[fenderjaguar]

I had a Radeon HD4850 512MB and used to overclock my E5200 CPU to well over 3ghz. Now today I've just installed a Radeon HD4890 1GB and for some reason I can't overclock the CPU at all now. If I try to, then it just shows the bios screen, then reboots and reloads the standard 2.5ghz clockspeed again.

Does anyone know why this is happening?

[crjdriver]

I can think of a few reasons;
1 Pw supply. The 4890 uses more power
2 When you overclocked the cpu, did you lock the pci-e bus or were you overclocking the pci-e bus also?
3 Components just wear out. You can have a stable OC for a while and one day it just will not work any longer.

[fenderjaguar]

Originally Posted by crjdriver

Pw supply. The 4890 uses more power

I initially thought this myself, since a 500 watt PS was recommended. But I can't even overclock it a tiny bit. If it was the power supply, I would expect to be seeing things go belly up when I got to a certain point, not for it to just cease to function when overclocking just a couple of mhz, yet work perfectly at the stock speeds.

Originally Posted by crjdriver

When you overclocked the cpu, did you lock the pci-e bus or were you overclocking the pci-e bus also?

Not sure what you mean here. Are you talking about overclocking in catalyst, or altering the frequency of the pci express port in the bios? No, I wasn't overclocking and I had the frequency on auto and tried it on 100 (which is standard) also.

Originally Posted by crjdriver

Components just wear out. You can have a stable OC for a while and one day it just will not work any longer.

Nah, would be a bit of a coincidence that it happened at the exact same time I installed this new card . I'm pretty sure I could put my old card in or use the integrated graphics and be overclocking again. Infact I suppose I'll have to try things like that to rule it out (what a ball ache).

Thanks for the suggestions.

[crjdriver]

When you up the fsb, you are also overclocking the pci/pci-e bus unless you lock it.

Remember just because you have always overclocked a given part does NOT mean you can overclock it now.

[fenderjaguar]

I see. How do I lock it?

Also, I can't underclock the fsb, either. It will only work at 200mhz. If I set it to 199 or 201, the computer won't boot up at all and just resets back to 200.

[crjdriver]

I see. How do I lock it?

Read your manual. Each bios is a little different so giving detailed instructions would be difficult. Note some lower end boards do not have this option.

[fenderjaguar]

Yes, I pretty much understand how the bios works and I've read the manual cover to cover. I've also just flashed the bios to the latest one, downloaded from the gigabyte website, just incase that had something to do with it.

So do you mean the PCI-express frequency? The options are from 90mhz to 150mhz. With an "auto", which sets it at 100mhz. Like I say, I've tried it at 100 mhz (and even 90mhz) but it just won't boot unless the fsb is 200mhz...

[crjdriver]

Yes, that is it. Auto does set it at 100 as long as the fsb is stock. When you up the fsb, you also up the pci feq. When you set a hard value, ie 100, then it is locked at that value and will not go up with the fsb.

Have you tried clearing cmos then attempting an overclock?

Next you might just have to accept that it will not overclock with that combo. Remember there is no guarantee that you can overclock any part. What you get is what you get.

[fenderjaguar]

Yes, I have already set it to 100mhz and it won't overclock.

When you say clearing cmos, do you mean just loading up optimised defaults in the bios or do you mean physically switching one of those jumper things on the motherboard?

Cheers.

[crjdriver]

Clearing cmos is moving the clear jumper to the clear position for at least 15 seconds. To properly clear cmos;
1 Unplug the system
2 Press the pw ON button 2~3 times to remove any residual charge from the pw supply caps
3 Open the case and clear cmos with the jumper
4 Replace jumper to "keep" position
5 Replace pw cord and pw ON system. Enter the bios and load optimized defaults. Save settings and restart. Again enter the bios and set any settings you need ie sata mode, voltages, etc.

[fenderjaguar]

More woes..

So I figured if I can't overclock anymore when I put a different video card (for seemingly no reason? I mean, yes I've taken the card out and even put different ones in and yes I can overclock when I do that. So it seems to be that this particular card doesn't like my computer or something). So I bought an E8400. Wonderful CPU. Boots the computer up quicker and overclocks to 3.6ghz. Lovely, right? Well, no. The card likes this cpu even less than it likes the E5200. Everythings works, but when gaming with the E8400 and the 4890, framerates drop like a stone! Performance is much much better with the E5200 (not o.c) and the 4890, even better with the E8400 (o.c to 3.6ghz) and a 4850. At least the 4890 worked as it should do with E5200 (even though I couldn't overclock the CPU) you would think it would work normally with an E8400 that wasn't overclocked as well, right? No.

What an earth is going on here? You can see what my power supply is, a coolermaster real power 520w. Could it be that? I notice the 4890 takes 2 6 pin power leads, whereas the 4850 takes just one. Do you think I need a bigger power supply? I just can't see it myself. I would expect to load up games and crash, rather than just have poor framerates.

Any help would be appreciated. Thanks.

[crjdriver]

Since the 4890 requires a min of 500W and each 6pin lead must supply a min of 75W, you are right at the min requirements.

If it were me, I would not attempt to run that card with <600W and at least 50amp on the 12V rail[s]

[loserOlimbs]

Originally Posted by crjdriver

Since the 4890 requires a min of 500W and each 6pin lead must supply a min of 75W, you are right at the min requirements.

If it were me, I would not attempt to run that card with <600W and at least 50amp on the 12V rail[s]

Agreed. Running right at the minimum means your going to kill something. Either the PSU or a component.

I just picked up a new OCZ 700w Xmodstream (or something like that at least)
49.99 after Mail in rebate, and it dropped 3$ today.

[fenderjaguar]

Thanks man. I read your post, then whizzed out to get a new PSU. I got the coolermaster silent pro m 700w. Everythings fine now, though I still can't overclock the CPU with this card. Still, the cpu is very good, even running at stock speeds.

Thanks.

[crjdriver]

Glad it worked for you.