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You are here: MacNN Forums > Enthusiast Zone > Hardware Hacking > Yay! Upgraded my iMac G5 logic board

Yay! Upgraded my iMac G5 logic board
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Mac Elite
Join Date: Feb 1999
Location: California
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Jan 24, 2013, 04:25 AM
A few months ago the GPU started screwing up on my 20" rev A iMac G5, so I started hunting around for a replacement. I found a logic board from a 20" iMac G5 ALS (rev B), and after some studying online, figured it would work in my machine. And it does.

Although the boards have different model numbers (820-1540-A vs. 820-1747-A), they've got the same shape and configuration for all the necessary connectors, and only a few differences. The rev B board supports a different Airport card, but I hardly ever used wireless anyway. It's also got one of the screw holes for the CPU heatsink gasket in a different place, so I was only able to screw in one side. For a better seal, I used a bit of electrical tape. I was worried this still might not not cool the processor as well, but after using the machine for a while the temperature reading seems to be normal.

And the funny thing is, a while ago I was telling my roommate that these computers weren't made to be upgraded.

EDIT: also, the lower CPU fan connector is on the right side of the ALS logic board, rather than on the left side of the original G5 board. It required rerouting the cable from the fan, which itself required unscrewing the metal frame so I could get at it. That was a pain in the @$$, especially since one of the screws was in there pretty tight, but it worked.
( Last edited by Patrick; Jan 25, 2013 at 03:35 AM. )
Grizzled Veteran
Join Date: Jun 2006
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Mar 29, 2013, 12:54 PM
congrats. i know you're proud.
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Patrick  (op)
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Join Date: Feb 1999
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Mar 31, 2013, 12:27 AM
Thanks. I'll admit, though, that with all my careful planning before I bought the thing, I hadn't noticed that one of the fan connectors was on the other side of the board. I got lucky that the new one was within easy reach of the fan cable I already had. All in all, an interesting foray into computer assembly, and cheaper than buying a used iMac off eBay.
Join Date: Jun 2000
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Apr 1, 2013, 12:41 PM
congrats! that sounds daunting.
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