Blown capacitors and power supply problems.

July 8, 2005 5:24 PM

My computer is suffering from undervoltage on +5V! Help me out if you are a ninja with hardware.

The +5V line is anywhere from 4.0 to 4.6 as indicated by various sources. The software that was supposed to alert me to this condition wasn't working right. The low voltage wasn't enough for my newer SATA hard drive (which used to work, so this has deteriorated recently) and probably has been the cause of problems for my DVD drive.

I have an Antec 380W power supply and an Asus A7N8X motherboard. Now, I would just go out and get a new power supply, but there is a complicating factor - about 6 caps (on the small side, rated 6.3 volts and a few hundred-thousand uf) on the motherboard are exploded, although they haven't caused any noticeable problems. Could this be causing heightened power draw somehow to the point that the power supply can't maintain 5V or has deteriorated over time?

Caps are way cheaper than power supplies. I've just been way too lazy to replace them, and if it's not going to help I'll continue being lazy and drop the bucks on a PS.

If anyone knows what pins to short to get a modern power supply to power up when its not actually connected to a motherboard, I could probably find out that way as well.

posted by TheOnlyCoolTim to computers & internet (13 comments total)

Uh. Call me crazy, but I'd just drop the cash for new parts. If you're not confident and knowledgeable enough to just go ahead and replace those parts instead of asking for help, it might save you the frustration in the long run.
posted by angry modem at 5:44 PM on July 8, 2005

and by 'those parts', I mean the actual components of your motherboard (and you're braver than I for even considering this venture)
posted by angry modem at 5:45 PM on July 8, 2005

It is probably the bad caps...
posted by Chuckles at 5:54 PM on July 8, 2005

Dude. If you have capacitors exploding, you need to replace your motherboard immediately or you risk detonating the circuit boards for the rest of your components... including any USB devices you have plugged in.

Replace the power supply, motherboard, and anything that you're not confident of (including possibly the SATA drive...).
posted by SpecialK at 6:14 PM on July 8, 2005

Last time I had power-supply-related problems, I just dropped the cash on a good quality unit from PC Power & Cooling and haven't had a problem since.
posted by mrbill at 11:07 PM on July 8, 2005

Connect the powersupply to a friends' computer, or take it to a shop, they will be able to check in two seconds if it's okay or not.

But you are kidding, right? Popped caps on your motherboard and you want to examine your power-supply!? Replace the caps, or better yet, replace the motherboard.
posted by Grensgeval at 4:31 AM on July 9, 2005

Could this be causing heightened power draw somehow to the point that the power supply can't maintain 5V or has deteriorated over time?

Considering that they're part of the 5V or 3.3V power filtering circuit? Oh, yeah (bom bomp.)

Worse, if you've dropped the voltage that low, it means your drawing more current than the PS is rated to output at that voltage. So, you are killing it. If it was a noname, it would have flamed out already, but Antec makes good supplies, and rates them very conservatively (generics would have called that PS a 500W, not a 380W.)

Don't try to replace the caps on the MB unless you're a crazy mad solder jockey -- there's at least four layers in that PCB, probably more. It's trivial to wreak them trying to get enough heat into them to desolder the caps. Plus, you really need to find the right replacements, or they may not survive -- there's more to caps than capacitance.

But that's work. How much is your time worth to you? How much does a motherboard cost? Do the math -- it's almost certainly not worth your time, unless you're unemployed.

BTW, you want to do this quickly -- if those caps start presenting a dead short, it could eat the power supply as well. That could eat everything else. That Antec is being loaded way beyond spec to pull the 5V line down to 4V.
posted by eriko at 7:52 AM on July 9, 2005

The PSU could've popped the caps, I'd be wary of hooking it up to a new motherboard until you've tested the PSU to make sure it's performing within range.
posted by knave at 7:53 AM on July 9, 2005

eriko: Don't try to replace the caps on the MB unless you're a crazy mad solder jockey ... you really need to find the right replacements, or they may not survive
...
How much is your time worth to you?

TheOnlyCoolTim's profile says he is an electrical engineering student. This should be considered a course requirement! Go for it man, break out the soldering iron and get to work!

eriko is right though, you can't just throw any electrolytic cap in those places. I'm quite sure that the 'bad caps' link above talks about the specific ratings you have to look for, if not just google a little and you will find the details.

It is also true that you need to exercise some caution when it comes to testing... Don't put all your best components in the first time you throw the switch... Modern computer components are fairly robust, so don't worry too much.

All this caution and fear, and the whole time-money thing... Man, you people have got to get out more. Well, not so much out actually, you've got to get to your workbenches more. Sure, there comes a time when you have to get on with it and use money instead of skill. Calculating the value of your time the way eriko suggests is for lawyers and accountants.

Don't let these naysayers sap your curiosity TheOnlyCoolTim, or you will have to spend $5 on a new nic 'OneofManyLameTims'... Now that would be a bad time-money optimisation!

Finally, you asked about testing ATX power supplies... That is very simple - google link.
posted by Chuckles at 9:17 AM on July 9, 2005

If you're a whiz with a soldering iron, and have a spare hour or two, you can replace the capacitors. Shouldn't cost more than about $10 for all of them, although you'll find some of them tough to get ahold of. Be sure to replace them with the identical rating (uF) and same/higher voltage rating. Also check the size, you may find the new caps won't fit in the tight spots on your motherboard.

The capacitors will be a bear to remove since most of them will be connected to the ground plane, which will sink all the heat from your iron. You should use a temperature controlled iron, since it will be able to pump out the 50 or more watts you'll need in a controlled manner (DO NOT USE A 50 WATT NON-TEMP CONTROLLED IRON! You'll delaminate the PCB.)

Above all, ensure you respect the polarization of the original caps. Write it down if it isn't silkscreened to the motherboard.

If the correct capacitance rating isn't available, and you MUST substitute, substitute upwards. You should be safe substituting most capacitors up to around 30% more capacitance.

Oh, you only need to replace the capacitors that are same size or larger than the eraser on a #2 pencil. The rest weren't built with that nasty exploding formula.

If you decide to operate the power supply disconnected, you MUST PUT A LOAD ON IT. Connect a hard drive or two to the PSU. Unloaded switching power supplies can immolate.

If the capacitors in the PSU are fried, throw it away. You can hurt yourself replacing them. If you must, you need to replace the PSU capacitors with matching units designed for switching supplies. Don't forget to short out all the old capacitors first before working on them to avoid electric shock.

Enjoy! I know this can be done from personal experience of fixing several motherboards like this.
posted by shepd at 9:32 AM on July 9, 2005

I'd try to fix it first. You can pick up an do a search for A7N8X or A7N8X-X on ebay and you can get some good deals. Or newegg.com has the A7N8X-X for about $60, which is what I just bought. This was the best price I found from a reputable, non-ebay seller.
posted by 6550 at 10:12 AM on July 9, 2005

Just a point, I learned recently that switching power supplies with multiple outputs usually only regulate one output. In most cases this means the 5v is regulated and the 12v floats, but it might be the other way around.

Take a look at the PSU's rated amperage outputs for 5 and 12, and guesstimate your system's total draw on each. If you're drawing way out of proportion (tons of 5 and almost no 12, for instance), you might be confusing the PSU's regulation mechanism.

There's some good detail on this scenario in "The Art of Electronics" which is worth owning and reading anyway.

I'm going to agree with the other posters that your first concern should be getting the magic smoke back into your mobo's power circuits.
posted by Myself at 11:22 AM on July 9, 2005

Thanks for the detailed answers! I learned...

I got my hands on a disused 250 W Enermax PS (seems to be able to power all my stuff at once), hooked it up and got a healthy 5 volts on my voltmeter, the BIOS, and Asus' monitoring software, which apparently only tells you the voltage if it's good. So the immediate problem was the Antec PS, not the capacitors, although it still could be the caps slowly degrading the PS.

I am very lazy and don't like rooting around the enclosed space of a computer case too much, so basically I'm going to just let it rock and roll like this. Soldering caps was a last resort before buying a new motherboard, because I have great big clumsy hands and would definitely break everything. This computer, while in its Frankenstein nature has parts going back 6 years, is mostly almost 2 years old, so if I get a few months to a year out of it like this then I'll be ready to buy a new motherboard and processor. Don't see the point of buying a new A7N8X today.

I could cut some wires and get amp metering on the motherboard, or take the board out and see how the caps electrically present themselves, but as I said, I'm lazy, and looking for the quick minimum of hassle to a working computer which I've found for now.
posted by TheOnlyCoolTim at 4:55 PM on July 9, 2005