:12:31 pm
content: I'd consider myself atotal n00bwhen it comes to diagnosing electronics, especially something with multiple voltage rails like a desktop motherboard.On a whim I decided to grab some old old boards out of the cupboard and see if some of my more recent knowledge will help me resurect them. Why? i LiKe t0 LeArn.I've run though a few basics and got further then I did the last time I took a stab at this specific board:Board - lol - MSi 990FXA-GD80 MSI Global - The Leading Brand in High-end Gaming & Professional CreationQuestion:How can I trace the component(s) that are causing this. (I have medically diagnosed learning difficulties + ADHD and I'm pretty confident there are some gaps in my self taught knowledge on this subject...)Main observations:1. No POST.2. Board HAS Power.2.1 CPU cooler get > room temp if the fan is off. Once the fan is on, its always warm to the touch.3. Debug LED = "FF" with or without CPU... I say this is for F*cking F*cked, but lets see... Google says it means the board or CPU is F*cking F*cked, so same same but different. I'm not doing this to end it with "FF". I want to learn, irrespective of fixing it "soon".4. Fans spin.5. FAN headers read 10v................................?6. Fan + & - both give continuity to the ground plane ( metal around USB ports).............................?7. All USB2 ports work (charged phone - pulled 5-7v ; used a UNI-T tester aswell.7.1 2x USB3 ports (the only USB 3 ports on the back I/O) are electrically dead - UNI-T tester tool can't power on using the port..........................?7.1.1 I used a butchered phone charging cable and exposed the ends to try test its voltage ( Like political party accountability - there was none) - cant recall is the short was present across those 2 specific contacts, I'll double check. This cable on any ofther USB port on this board gives +-5v.7.1.2 I'll also verify the resistance across those 2 points vs the working USB 2 ports next to it.7.2 A chip just 15mm south of the USB / ethernet ports does get warmer then most other naked SoC/SMD that I can prod with my strong hand (scary movie ref) for 10seconds.8. When the PSU itself is turned on (board itself has not been turned on) 1x LED on the ethernet port lights up and flash's constantly...............................?9. Debug LED's are numerous, I'll upload an image of which ones are lit up, +- 9/10 are, bar 2 for the CPU phase LED indicators (1-8 AFAIR ; 1-6 = lit). Seperatly to the CPU phase LEDS's are (but not limited to) 2x LED's labled "NB", both of these are lit.THOUGHTS:1. Multiple shorts to ground in various erea's of the mobo. (PSU is used regularly).2. Short involves 2x USB 2 ports, ethernet port, cpu's isolated power section on the mobo.3. Perhaps the ethernet / USB 3 port was struck by lightning or a local electrical surge?TOOLS:1. UNI-T UT89x2. " " UT61E3. " " USB Tester UT658Dual4. Soldering iron5. 450W PSU x36. Heatgun7. Aceton / 99% Isopropyl8. DC injector max 60W (12v 6a)

author: Vovk_Z
author_rank: Super Contributor
timestamp: February 17, 2024, 08:08:55 pm
content: I don't see how 3.3, 5 and 12 VDC lines can short together. It can't happen, as I guess.If they are shorted either many chips on a MB is totally dead or PSU won't start (because it monitors it's output voltages).

author: selcuk
author_rank: Frequent Contributor
timestamp: February 17, 2024, 08:29:44 pm
content: I recommend to check the capacitors first if you need to repair old computer main boards or peripherals having electrolytic capacitors. Without supplying power, only visual inspection. If there are bulged or leaked capacitors, they need replacement. If all are good, you can then search for burnt components.