Possible to have a CPU with one bad core?

[ishelly404]

I have a system with an AMD Athilon II X4 640 cpu that has been unstable ever since I got it. Windows would crash randomly and an Ubuntu livecd wouldn't even boot.

After some troubleshooting, I found that the culprit was the cpu, and when I looked in windows task manager, the 4th core was always at about 60%, even when the other cores were idle.

Anyway, I was wondering if disabling the 4th core in the bios would be enough to fix the problem, or is it new cpu time?

[LDSisHere]

Re: Possible to have a CPU with one bad core?

It may not be the CPU, it could be a motherboard problem. Check the mother board for bulged and/or leaking capacitors, if you find some then that may be your problem. I would try and find another system to test the processor in before jumping to conclusions. If you buy a new one and the problem is the motherboard then you have two processors and no motherboard to put them in.

[ishelly404]

Re: Possible to have a CPU with one bad core?

When I checked the motherboard for bad caps, I found that most of them are polymers or Panasonic FJ, but there are a few Chemi-Con KZG caps by the PCI-E slots and the USB ports. None of them appear to be bulging or leaking though. Is it possible for them to go bad after only a year? The system has been on 24/7.

EDIT: I just disabled the 4th core in the BIOS, and the system seems stable.

[ratdude747]

Re: Possible to have a CPU with one bad core?

What make and model psu are you using?

[Uranium-235]

Re: Possible to have a CPU with one bad core?

more likely bad memory before a bad cpu

[ishelly404]

Re: Possible to have a CPU with one bad core?

The PSU I am using is a Seasonic X series fanless 400w, but I used a crappy logysis 550 watt psu (more like 250 watt) for a few months before I knew better.

I ran memtestX86+ for 10 hours last night and the windows 7 memory test, and it showed no errors.

[Koda]

Re: Possible to have a CPU with one bad core?

How about before he jumps to troubleshooting and buying new hardware he does an OS reinstall guys?

[ishelly404]

Re: Possible to have a CPU with one bad core?

I have already tried reinstalling windows XP and 7 multiple times, but I still have the same problem.

[999999999]

Re: Possible to have a CPU with one bad core?

Having a core at 60% does not indicate a problem by itself, look at the Task Manager to see what is using this %. On the other hand, disabling a core and suddenly regaining stability would suggest it is faulty. Run Prime95's stress test and see if one core routinely produces errors. You might also try removing the heatsink, cleaning off thermal pad goo and putting some grease on and reinstalling it. In rare cases if the heatsink doesn't sit right and heat conduct well, some areas of the core will run hotter than others.

However (and I may be wrong) I don't think inability to boot the Ubuntu CD is telling of a 4th core issue, AFAIK it should be booting off the first core alone until a certain point. When in the boot process does it stop? Forgive if an answer to that question receives no further input from me, I don't know all that much about Ubuntu multi-core support.

What else is in the system? Generally fanless PSU are a bad idea, because they only stay cool enough because the system fan(s) pull the heat into the case making the other parts run hotter as a result so you end up with either more fan noise as fans ramp up in speed to deal with it on a temperature adjusting fan control system, or hotter system components.

[larrymoencurly]

Re: Possible to have a CPU with one bad core?

What happens if you bring up the Task Manager and change the affinity of some of the tasks, even make them all use only that 4th core?

[Mad_Professor]

Re: Possible to have a CPU with one bad core?

I'll just save you some time, if you had a bad core, your computer would be crashing and running crazy slow and stuff would corrupt in memory.

Run prime95 or orthos overclock to stress test your system.

Run it up to 24 hours and the system will be slow and unresponsive during the test depending on how much ram you have.

If it fails, then disable the forth core and see what happens if that doesn't fix it, try other cores until you get it stable. If that doesn't work, check ram with memtest86. If it fails, test each stick individually until you find the culprit. If it passes, then swap out ide/sata cables try a different hard-drive/optical drive. If all else fails, switch out processor with another one or PSU or motherboard.

[ishelly404]

Re: Possible to have a CPU with one bad core?

I have already tried to run Prime95 with the 4th core enabled, and as soon as I click ok to start the stress test, Prime95 crashes. It runs fine without the 4th core or when I set it to only run three threads.

When I try to boot the Ubuntu LiveCD, it goes into a kernel panic almost right away.

I have tried reseating the heatsink, and even repaced the AMD stock cooler with a beefy Rocketfish RF-UPCUWR cooler and some arctic silver compound. The cpu idles at about 18°C, and at full load reaches about 30°C, so overheating probably isn't the problem. The psu is also barely warm to the touch.

The system is: MSI 880GMA-E35 mobo, AMD Athlon II X4 640 cpu, 8gb (2x4gb) G-Skill DDR3 memory, integrated graphics, Seasonic x-series fanless 400w psu, DVD-RW, 1.5tb hdd and 2 ati theater 650Pro tv tuner cards. The system is used as a DVR of sorts as well as for light use like internet browsing.

As for trying to change the affinity of some of the tasks, I will try that as soon as I get the chance.

Sorry about the long post, I'm just trying to answer everyone's questions.

[999999999]

Re: Possible to have a CPU with one bad core?

It does seem like you have a bad core but try one other thing. Disable two of the other cores and leave the suspect one enabled, then see if you get Prime95 crashes. If you don't then it would seem to be a power delivery issue but if you do, I'd see if your warranty covers an exchange and if not, just leave the 4th core disabled as you may not really need it for the described function of the system.

Also when running Prime95/etc for a test, you can just demote it to a lower priority level in Task Manager if you want to be able to use the system during testing.

[Topcat]

Re: Possible to have a CPU with one bad core?

FWIW, I had a socket 604 xeon 3.2GHz do this exact same thing. It was a bad cache on the CPU (which rendered the whole CPU useless)...while rare, it happens. The system would exhibit some really bizarre and seemingly random crashes and odd behavior. I was pulling my hair out...and as a last ditch effort, swapped the processors, it never gave me another bit of trouble. When I checked the individual CPU's, sure enough the L2 was failing testing.

[ishelly404]

Re: Possible to have a CPU with one bad core?

The system seemed to be stable for about a day with the 4th core disabled, but now there is graphics corruption, and firefox won't even start. What should I look at now? Is it possible that it is a problem with the onboard GPU?

EDIT: Just tried installing a ATI Radeon HD 5770 card, and it seems to be working, at least for now, but I will have to see how it holds up

[Uranium-235]

Re: Possible to have a CPU with one bad core?

try to RMA it to amd

also fwiw, I had a athlon xp 1900+ in my grandmothers computer that would not run at speed cause of a bad L2 cache. would run fine at about 112 bus speed

but in your case I don't believe propus arch has cache per core so its probably just a silicon defect. try to rma it to amd

[Th3_uN1Qu3]

Re: Possible to have a CPU with one bad core?

Yes, likely a northbridge issue with the graphics corruption. The CPU could be good after all. Try another motherboard.

[999999999]

Re: Possible to have a CPU with one bad core?

Could also be memory instability since it's using system memory for video. Boot to Memtest86+ and run that overnight to check for errors.

What is the history of this system? Had it been running in its present configuration stable for a while or a new build or a new OS installation? If a new OS installation you may have file corruption that causes all sorts of problems till you reinstall everything after system stability is established.

Just for the heck of it I would also pull the PSU and check it for vented capacitors, it almost seems like the system is progressively getting worse which is common as a PSU further and further degrades.

[ishelly404]

Re: Possible to have a CPU with one bad core?

I just tried the cpu in another system that I borrowed from a friend, and all four cores of the CPU seem to be working fine. The PSU also seems to be ok, none of the caps are vented. It doesn't seem to be a memory issue either, when the memory was installed in another system, it passed Memtest86 with no errors. And even though the graphics corruption was fixed by installing the Radeon HD 5770 video card, the instability wasn't.

I think that means new motherboard time.

[c_hegge]

Re: Possible to have a CPU with one bad core?

Yup, looks like it.