Sidebar Sidebar
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.

VBIOS for ATI Radeon HD 4850 from an iMac 24" early 2009 A1225

T

TheLastDay

macrumors newbie
Original poster
Apr 8, 2021
3
0
Hi everybody,

I am in trouble since weeks since I decided to upgrade my iMac 9,1 early 2009 24".
I upgraded the CPU for a 3.06GHz and replaced the stock NVIDIA GT120 by an ATI Radeon HD 4850.

My idea was to boost it to sell it for a better price and to do a little bit of hardware stuff.
CPU is done and OK :).
GPU is the trouble.
I got the ATI Radeon HD 4850 card from Aliexpress and the heat sink adapted to my 24" iMac from ebay.
When I boot : Black screen !!!

After long search on the web, I found a post describing the same issue.
I tested the solution with an external monitor with mini display port and YESSSS it works.

But still nothing on iMac internal screen. After lot of search (vbios check, dump through Windows, search on Netkas, insanelymac, macrumors, macbidouille ...) my conclusion is that my card comes from an iMac A1312 (late 2009 27") and its bios is not compatible with my iMac A1225 24".

My BIOS has right size of 128K, with and EFI part, the card ID is an 0x944A.
But the ROM version is 113-B9110A-383 with an EFI version 01.00.383.
And I need a ROM version 113-B9090C-181 with EFI version 01.00.327.

Is there a kind soul who can do a dump from his stock ATI Radeon HD 4850 from a iMac 9,1 early 2009 24" ?
Or tell me where I did a mistake in my investigation if if there is another solution ;)!

Thanks for your help

TheLastDay
 
Krazubu on MacBidouille gave me an advice about investigating inside Mac OS Install dmg files for some EFI file that could include the right vbios data.
I started to dig ...
 
TheLastDay said:
After long search on the web, I found a post describing the same issue.
I tested the solution with an external monitor with mini display port and YESSSS it works.

But still nothing on iMac internal screen. After lot of search (vbios check, dump through Windows, search on Netkas, insanelymac, macrumors, macbidouille ...) my conclusion is that my card comes from an iMac A1312 (late 2009 27") and its bios is not compatible with my iMac A1225 24".
Click to expand...

I can't really help you, but consider this:
HD4850 works fine on your iMac early 2009, as you have described.

The remain problem is to get it control and send signal to the internal monitor.

And the hardest obstacle is to get them talk with each other.

Reason:
Internal LCD panel of iMac early 2009 uses LVDS protocol (capped at 1920 x 1200)

On iMac late 2009 it uses eDP protocol (to suit the 2k resolution)

While these use the same LVDS 30-pin connector, their are different protocol.

Verify this in System Preference.

You will need to modify the VBIOS on the card, or EFI on the Mac OS disk, or both. I don't know.
The gain in performance is marginal, comparing with the stock GPU GT120

I would just sell them separately.
 
Last edited:
You must log in or register to reply here.
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.
Top Bottom
Back