Just got El Cap 10.11.6 running on a 2007 Dual Quad 3GHZ 2,1 CMP with an EFI FLASHED HIS HD 5870.
Used
dosdude1's Youtube vid
- very straight forward.
Created the USB installer - installed 10.11.0 to a spare spinner HDD on my MacBook Pro - replaced the boot.efi in the required places.
Installed the drive in the 2,1 - booted up. OK - copied 10.11.6 combo to the 2,1 El Cap - ran the 10.11.6 combo -rebooted but of course wouldn't boot so removed teh drive to my 4,1>5,1 cMP and re-did the boot.efi replacement.
Put the El Cap 10.11.6 HDD back in the 2,1 - cold boot up - Voila !
SIP is still enabled aand next I'm going to replace the boot.efi in the El Cap Recovery disk.
Then I'm going to Carbon Copy Clone the El Cap drive to a small spare 2,5" spinner HDD for future use.
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Luckily I already had this ( friend's ) machine running Mavericks 10.9.5 on another drive - this was handy in having a separate OS X working eg: to check if El Cap shows up in Mavericks Startup Disk etc.
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Incidentally, I had a problem with the 2,1's CPU B ( bottom one ) showing as dead but I have a strong feeling that cleaning the CPU B's CPU socket & the 3Ghz chip with IsoPropyl ( with a soft brush ) may fix that - in the meantime ( until later today ) This 3Ghz 2,1 is running quite snappily ONE 3GHZ CPU A ( completely removed CPU B and placed soft plastic cover over the CPU empty socket with the CPU Clamp locked down until I can get to cleaning it tonight
If I can't get the CPU B chip working, no great loss. One 3Ghz is still respectable speed and ample for my moderate-user friend..
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The amount of dust under both heatsinks was absolutely astonishing ! I will be posting re this in another thread.
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A nice day's work, very satisfying to breathe new life into these. remarkably long-lived and still very useful .machines
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EDIT : I did a 200% absolute cleaning ( isopropyl alsohol + soft brush ) of CPU B's CPU chip and the motherboard CPU socket in the 2,1 - re-thermal pasted and re-installed ( I'm getting quite adept at this !
) but no joy. . it seems that the CPU B's X5365 3Ghz is truly dead - so I removed CPU B + heatsink, sealed the motherboard CPU B socket - it is now a SINGLE QUAD Core 2,1 until a replacement AliExpress X5365 arrives.
In any case El Cap 10.11.6 is running without any issues for the time being.