Fake NVIDIA replacement GPUs?

Dear All,

I am trying to repair a 2008 iMac NVIDIA 512MB video card, which is apparently an Apple-specific 8800M. I'm pretty sure it's a bad GPU -- reflow worked for one day, then crapped out again -- and we have a BGA rework station at my university workshop, so going to give a replacement GPU a shot.

There seem to be a lot of stories out there about how NVIDIA GPUs from this era were faulty, (though I got over six years out of mine so can't complain too much). Looking around Ebay, I notice that there are at least two kinds of (supposedly) new G92-700-A2 GPUs out there: (i) 2008 chips, presumably from the same era as the one I'm trying to replace, and (ii) "2010+" chips -- these are listed as "G92-700-A2 128bit 256MB", which makes me worry that the memory bus width is wrong (according to the datasheets I've seen, the G92-700-A2 should have a 256bit memory interface). I also don't understand what "256MB" refers to in this context.

So my questions are: Are these "new 2010+" G92-700-A2 chips real? Did NVIDIA really make later runs of chips, possibly with half the bus width? And if so would these be a viable replacement for the 2008 GPU on the 512MB iMac card (perhaps with a performance hit)?

I should say that I'm just trying to get more life out of an old but otherwise working machine, it's obviously not for gaming. So maybe a new 2008 chip would be okay if I run the fans a bit higher and try to manage the heat more carefully (consensus seems to be that heat is the cause of the high failure rates for the 2007-08 GPUs). But if I'm going to all this trouble, a newer chip with a lesser failure probability would be preferred.

Thanks in advance for any thoughts.

 

nVidia didn't make reruns of their GPUs as far as I know. They likely produced chips for a set amount of time to supply laptop manufacturers. There has been different versions of a given GPU model in the past with varying bus width, etc. (see the GT555m as an example, that thing was a mess). Still in the end, I wouldn't even bother with it, you got a solid 8 years of service from your iMac, this is more than most people can expect out of their computers. I'd say it's time for an upgrade, once it starts going like that, it's either replace the component with an actual Apple part or move on.

 

have to agree with Tijo on this one. get a new GPU card or replace the iMac. I had 3 of those units that kept frying the GPU cards and Apple was kind enough to have Nvidia custom neuter the chip a bit and I have heard of very very few successful chip transplants about the only DIY repair successful was remove the chip and have someone fully reball it and then reattach. ( upwards of 70 % ran well if done properly and the rest of the board was good )

 

your system is probably a good example of where they MIGHT make some kind of weird stunted version, however, it really didn't happen that often, nor does it still with high end cards.

there's not really any such thing as a fake chip, if there is, it would be the equivalent to a scammer selling you a dummy//display smartphone when you expected a real functional thing. the manufacturing costs involved in making a fake Nvidia BGA and still allow it to function are probably pretty prohibitive to scammers.

you should probably be more concerned with compatibility. unless you're buying one specifically listed as compatible with your imac, chances of it working fully might be slim. that said, if you can pull a vBIOS from your original card and its not a special board revision, this might work http://www.ebay.com/itm/NVIDIA-Quad...061483?hash=item4d384d246b:g:M2oAAOSw-W5UwABr

its essentially the same chipset and a very standard card, also i always found these to be better taken care of than ones pulled from gaming systems.

i should add i don't know much about imacs. they might have the vBIOS loaded in with the system BIOS. if it turns out that for some reason you can use just about any MXM 2.1 card, this is by far your best option http://www.ebay.com/itm/Dell-MSI-Gr...413979?hash=item2a562cf79b:g:lzQAAOSwgQ9VzrbO its NOT defective, its a B1 revision 55nm chip that will also run cooler. (i'm really surprised it's been listed and unsold so long)

 

Many thanks for the replies so far. I've called several repair shops and apparently parts for these iMacs are long gone. I agree that something so old normally doesn't warrant this kind of effort, but it bothers me to toss out an otherwise working machine, and I'm curious to give a BGA replacement a try -- if it doesn't work, then I'm in (almost) the same situation.

I too am no expert on these things -- I know that there were only two cards that originally shipped with these iMacs, the NVIDIA "8800GS" (really a 8800M) and the Radeon 2600 PRO. The cards that niffcreature linked (thank you) certainly look to be the right format, but what I've read gives the strong impression that no other cards are compatible unless you flash a custom Apple BIOS, which I would have to figure out how to do. I'm probably overly optimistic, but since I have access to a BGA workstation right now it seems easier (and cheaper) to just drop a new GPU on the board and cross my fingers.

So, for the sake of argument, if you'd decided to replace the GPU with a "new" one, would you go with a 2008 G92-700-A2 that was fabricated before the chip you're replacing, or with a G92-700-A2 that was supposedly made several years later, and might have half the memory bus width?

Thanks again.

 

MXM format video cards were never exactly interchangeable between brands. The vBios is often manufacturer specific rather than being universal and the computer can't communicate properly with the cards if it's the case. MXM is basically the connector form factor and then even the PCB design can differ between brands. That's why sometimes cards from other manufacturers are compatible and sometimes they aren't.

 

i forgot to mention, a lot of ebay sellers are pretty terrible at giving accurate descriptions for stuff like this. isn't it not really possible for a g92 card to have half the memory bus? anyone else wanna chime in here?? i think it's safe to say its pretty extremely unlikely

 

Thanks again niffcreature, that's exactly the kind of thing I'd like to know: If the chip says G92-700-A2 on it, and it's not a fake, I would assume it can replace any other G92-700-A2 chip, but this "128bit 256MB" business has me spooked (recall we're only talking about a GPU chip here, not a whole card, so it's just not clear to me what these numbers mean). I've emailed the Ebayer in Taiwan for clarification, but not holding my breath for an answer.