Overclocking Need some info on 4850's

Hey everyone,

Not sure this is in the right section, if it isn't can a mod/admin move it please.

I am trying to OC my 4850 so it has a little more go in it, and I was wondering if I could get some info.

If a 4850 and a 4870 use exactly the same GPU, why can the core speed not be raised to 4870 standards? Is it the PWM's? (Obviously you can't raise the ram to the same speed as it's only DDR3, but in theory the GPU core should raise to the same speed that a 4870 can handle.)

I have a custom cooler on my GPU, and at stock speeds it only hits 49 degrees when under full load, so I should have plenty of OC room. Problem is I can only get about 12 MHz out of it before it becomes unstable. I think it may be a lack of power, is there a tool about that allows tweaking of the GPU voltages?

Any general advice (Apart for take it easy, which is obvious. ^^) about OC'ing a GFX card would also be appreciated.

 

4870 uses GDDR5 IIRC.

 

There's no soft way to change GPU voltages - extensive hardware modding (replacing resistors with variable ones etc...) is needed to raise them.

 

Yeah it is, which is why I mentioned the GDDR 3 not being able to make it, but the GPU clock should be able to in theory.

I was thinking of a way to tweak the voltages in the cards BIOS actually, I'm not so noob that playing at that level bothers me. lol

Probably need something like this: http://www.techpowerup.com/downloads/1283/TechPowerUp_Radeon_Bios_Editor_v1.18.html

 

Ehhh... you'd be safer going with something like ATITool. It will automatically and gradually OC the core for you until it starts artifacting - thus it gives the highest core OC guaranteed safe for your card every time.

- Diosjenin -

 

how hot is your card getting? I can max out my core and it still runs. But I have an aftermarket cooler.

 

I haven't fiddled with a GFX bios since nvidia 6800GT days, i had my overclocked for so long i thought 435Mhz was the stock speed!

It might just require a little boost in GPU voltage in order to get 4870 speeds, as all 4850's are just poor performing 4870 cores, hence the underclock.

 

38 degrees C at idle, and 49 after 10 mins at full load at stock speeds.

After a lot of fiddling I have managed to OC it too 665 core and 1038 GRAM before it starts to be unstable. At those speeds the card gets to 58 Degrees C after 10 min fully loaded. Air Cooled.

 

Overclocking levels are never guaranteed. The frequency a piece of silicon can support varies and as a consequence this produces the headroom used for overclocking. The better silicon will be used to produce 4870 so although you have the same GPU the particular chip you have may not be able to support 750MHz.

You may have to face the fact that the particular chip you have is a poor overclocker.