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CPU is dead, did my PSU kill it???

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November 5, 2008 12:21:26 PM

I had an ASUS P4s800 with a P4 3.0E GHz prescott.

Recently I took a air compressor and blew highly compressed air all over it to get dust out. After plugging it back up, it didn't work. Initially it turned on for about 1 minute, no screen output, then turned itself off. I turned it on again, and it did the same thing - made a funny burning smell. Then it wouldn't turn on at all. When you hit the power switch, the cpu fan shook a little bit, but nothing happened - no fans, drives, etc.

So I tested the psu by shorting the pins and probing with a voltmeter. Everything looked ok, but I didn't test the ATX12V 4 pin connector. I swapped in another CPU, no difference. If i disconnected the ATX12V 4 pin connector, the the computer turns on and the CPU fan spins (no cpu power so it doesn't do anything of course). But when I pluged this connector back in, nothing happened. So I determined that the mobo was bad, an ordered an refurbed p4s800 off eBay.

Anyway, I got the new mobo and installed it with my old CPU and PSU, and when I turned it on, the fans spun, but no HD spinning or screen output. I tried a brand new PSU on it - same deal. So I figured my PSU must have been bad and blew up my old mobo, and when I plugged it into my new mobo, it blew it up too! So as a last resort, I swapped in another socket 478 processor (older P4 2.6 GHz), and it worked!! Keep in mind that I only tested it with my new PSU from the new system, not the original PSU in case that PSU was bad, I didn't want to toast another CPU!

So, obviously my CPU is dead. How did it get killed is my question? I don't see how blowing air on everything killed both my CPU and my original mobo. Maybe I forgot to plug the CPU fan in the first time and the CPU overheated in a minute and took the mobo out with it, and that was the smell I smelled? More likely to me is that I damaged the PSU when I blew the air inside of it, and it toasted everything. But that doesn't explain why it didn't toast the new mobo when I hooked it up to it. Maybe the dead CPU was preventing the PSU from delivering enough voltage to toast the mobo? Either way, I am afraid to plug my old PSU into my new mobo.

What I'm going to do is order another p4 prescott 478 off eBay (the fastest I can find). But my question is, do I also need to get a new PSU, because I don't want to have to buy another if I don't have to, but I don't want to end up toasting another mobo and cpu! Is there any way to know for sure that my current PSU is 100% safe and not going to toast everything? I mean, if I probe all the pins and they regsiter the correct voltage, is it good to go, or does that not guarantee that there won't be a current spike? Could I just take it to a computer shop and have them hook it up to a PSU tester, or are those not reliable?

I could RMA the PSU if I have too, but I don't want to wait if it's not necessary!

Thanks for your ideas guys!

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November 5, 2008 12:39:43 PM

Air compressor + PC parts = bad, bad thing to do.
The highly compressed air, besides the fact that it probably had a lot of moisture in it, could have physically damaged delicate parts.
November 5, 2008 1:21:55 PM

Should I replace my CPU with a prescott or northwood? The dang prescott always ran at 79C and was slow as balls. I like to run FSX, so I'm going to get either a 3.2 or 3.4 model.
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November 5, 2008 1:36:30 PM

you may have forced dust into the socket, when cleaning dust, you should vacuum, not blow it all over the place where it will settle again later..

If you plan on holding onto that PC, get a Pentium D with a decent cooler..

On the otherhand.. for about 170 bucks you can grab a nice AM2 or LGA775 processor and 2/4GB of DDR2 800 ram off newegg..
November 5, 2008 1:43:46 PM

The Northwoods generaly run much cooler...the one Prescott that was an exception was the SL8K4, 3.4 GHz, 1 MB L2 cache with HT (the non ee model)which was the very last stepping (G1) for that chip and carried a TDP of only 89W and a TS of 69.1 degrees C. Good luck finding one though.

Otherwise, try to find a gently used 3.2 Northy - you are more likely to find one of these.

Good luck
November 5, 2008 1:48:14 PM

Thanks, I got a 3.2 SL6WG Northwood off eBay for $35.

I already built a new system with a quad core intel after this happened, but I want to restore this computer system to use as a server and multimedia PC.

Now, my question is if I need to get another PSU or not! I am afraid to try my old PSU on my new mobo CPU. Although, it apparently didn't damage it when i plugged it into my new mobo with my old CPU (although it didn't work).

I still don't know the point of failure in my old system and that scares me!
November 5, 2008 1:52:12 PM

Kohlhagen said:
you may have forced dust into the socket, when cleaning dust, you should vacuum, not blow it all over the place where it will settle again later..

If you plan on holding onto that PC, get a Pentium D with a decent cooler..

On the otherhand.. for about 170 bucks you can grab a nice AM2 or LGA775 processor and 2/4GB of DDR2 800 ram off newegg..



My socket is a 478. Also, when I was cleaning with the air compressor, the processor was never removed from its socket. I don't like the idea of vacuuming a PC do to the incredible force a vacuum could have. It could suck some caps right off the mobo.

I'm still thinking I damaged the psu when I put the nozzle in the fan slot in it to blow the dust out the other end.

The only thing I have yet to do is test the old psu on a known good system, and that's something I'm afraid to do! How do I know for sure that my PSU is good without risking anything?
November 5, 2008 2:07:22 PM

Many older power supples (those before ATX specification 2.0) did not have sufficient overvolt protection and would fry MBs causing a cascading chain of destruction that would also take out the cpu, or fry the chip directly. The sad truth is that many of the newer "cheap" power supplies don't either. Also, bad caps on a MB can also take out a cpu. In your case, I suspect the old PS was the culprit. The one thing to never cheap out on is the PS, and even good ones over time, will drop below spec and eventually crater the MB or the cpu.
November 5, 2008 8:02:32 PM

sidespar said:
This is the PSU I had:

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

I paid $40 and it was less than a year old. Does this qualify as an el-cheapo supply? Would it have overvolt protection?

RMA it or is there anyway to test it?


I would RMA that puppy and then sell the replacement on eBay! You have to be careful testing a PS, because at low load, they'll often pass muster, only to fail when they reach higher output demand. You can get static testers at the egg for cheap, but they don't tell you what's happening at higher loads. You would need to put the PS under load and test with a multimeter to find out for sure.

And yepper...one clue is the length of the warranty - only one year! Also, the 'el cheapo' will usually make some outlandish claim somewhere it the advertisement...in this case, 100,000 hours mtbf. What they usually don't tell you, is the operating temperature at that rating...which is usually 25 degrees C, which if you do much gaming means an actual mbtf of much less because it'll kick up to 50 degrees C or more. I try to stay with Corsair power supplies which offer a lot of bang for the buck, come with 5-year warranties, and are rated at 40 or 50 degrees C. I've bought 5 Corsairs, four 520s, and a 650 for my personal use, and have never had a problem with any of them. The Antec Earthwatts series seem to offer a lot of stability for the price as well, as do a few models from PC Power & C. On all my new builds for customers, I try to stay with Corsair or Antec EW.
June 24, 2009 3:48:35 PM

Most likely your PSU is OK and you damaged some components on the mobo using the high speed air. It can generate very high voltages along its path due to electrostatic induction, and that can definitely damage some chips. The faster the air, the worse it can be. If there is dust or lint, it is worse yet.
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