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Help! Computer won't boot after trying to overclock by just 10mhz

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June 11, 2012 5:10:53 AM

Bought a friends rig for super cheap (Radeon 4850, Phenom 9500 quad 2.0ghz, 3 gigs RAM), tried playing Diablo 3, got frame lag, decided it was a CPU bottleneck. Decided to try and overclock it just a tad...the ONLY thing I changed in BIOS was moving the FSB clock up to 210 from 200. Hit yes to save changes, after restarting comp the screen goes black and nothing. Restarted and same thing.

So I reset the CMOS, took battery out of mobo, reduced RAM down to one stick. Computer started fine and froze after 30 seconds of being at desktop. Restarted again. Then I got the BSOD "A clock interrupt was not received on a secondary processor..." Tried resetting CMOS again. Now it won't start at all.

Any ideas? I'm confused because I thought I did the right thing by only increasing the mhz by only 10. I didn't change anything else at all, not the voltage, etc so I don't see how I could've fried the mobo or cpu. So aggravating. For those wondering why I'm still using a phenom 9500, I'm saving up to upgrade now, but I'm strapped for cash and wanted this to last me for a few more months. I don't care about overclocking it anymore I just want it to run. Thanks in advance for any help.
June 11, 2012 5:13:38 AM

To clarify...when I say it won't start at all, I mean it won't boot. All the fans spin on the processor/GPU/I have power/etc, but I see nothing on the monitor, no response from keyboard or mouse, no beep by the motherboard like usual, etc.
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June 11, 2012 5:22:39 PM

Have you tried removing the GPU and running off the integrated output?

If you can get video that way, you'll want to go into the BIOS and make certain all the settings are where they should be, including RAM speeds and that the proper HDD setting is selected (IDE, ACHI, RAID)
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June 11, 2012 5:55:01 PM

By increasing the FSB by 10Mhz you also increased everything that relies on the FSB clock to power its own PLL by a proportional amount. For the CPU this is the CPU:FSB multiplier and for the DRAM this is the DRAM multiplier. DRAM does not have much headroom for overclocking at all. Some motherboards have separate clock generators for the DRAM but with integrated memory controllers this is no longer the case. Many new CPUs with locked multipliers are severely limited such that total system headroom is <5% so there may be nothing that you can do short of buying high speed ram or a CPU with an unlocked multiplier.
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June 11, 2012 8:21:53 PM

Well after several CMOS flashes and a fresh format/Windows 7 install, I am operational again.

Pinhedd, I didn't quite follow all of that, but from what I gather you're telling me I simply can't overclock this processor with my current setup. My RAM is Corsair XMS2 DDR2, 3 gigs. I'm sure its as outdated as the processor. Which is more of a bottleneck, the processor or RAM? If I buy better RAM will I be able to overclock the Phenom effectively? I don't think it would take much... all I want to do is be able to run D3 on 1024 res without lag, which seems more than reasonable given the video card (which is actually about to become a Radeon 5770 in a few days)

Thanks again guys.
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June 11, 2012 9:27:43 PM

evannnn67 said:
Well after several CMOS flashes and a fresh format/Windows 7 install, I am operational again.

Pinhedd, I didn't quite follow all of that, but from what I gather you're telling me I simply can't overclock this processor with my current setup. My RAM is Corsair XMS2 DDR2, 3 gigs. I'm sure its as outdated as the processor. Which is more of a bottleneck, the processor or RAM? If I buy better RAM will I be able to overclock the Phenom effectively? I don't think it would take much... all I want to do is be able to run D3 on 1024 res without lag, which seems more than reasonable given the video card (which is actually about to become a Radeon 5770 in a few days)

Thanks again guys.


It is a mouthful isn't it? It'll be easier if I explain with some numbers

The CPU doesn't have its own internal clock generator. There's no reason that it can't, it just doesn't. Instead the CPU gets a clock signal from a common source. On newer Intel machines this is known as the base clock. On older Intel and AMD systems this is known as the "Front Side Bus". This clock signal is pumped into a circuit known as a "Phase Locked Loop" or PLL for short. The PLL generates one or more output clock signals which are a function of the input clock, a scalar and a phase angle. The output clock has a frequency which is equal to the scalar times the input clock. The input clock naturally needs to be known ahead of time for this to work properly without creating causality problems but I don't want to get into a discussion about Fourier transforms. The scalar that I just mentioned is known as the clock multiplier. If the CPU has a clock multiplier of 16, it will generate 16 output clock pulses for every input clock pulse. If it has a clock multiplier of 0.5 it will generate one clock pulse for every two input pulses. So, since the FSB frequency is fed into the CPU the CPU's frequency becomes a multiple of the FSB frequency. Increasing the FSB frequency by 10Mhz actually increases the CPU frequency by many times that; in my example it would increase it by 160Mhz.

The recommended way of overclocking is to simply leave the clock source alone and bump up the clock multiplier. On systems with an unlocked multiplier this is easy and involves very little effort. On systems with a locked multiplier it cannot be increased (although it can be decreased to save power) or the increase may only be temporary (turbo mode). On systems with a locked multiplier the only way to overclock the CPU is to increase the frequency of whatever generates its input clock and this happens to be the FSB. However, this also increases the frequency of everything else that relies on the same clock source and this often includes the DRAM. A 5% increase to the CPU's frequency is usually no problem for most CPUs but a 5% increase to most non-enthusiast DDR2 DRAM will be enough to render it unstable. Fortunately, there are a couple of workarounds

1. Loosen the memory timings. Memory timings are measured in clock cycles and increasing the frequency of the DRAM shortens the period of the clock cycle which in turn decreases the configured latency. However, the DRAM modules might only be functional at the old latency so loosening the timings (increasing the number of cycles) may bring things back in line. You can also try overvolting the memory by 0.05 volts to 0.1 volts and see if this helps

2. Change the DRAM multiplier. The FSB on many chipsets is extremely forgiving, at least on Intel platforms. If your DRAM IO bus is running at 400Mhz (PC-6400 or 800 Mega transfers per second thanks to DDR) then this has a 2:1 DRAM:FSB ratio. Most chipsets also support ratios such as 3:2, 4:3, 5:4, and 1:1. If you drop the DRAM ratio from 2:1 to 3:2 you'll be cutting off 25% of your memory performance BUT you'll then be able to increase your FSB by 33% (trivial on most chipsets) to bring it back up to where it was before. In numbers this goes:

200Mhz FSB * 2 = 400Mhz DRAM

200Mhz FSB * 1.5 = 300Mhz DRAM

266.67 FSB * 1.5 = 400Mhz DRAM (back to where it was before but with higher FSB)

With the higher FSB you will also want to lower the CPU clock multiplier to keep it in line with where it was before the FSB value was changed and test it. Then increase the multiplier step by step and testing it along the way to overclock the CPU
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June 12, 2012 2:53:47 AM

Wow...so basically I'm an idiot and didn't do enough reading prior to trying to OC. I've just been so frustrated that I'm getting unplayable lag in a game that my friends are playing with significantly weaker systems that I kind of rushed through reading about it. After doing more research I've decided overclocking is not the answer as I should most definitely not have to with this setup...hopefully I figure out whats wrong.

Thanks again for your help guys.
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