How to identify bad cap

[stevenf4i]

Hello, im new so bare with me, please. I have a Asus p4c800 e deluxe MB. all tests have been done trying to find out why it wont boot. i get no post. occasionally it will boot up and stay on for 5 min then shutdown and nothing afterwards. im assuming it has bad caps. nothing on the board looks abnormal. anyone give me a quick idea how i can identify the problem and if their are bad caps how to tell? thanks

[yyonline]

Re: How to identify bad cap

Often times, bad caps will have bulging or domed tops. A really bad capacitor will have dried electrolyte on the top. This looks like a brownish colored substance on the tops. The top of a good capacitor is always flat. However, just because the top is flat does not mean it's good. Some fail without showing it externally.

Get a flashlight and a small mirror. Open up the computer and look for any markings on the capacitors. Report back with what you find, and people on the board can give you some feedback as to what caps may have failed.

[etnietering]

Re: How to identify bad cap

Bad caps will sometimes, but not always, show visual signs. These include but are not limited to bulging/leaking brown or orange electrolyte out of the top, or bulging/leaking electrolyte out of the bottom. There are some brands that are notorious for barfing out all their insides, and some brands generally don't show any outward signs at all. In one of the threads here there are tons of pictures of caps gone bad. Check these out and look at your board again for any similarities. Also, read the manufacturer and series off of them and post that information here, and people will be able to help you.

Also, the board could be fine, and the problem could lie elsewhere. If you don't find anything on the motherboard, or even if you do, check the power supply. There are electrolytic caps in power supplies that often go bad, especially if the power supply is of lower quality. Power supplies can be dangerous, however, so make sure the computer has been unplugged for a long period of time to let the primary side caps discharge themselves. There is lots of info here about both recapping motherboards and power supplies. Post pictures if you can. Good luck!

[kaniki]

Re: How to identify bad cap

also, you could tell what you know or has been done to the PC and your personal experience, like are you good with fixing them or are you new to fixing them.. You say that it will not boot up, but when it does not boot up what happens? Do the lights turn on or is it just that nothing happens and it is like you never touched the button? The reason i say this is if your heatsink has been off the processor and put back on with no new heatsink paste, then maybe your processor overheated and has gone bad.. There are also core components on some motherboards that have heatsinks on them too. Overheating could be a problem. But then again, it could be something simple like needing a new power supply or something came loose (ram, video card, etc).

Another thing to try is pull all the data plugs for the stuff on the motherboard for the things like hard drives, CD ROM's , etc and unplug the power from the back of those devices too and see if the computer still acts the same. It could be something is conflicting with one of those devices. I have seen it happen with both CD-ROM's and hard drives before, but that is not to say that the other devices could not do it too.

[stevenf4i]

Re: How to identify bad cap

thanks so much for the feedback guys. i checked the caps and no visual signs of damage. ill try to get the manufacture of them asap. also i have some computer experience. i don't believe the processor has overheated but i will confirm. i checked the voltages of the power supply and the readings are normal so i can only assume its the caps. thanks for all the info. ill have an update soon.

The cap manufacturer is Rubycon and on the side lists:

6.3 V 1000uf YXG

[yyonline]

Re: How to identify bad cap

Rubycon is a good brand of capacitors, one of the most reliable out there. However, the size and series tells me that this is only one of the kinds of capacitor on the board. The most stressed capacitors on the motherboard are in the VRM circuit, and it would be unusual to find YXG there. As the VRM capacitors are the most stressed, they would be the most likely to fail. That said, it's no unheard of for VRM caps to be okay and have failures elsewhere. The VRM capacitors are usually tall capacitors, often in a row, located near the CPU. If you're having issues, that would be the ones you want to look at most closely.

What is the brand of power supply? I've had power supplies that read okay on voltage, but still wont power a computer reliably.

When it fails to post, are there any beeps? Make sure you have a case speaker hooked up to the speaker leads on the motherboard, if one is not built into the board. If you hear a series of long and short beeps, write down the order (i.e. long, short, long, long), and you can look up that beep code to see what error is preventing it from posting.

[stevenf4i]

Re: How to identify bad cap

thanks for the reply. ive tried multiple power supplies and get nothing. there is no beeps and i do have a speaker connected to the board. i have a multi tester but i have never tested a capacitor and would like to know if this tool would be able to do the job, its called a Fluke 12 Multimeter. thanks