How to measure the failure - Page 1
Forum section: electronics / general

author: Jane
author_rank: Frequent Contributor
timestamp: February 14, 2013, 07:21:41 pm
content: Is there a way how to find out the reason for the failure of a computer mainboard itself? (No POST executed).So, I think 3 reasons are possible1.Faulty CPU2.Faulty BIOS3.Faulty PCBHow( what pins ) to measure to know it is No.1 or No. 2. or No. 3?Thanks

author: SeanB
author_rank: Super Contributor
timestamp: February 14, 2013, 07:32:48 pm
content: Power supply first suspect, then board, ram and CPU.Pull the ram and CPU off, and see if it will respond to the power soft switch to power on and off. That then allows you to check power supply voltages. Replace CPU and ram, clean edge connector on ram and try again. Otherwise you need known good units to swap out. Sadly the more modern CPU units are not as robust as older ones, and they do fail. Older ceramic Intel CPU's almost never fail unless the board melts the pins off.

author: Smokey
author_rank: Super Contributor
timestamp: February 14, 2013, 09:13:48 pm
content: This is my motherboard troubleshooting method. This assumes the power supply is good, which you would need a load of some sort to really test anyway, so unless you have a big load or another known good supply you can swap with and test that way, just assume it's good if the voltages are right.1) If the motherboard is under warranty, send it back and get a replacement. Don't bother looking at it.2) If it's out of warranty, do the following...a) Check for bad caps. If you don't have an ESR meter, just check the big ones to see if they are bulging. If bad caps are found, replace.b) After checking for bad caps, stop messing with it and throw it away. Since it's out of warranty, the whole computer is probably old enough to need to be upgraded anyway, so toss it and buy a whole new machine.If you think about it, even cheap motherboards have all the features that make a PCB really hard to design and work with. Huge number of layers, really fine pitch and BGA components, controlled impedance matched length high frequency traces (we are talking GHz here), and a bunch of components that you can only buy in the 10000s qty even if you could figure out what the part number was. If it's not just a problem with bad caps, and you don't do that stuff for a living, just toss it and get a new computer. You aren't even going to come close to fixing a CPU, or PCB issue. Good luck reflashing the BIOS as well unless that ROM is in a socket, which I don't think they even do anymore do they?

author: Alana
author_rank: Frequent Contributor
timestamp: February 14, 2013, 09:37:34 pm
content: Does it power up?If not - check psu:Disconnect from PC, connect to mains, check if you have +5V stand by on purple wire and if voltage is within specs. I'd recomend to put some load there - like 50ohm resistor to see if voltage sags - if so you have bad cap in your psu - most common type of fault.If its ok then start up main psu - green wire to ground. PSU should start.Check voltages, possibly under load - i use car light blubs as load - 12V 21W on 5V line and 2x 12V 5W on 12V line. Voltages within 5% tolerance = good psu.or swap it with known working one.If it powers up but no POST and no beeping then I'd remove motherboard from case, place it on something insulating, connect buzzer to PC speaker pins if motherboard has not have one and listen to beeping.If it works it should beep because of "no RAM installed". Power down, insert RAM, start up - beeping should change [no VGA installed] or if it has integrated VGA it should boot.With integrated VGA motherboards its often important to have RAM in first slot next to CPU, otherwise integrated VGA does not work.No beeping and no visible faults like bad caps or things alike = motherboard or bios problem.BIOS problem can be resolved with "clear CMOS" jumper, provided that BIOS backup battery is OK - check with meter - anything below 2.9V may cause funky behavior.If that does not solve problem its usually broken motherboard. CPU usually survives but to be sure you need to check it in other motherboard.Rest is swapping components and testing them in compatible working PCs. Be sure to completely power down pc under test before removing or replacing anything - i fried a motherboard because i was not paying attention and removed ram from powered up system. Now i unplug mains cord from PSU to be sure.And with PC stuff its good to clean up connectors, especially on RAM with acetone or nitro solvents. I had few "faults" that were result of dirt, especially nicotine residue clogging up VGA and RAM slots.

author: G7PSK
author_rank: Super Contributor
timestamp: February 14, 2013, 09:53:01 pm
content: You can get cards that plug into a pci slot that will give you a diagnostic. Like this one.http://www.ebay.co.uk/itm/PC-MOTHERBOARD-ANALYZER-DIAGNOSTIC-POST-TEST-CARD-UK-/121016355499?pt=UK_Computing_Other_Computing_Networking&hash=item1c2d230aabThey do not cost very much so well worth having in your tool box.

author: Psi
author_rank: Super Contributor
timestamp: February 14, 2013, 10:05:22 pm
content: First thing to do is inspect the capacitors on the motherboard and powersupply.Bad caps is one of the most likely reasons for failure.

author: haveissues
author_rank: Contributor
timestamp: February 15, 2013, 11:44:07 am
content: If none of the above seems to be faulty I am sometimes successful doing a bios recovery. It usually involves naming the bios something specific, putting it on a usb stick and holding down a key combo when turning it on. If it is a problem with a corrupt bios the system will flash it from the memory stick. The procedure varies greatly with manufactures though and I only try it if I'm board or really interested in reviving that particular board.

author: Rerouter
author_rank: Super Contributor
timestamp: February 15, 2013, 11:55:33 am
content: a few of those suggestions are skipping the basic checks that should be done first...- to start with, disconnect any peripherals that are not required to boot, e.g. hdd's optical drives, sound cards, and video cards if you have an onboard video output,- test to see if it posts (power-on-self-test) will either beep or start showing the bios on your monitor,- check all power connections, most motherboards have a 20+4 pin connector, and a 4/8 pin connector for power, if you have a video card see if it needs a 6 or 8 pin power connector,- then onto power supply, link the green pin to a black with a paperclip and measure for some voltages, just note that some modern ones will not power up this way, so if you see nothing you wont be able to test it unless connected to a motherboard,- if that all check out or cannot be tested, you remove all but 1 ram dimm, and try 1 at a time in different slots, this is more often than not the cause for computers not booting, if it magically springs to life then you have found your culprit,- following that would be cpu and mobo left as the culprit, and neither are easy to eliminate without a matching product to test with,bios is very rare to corrupt, its more than likely a pcb fault will occur before a corruption short of a power failure while flashing, which comes back to mobo vs cpu,hope this helps narrow it down / possible fix it

author: firewalker
author_rank: Super Contributor
timestamp: February 15, 2013, 11:58:42 am
content: Quote from: G7PSK on February 14, 2013, 09:53:01 pmAre those devices really useful? I always thought them to be a "toy".Alexander.

author: Rerouter
author_rank: Super Contributor
timestamp: February 15, 2013, 12:11:45 pm
content: in most cases those diagnostic cards do not come with a listing of what each code refers to, and generally leaves you as stuck as you began with,short of building it for the first time, a computer generally works as normal or fails its post and cycles, if your lucky you can catch the last code it shows before falling over, but in most cases the power cuts at the same time and your left guessing which one it was from the last you saw :?

author: grumpydoc
author_rank: Super Contributor
timestamp: February 15, 2013, 01:12:25 pm
content: QuoteIt's not really possible as there's no standardisation of POST codes.I have one somewhere, I think it's an expresscard format one - never used it