Finding an electrical short

PC issues...

Wouldn't turn on. Replaced PSU. Turns on for a half second enough to wiggle the case fan and gpu fan, then turns off.

I'm hoping its a crossed wire or easy to fix electrical short. Suggestions of less obvious areas to check?

Other suggestions welcome too.

Is the new PSU the same size or bigger? Board and GPU might be to big of a draw.

If you are using a power strip make sure you are not tripping it (some reset on their own.)

Find someone with a PSU tester and test both units.

Had a psu test on the old one. 12v not working. Assuming, but not tested, other psu is functioning. New and old are the same size.

Tested PC in wall mounts instead of surge protector, no change.

Personal suspicion is CPU fan. In that brief moment that fans wiggle, it doesn't move. Would make sense to prevent starting if CPU fan is faulty.

Ordered some thermal putty in the off chance that I need to remove the cpu/heat sink - putty is better quality that it came with anyway, so worth buying now that I'm doing fixes.

Need to purchase some canned air...

Unplug all components from the motherboard (power supply cord, HDD, ram, etc.) and all components from the power supply.

Plug in only what's needed to run the computer. No extra fans, DVD drive, or any other peripherals you might have. Try it now.

If it doesn't work try this:

Turn the power supply switch off. Unplug it from the wall for a minute. Plug the power supply back in and flip the switch on the power supply but do not turn on your computer just yet. Wait two minutes! I'll explain below.

Now turn on your computer. If it works, great. If not, keep reading.

I had a computer that did exactly the same thing and sometimes needed 10 tries before it would turn on. It still worked fine, so I basically never turned it off. Hibernate or sleep mode only.

MB have capacitors on them and if they are failing they won't charge and store power properly. As long as they stay charged you should be ok. It's when you turn off the computer the charge runs down.

Since you changed your PSU and you're still having problems, that's my next best guess.

Let me know if it works.

Weird...

Tried the above with no changes. Non-essential things, I included the power leads to the motherboard (24pin power connector and 4 pin atx power conector), the psu, and the CPU fan. Graphics are in-built, so I detached the dedicated card. Same issue.

On a whim I tried it without the 4pin atx power connector. The computer powered up.

Astonished, I turned it all off, re-assembled and tried again with everything attached except the 4pin atx power connector. Again, all powered up.

That said, CPU doesn't seem to be running. No bios and can't get a monitor to work (tried both dedicated hdmi and in-built vga on different working monitors).

So...either the 4pin connector male (psu), the 4pin connector female (motherboard), or the processor itself is faulty.

Still, this is all-around good news. Don't have to replace the graphics card and the other connections seem to be fine.

Suggestions?

Okay, some internet research. Seems this isn't a unique issue. Idea is that the mobo is functioning everywhere except in the connector that powers the processor.

Looks like solution is one of two things. Either 4p atx 12v connection is faulty on the psu end, or the entire mobo needs replacing just for that faulty component.

Solution is pretty simple, I go back to the PC store. Check the psu there. If faulty I return it to them. If it works, I get to purchase a new mobo.

When looking for a short, the easiest way to find on on a power rail, is to identify a ground pin, and connect one connection from a multimeter to that, then after that, use the other test lead from the multimeter to measure the resistance of each power rail. if you suddenly see an extremely low resistance, then you have a short on that rail.

Many motherboards have a large number of layers, (you may even get stuck with an 6+ layer board, so repairing a short that is not caused by a passive component failing to ground, will be extremely hard. depending on the power, you may have to grab a thermal camera to spot the short, feed some noise into the rail and then get an oscilloscope and probably a fluxgate magnetometer in order to probe some of the underlying layers of the board for where the noise crosses over the strongest, and then using some really tiny rotery tools, excavate that part of the board until you reach the damage, and then fix it, then rebuild the layers using some low viscosity non conductive epoxy and conductive material to repair the traces.

though in this case, that will be an insanely difficult task which is why it is rarely if ever done on modern equipment, it is more popular for electronics from the 70's and 80's where PCB layouts were not as dense, and traces were larger. (on a modern motherboard, you are likely to see many traces which are fractions of a millimeter wide, and even worst, many data handling traces are length matched, and if you have to dig through one, the odds of repair are insanely low.

if you have a warranty on the board, then just RMA it. (easiest solution)

Issue seems common enough for msi boards like mine. Just not common enough to address the issue on the msi site.

Anyway, went to PC shop, got a replacement after confirming it wasn't the psu. Without further issue, PC should be running as soon as I can get home.

Thanks for the help.

Grrr...still not working. Getting close to cutting my losses....

do you have a wood table or any other non conductive surface (please to not use the antistatic bag)?

at this point i recommending running the system outside of the case, connect just the mare minimum components needed to get to the Power supply, motherboard, CPU, GPU, and RAM

In some situations a damaged or warped case will cause the motherboard to flex, in in some cases, some motherboard layouts will have sockets far from the mounting holes, and thus some people may install the motherboard into the case, and then go with installing items like the RAM and heatsink, and during that process, the board will flex as they push it, and eventually end up lifting a solder pad due to the board flexing at an area where a surface mount component is located.

(PS it is also possible to get 2 bad components in a row)

Sorta solved it.....

Realized that my old PC had working components in the areas that new PC seems to be lacking in. Sure enough old and new work together, even the old mobo fits in the new case. Issue is that processor is the old one, so no planetside 2 anytime soon. Still, I'm happy to have a PC again.


So, old mobo, ram and processor, new case, fans, and hard disk. The purchased psu came in handy too. I'll have to return the replacement mobo. I am a bit curious how long this one will last, given than I'm running 64 bit win 8 on a mobo and processor that was running vista with the old hard disk.

Old issues in summary: Wouldn't power on at all until PSU was replaced. Then it wouldn't power on unless 4pin 12v atx power connector was unpluged. Replaced mobo and would turn on, but no video at all (not a monitor fault) and didn't fully boot. Chances are high ram was/is faulty or incompatible with the replacement mobo. I'm at my financial limit already. I'd consider another purchase if certain that it would be the last, but at this point, pattern dictates that once I get the next bit fixed, a new issue will arise.

Reminds me of the children's book stone soup. A con-man convinces a family to make him soup by insisting that a stone can be made tasty if they just add one more ingredient. Ultimately, man with a rock convinces frugal family to make him soup... with this PC project, high odds that I'll have replaced every component before PC is fixed. I feel like I'm building a PC the hard way, rather than repairing one.

Lol....looks like old processor meets system requirements for planet side 2....

Will need graphics from the new PC and more ram, but could theoretically run PS2. Very amusing. I may have been over ambitious in replacing the old PC...

WOW! I need to recover from my nerdgasm.

"When looking for a short, the easiest way to find on on a power rail, is to identify a ground pin, and connect one connection from a multimeter to that, then after that, use the other test lead from the multimeter to measure the resistance of each power rail. if you suddenly see an extremely low resistance, then you have a short on that rail.

Many motherboards have a large number of layers, (you may even get stuck with an 6+ layer board, so repairing a short that is not caused by a passive component failing to ground, will be extremely hard. depending on the power, you may have to grab a thermal camera to spot the short, feed some noise into the rail and then get an oscilloscope and probably a fluxgate magnetometer in order to probe some of the underlying layers of the board for where the noise crosses over the strongest, and then using some really tiny rotery tools, excavate that part of the board until you reach the damage, and then fix it, then rebuild the layers using some low viscosity non conductive epoxy and conductive material to repair the traces.

though in this case, that will be an insanely difficult task which is why it is rarely if ever done on modern equipment, it is more popular for electronics from the 70's and 80's where PCB layouts were not as dense, and traces were larger. (on a modern motherboard, you are likely to see many traces which are fractions of a millimeter wide, and even worst, many data handling traces are length matched, and if you have to dig through one, the odds of repair are insanely low.

if you have a warranty on the board, then just RMA it. (easiest solution)" AOD_Mokona512