Chosen Solution

Hi Hoping to upgrade my mid-2007 24” iMac to a ‘Penryn’ CPU, I very carefully read/absorbed lots of detail descriptions/accounts of how/why/what not to do, followed them meticulously and fitted a (allegedly) new T9500 CPU. All back together, I plugged in and tried the start button. Nothing - apart from the usual two quick buzzes from the optical drive. Took the ‘glass’ and the alloy frame back off, tried again and the same result plus noted very small flick of the CPU fan. Numbers 1, 2 and 3 of the LEDs to the right of the memory slots come on but nothing else happens, no chimes, no screen illumination, nada! - and I waited 15 minutes in hope. Put the old CPU back in and away it goes, as reliable as ever. Fearing I’d missed something I’ve done the same exercise three times now, all with the exact same result. I now KNOW I’ve not messed up because as soon as I put the old CPU back in, Bingo! away it goes, perfect boot, everything. I’m writing this on it. There are lots of articles about how to do it, none mention any problems booting afterwards. There are only two posts that say the T9500/T9300 might be incompatible amongst the very many that say they are perfectly OK, other than speed reporting errors. The two I’ve found saying the CPUs are incompatible are effectively disputed in the following posts. To be candid I really don’t care if the speeds are reporting incorrectly, all I need is SSE 4.2, which the T9500/9300 have and that will allow me to install Catalina with a patch. Bottom line: Have I probably got, as I suspect, a faulty CPU, or is there somewhere some definitive information that says the T9500/T9300 are NOT compatible - and that incompatibility something is more than just the misreporting of speeds. Will Update (06/18/2020) OK, I understand the concept of the EFI not being able to use the T9500/T9300. That said, I have never (happily) had to dig into my iMac’s bowels to see if the conflict might be there. At the moment I’m on the latest (last ever?) update of El Capitan and I’d understood that any EFI upgrades came embedded within the OS updates as they were incorporated - or is that a misunderstanding as well? A couple of examples of what spurred me to try and give my iMac a new lease of life can be found in the following links: https://www.youtube.com/watch?v=JmLkRk3Z… (even if his technique is a bit off) and a whole series of articles like this from a well respected blogger, with very specific details regarding what will and what will not work: https://lowendmac.com/2018/penryn-t9300-… I’m running a Mid 2007 24” iMac 7.1 that I’ve had from new - apart from the screen size, just like the example used in the youtube I referenced. Is it possible there is some subtle difference I don’t know of that is foiling my attempt and could you point me in the direction of finding it please. It does seem a little hard to take that all of the youtubers/bloggers are full of it and peddling the theory for some reason best know only to themselves - unless, perhaps, to capitalise on the disposal of an excess of unsaleable T9300/500 CPUs? Will Update (06/30/2020) It’s fixed! It was a dud T9500. The replacement worked and booted straight up as soon as fitted. No one was ‘at it’, it’s not a myth, it works and was a bit of an undertaking but with care and attention, quite possible. The only thing not reported correctly is the CPU details and the FSB speed. Who cares? It is working and markedly quicker. Most importantly it allows upgrades to a later OS. To upgrade to Catalina, Dosdude1’s tutorial is excellent and all his patches and updates work well. Just make sure you follow it to the letter. I would put an image of ‘About this Mac up but can’t see how. A 13 year old iMac, running Catalina, for the outlay of £125 and a few hours of work and effort. Will

Its all about firmware! Intel CPU’s load some of their micro-code from the systems ROM (EFI in our case here). Apple never offered the T9300 or T9500 CPU’s so the micro code within the EFI is just not there! Sadly there are a few people who assume something works without doing it or understanding the limitations Apple imposes. I would make sure you have the newest EFI this series used as maybe it snuck in! I haven’t done this upgrade so I just don’t know if the issue is just a versioning issue within the EFI. The highest of the T series CPU’s Apple used was the T7700. Later on Apple did the X7900 as the Extreme and then jumped to the E series in the 24” models. So you have proved anyone telling us this series can support the T9500 is full of it!

@willumn - Will you are a champion ! Can you help me to understand if I can do the same ? I have a Mid 2007 7,1 24” and would like to go past ElCapitan. I love this iMac although I have a newer one and it would be nice to get some newer OS on it. I found the guides to upgrade the 20” but nothing about 24”. I bought a used T9500 which “should” be good, of course I have no mean to test it. I have 4Gb RAM, 500GB SD, the graphic card is the Radeon Pro HD2600. I have NO IDEA how to check EFI. Can you confirm it is the same setup ? And which instructions did you use to take it apart ? I took once off the screen to change the HD, but that is about it… Any other tips or advise ? (from anybody out there) Is there a way to check if e.g. the EFI is the same ? (assuming it plays a role of course) anyhow well done ! and Happy new year ! Angelo