Did I fry my computer permanently?

July 17, 2005 3:32 AM

Did I fry my computer permanently? [MI]

I'm located in a country with 230V. Someone (alright, I admit it was me) was messing around with the AC input on my computer (desktop, Dell Dimension series). More specifically, there's this little red sliding switch that can switch the input voltage between 230V and 115V. I accidentally switched from 230V to 115V while the power cord was still plugged in. This caused quite a bang and a spark. Fortunately noone got hurt, but now the computer is dead.
Is there something I can do to save it, such as changing the power module? What about the harddrive? Did I exterminate it or would it be possible to salvage at least that? It's not all that important, and if it's too much of a hassle, I might just buy a new one, but if there's an easy way to save it, I might try to.

posted by sour cream to computers & internet (10 comments total)

My idiot younger brother did this a while ago. We just replaced the power supply and it was fine. While there is a chance that the shock will have fried some other electronic component in your system, I reckon trying a new power supply would be a good first move.
posted by chrismear at 3:51 AM on July 17, 2005

Dell power supplies on eBay. I don't believe Dell uses standard ATX power supplies, but it's $20.
posted by effugas at 5:19 AM on July 17, 2005

it's certain that you fried the power supply ... some or all of the rest of your computer may be fried, too ... your hard drive is probably more likely to survive this than other components, but there's no guarantee

once a long time ago, i tried adjusting a sound card with the power on ... the motherboard, chip and ram fried ... the video card, modem and hard drive survived
posted by pyramid termite at 6:03 AM on July 17, 2005

Rumor is (or was) that Dell uses a different power supply than other PCs. I think that the pinout on the motherboard plug is different, I sure some googling will tell for sure.
posted by 445supermag at 7:48 AM on July 17, 2005

I'm pretty sure that adapters are available that will allow one to safely connect a standard PSU to a Dell motherboard.

There's a good chance you simply blew a fuse in your power supply and everything else is okay.
posted by Eamon at 8:57 AM on July 17, 2005

i've done this. just the power supply went. as others have said, dell uses a funny plug.
posted by andrew cooke at 10:00 AM on July 17, 2005

Hmm... Best case is that you have only blown the fuse. However, even if changing the fuse is enough to fix the power supply for now, you may have caused damage that will be noticeable later. Regardless of how the power supply faired, the rest of your computer should be fine.

I have also heard that Dells use special plugs, but I think it depends on the era, so you have to check the specific model and see what comes up in a search (somebody might be able to help there too, but they will need more information than just 'dell dimension').

Just for reference, here is a schematic of a typical ATX supply. No guarantees it is the same of course, I have seen PII era dell power supplies with 60Hz transformers... However, It probably is very much like this schematic in the areas relevant to your problem.



What happened (just exercising my brain here, I might be missing something...):

In 230V mode they run it as a full wave rectifier with two 200V bulk caps in series. In 120V mode they run it as two stacked 1/2 wave rectifiers. So basically, in 120V mode they do a type of voltage doubling. When you supply 230V to the 120V mode you give the capacitors and switches (C5 C6 and Q1 Q2 in the schematic) double the expected voltage, which is bad news for those components.

When you gave the capacitors too much voltage they should have immediately drawn a lot of current, which should have blown the fuse. If the capacitors were able to charge up beyond their specs you may also have overvoltaged Q1 and Q2. This would have caused them to fail short, drawing even more current. Whatever happened, the fuse should have blown very quickly. So, C5 and C6 might be fine, damaged but functional, or failed. Q1 and Q2 are either fine, or failed short.

The output voltages will have blipped up for a moment while this was happening. If C5 C6 and Q1 Q2 were overspecified the output voltages might have gotten quite high (here is a case where putting 'better' parts would have caused more damage). If the output voltages were high enough long enough you may see damage in other parts of the computer - I think this is very unlikely.

Of course there are a few components of secondary importance that might have suffered during the event too... That would be too much detail :P
posted by Chuckles at 10:33 AM on July 17, 2005

I agree with everyone else: it's unlikely that more than the power supply was damaged. It's probably more than just a blown fuse, though replacing the fuse might be worth a try. Was the bang accompanied by any smoke or unpleasant smells? If so, I'd skip straight to replacing the power supply module.
posted by hattifattener at 11:39 AM on July 17, 2005

One of my "technicians" did this once. He then "repaired" the power supply by soldering the fuse holder together and then plugged the computer back in without changing the power supply switch or rectifying the voltage. I happened to walk in as he was testing and was greeted by a flame about a foot long shooting out the back of the computer. The computer "worked" even after this with a new power supply, although it had some problems.

I recommend backing up everything as soon as you can get the system working again. I would even recommend backing up the data from your hard disk using another computer before you do any testing with this one. Good luck.
posted by Yorrick at 12:10 PM on July 17, 2005

On the chance that you will still catch this -
I'd recommend getting a replacement power supply that is modified for dell towers. the back panel of the psu (what you see when looing at the back of your computer) is different than standard psu's. The extra $10-20 or so is worth it.

I too had a computer damaged, though it was a random power surge that got past my crappy power strip. Lost my ram and semi-crippled my HD. I'd recommend running some diagnostics on your drive and ram when the PSU is replaced just to make sure it doesn't go south on you later.
posted by efalk at 12:21 AM on July 18, 2005