Did I just get a bad 640?

I've been working on overclocking the rig in my sig for the last week or so, and I'm running into some very disappointing results. I was wondering if anyone could help me out.

First, I wasn't able to include my chipset waterblock this time around, so now I'm using the Swiftech MCX159CU. I know it's making good contact, so I'm not worried about that. The other watercooling components are two Chevette heatercores in parallel with two Sanyo Denkis each in push/pull config @ 5v, an MCP655, MCW6002, and DD Maze4 GPU. Maybe that's OT, but I'm pretty sure my coooling is more than adequate. Even at 1.5v I haven't seen CPU temps over 36C or so, so I know that's not the problem.

The CPU just seems like it's requiring WAY more voltage than it should. At 3.9 I have to bump it up to 1.45/1.47v to get some stability, and even then it crashed one of last night's Prime95 instances. The same happens at 4GHz, but I have to pump it up to 1.51v for similar stability. I have done the vdroop mod, and the reported voltage stays very consistent. I've never seen more than a .02 variation from it. My rails simply don't budge on my Seasonic 600w.

I know it's not the memory...this is good TCCD, and it Primes away quite happily at 260x14 when I lower the multiplier...so it's got to be the CPU, right? My PWM temps no longer exceed 43C now that I added a fan over the heatsinks that were already in place.

Any ideas? Can I run more voltage through this? How much would be safe? If it's just a crappy chip, I feel pretty shafted by the classifieds user who sold it to me...

For WCing, 1.55v would be plenty. You might have gotten a dud, but .. normally 6xx series CPUs do like a 1ghz OC. If you can get like 4.1 outta your system, dont be disappointed.

how high will it go on stock volts? most i've seen do close to 4ghz. how fast did the seller tell you s/he ran it? with similar components? have you tried asking him/her?

everything looks good, it seems you've taken everything into consideration. mind you i don't own a 6xx, hopefully someone else has some insight that can get you flying.

Where is the chip from (country it was manufactured in)? The China chips seem to do worst than the Costa Rica and other chips. The China chips seem to need more voltage for less of an OC. If you are dead-set on reaching 4ghz+ and you have a China chip...I'd say just move your china chip for cheap in the classifieds and go buy another. The 6xx's are fairly cheap now a days and hopefuly you will get a Costa Rica chip.

how high will it go on stock volts? most i've seen do close to 4ghz. how fast did the seller tell you s/he ran it? with similar components? have you tried asking him/her?

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They said 3.8 at stock volts, and it's around there with what I have. Took a vdroop mod and watercooling to do it, though. I'm pretty sure it wasn't manufactured in China...it was either a Malaysia or a Costa Rica.

I've seen several people do 4.0GHz with around 1.47v or so, so I thought this was underperforming. It's just not responding to voltage like I thought it would.

I have 630 from China and it can do 3.8 @ stock volts but needs 1.42V is for 4Ghz on air.

My costa rica 640 on air.It runs 1.475Vcore at 4G and 1.65Vcore at 4.32.

holy cow, you run 1.65v on AIR??!

Yup, dual prime95 stable at 55-57C and no throttle with throttle watch.
With 2 xp-120s soldered together.

johan851 said:

I feel pretty shafted by the classifieds user who sold it to me...

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I hate to say it but no 2nd hand chip is going to clock worth a damn.

I hate to say it but no 2nd hand chip is going to clock worth a damn.

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You're right. Lately I've been wondering why I bought it second hand...if it was a good clocker, why would someone sell it?

Either way, not bad results.

i wouldt complain to much either, some chips might just not overclock as much...

i just bought a 2nd hand 830 for a really low price and its seems to be a golden chip

I'm having the same problems as you man. To run 4ghz (250x16) I set my vcore to 1.5 and while running prime95 my computer would restart.

Sentential said:

I hate to say it but no 2nd hand chip is going to clock worth a damn.

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Mine does just nicely.

Personally just about everything I have bought used does clock nicely. My 505 is at 4.5ghz which on water i'm pretty happy with. My 550 for the 10 mintues I played with it did 3.8ghz like cake why does used stuff clock so badly may I ask.

why does used stuff clock so badly may I ask.

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If it was worth keeping in the first place, the first user wouldn't be selling it.