iMac 24" big problem - repair

[orangezorki]

Hi Mekintoch,

Something is futzed (technical term, apologies if my all-encompasing Mac prowess is difficult to understand)* with your graphics for certain. I suspect that the 14MB vram you saw in windows is the cache required to hold just the display bitmap for your screen - reminds me of when I was a kid getting a Bondi iMac making sure I (My Mum) bought a Rev B with a whopping 6MB of vram so I could display 'millions' of colours at 1024x768! Something is at least stopping you from using most of the graphics memory, and perhaps any acceleration at all, which might account for why windows worked at all, when OSX didn't. I don't know if Windows uses any acceleration for its desktop, but OSX definitely takes advantage of what it can get.

If your GPU hasn't been changed (which seems to be the case from your posts), then that would be the next logical step. My only worry is that it is not impossible that something bizzare has happened to your PSU that is over or undervolting some major components. Unlikely, I know, but I wouldn't want you to throw good money after bad. I guess the silver lining either way is that if you still have the old mobo, it should be good, and you could sell it to get most or all of your money back.

David.

*My head hurts when I open the Terminal, and I've only recently stopped using my elbow as a spudger.

 

[Mekintoch]

Hi Mekintoch,
Something is futzed..........

Thank you David Orange Zorki for support.
Sure, before trying a new GPU, I can check the PSU, that I'd already gived a check yesterday by eye, the Caps seems all fine, but I will like to make an extended test,

when unmounted, do you know if there is a way to turn it on so I can check the voltages? (like on PCs, where you just close contacts between green&ground cables on pinouts with a paperclip) ....and I can't find the pinout voltages on the net, maybe somebody that chew a more technical english can help me.

...In case I can check the voltages when mounted and running, when under stress at boot, maybe better...?

About the 14MB Gpu Vram, I think even windows use acceleration, because (forgot to tell) it has no image, complete black desktop.

 

[orangezorki]

Thank you David Orange Zorki for support.
Sure, before trying a new GPU, I can check the PSU, that I'd already gived a check yesterday by eye, the Caps seems all fine, but I will like to make an extended test,

when unmounted, do you know if there is a way to turn it on so I can check the voltages? (like on PCs, where you just close contacts between green&ground cables on pinouts with a paperclip) ....and I can't find the pinout voltages on the net, maybe somebody that chew a more technical english can help me.

...In case I can check the voltages when mounted and running, when under stress at boot, maybe better...?

About the 14MB Gpu Vram, I think even windows use acceleration, because (forgot to tell) it has no image, complete black desktop.

Hi, good to see that someone appreciates my jokes!

I'm really sorry, but I have never had a power supply problem, so have not had to open one up. In any case, if the PSU was the problem, I think that diagnosing something like this would be very difficult. Personally, I'd check the costs of a replacement PSU and GPU, weigh them up with the likelihood of them being the solution, and go from there. Again, please consider getting a base 21" iMac instead - it has the same resolution as your 24", will smoke your machine, and has a warranty so you won't have to go through this hassle for at least a year.

Daivd

 

[Mekintoch]

I understand what you mean, the reason it's that I don't need a faster HW and a smaller screen (for the real use of it), and I can save some money.

I've tested the PSU all voltages are stable and perfect, even under stress.
lines available 12V - 3.3V (4.0V for switch on) and 2.1V autoregulated.
Simple Test, seems all regular.

About the Geforce 8800GS, 've tryed different drivers in win7, everytime installation completes succesfully, but after the reboot that Nvidia ask, the GPU it's again not recognized, and need to reinstall................. hope I got it right.