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How to change the FSB on a MDD


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#1 Unknown_K

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Posted 24 February 2012 - 08:23 PM

I am thinking of getting a 1.25GhZ DP CPU for my 867 DP MDD. Has anyone done the hack to change the FSB to 166 from 133, if so how? My RAM is PC3200 so the speed increase will not be an issue.
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#2 Anonymous Freak

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Posted 24 February 2012 - 08:37 PM

As far as I know, there is no known way to increase the bus speed. I've seen instructions on how to increase the multiplier (involves desoldering and resoldering micro-resistors on the CPU card,) but not the bus speed.

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#3 Unknown_K

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Posted 24 February 2012 - 08:41 PM

Well the CPU card would not need changed because it would be at the stock speed.

The 867 DP is set to 133 FSB so I figured there should be a way to jack it up to 166 like the 1ghz and 1.25ghz DP machines (why would Apple make 2 different boards).
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#4 Byrd

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Posted 24 February 2012 - 11:36 PM

Plenty of info on the mod

http://bitsandpieces...Multipliers.htm

http://www.xlr8yourm... ... odule.html

... I also recall a guide on the Macbidoulle/Hardmac site, but can't find it (it was most relevant to the 133 to 166 FSB overclock)

I recently aquired a later model FW800 single 1Ghz machine, 133FSB, and could not get it up to 166FSB - it just reported the former 133 FSB. I suspect the later model boards are fairly different. It also had issue with a PC flashed Geforce 6800 Ultra, which worked fine in other Macs (pins covered etc).

If the 166FSB alteration doesn't work, there is always adjusting the multiplier on the CPU card itself; for a 1.25 DP you should get 1.42 out of it.

JB
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#5 Unknown_K

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Posted 24 February 2012 - 11:56 PM

Did the 1.25Ghz CPU have a copper heatsink, mine is Aluminium?
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#6 BGoins12

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Posted 25 February 2012 - 01:18 AM

The Dual 1.42 had the copper heatsink, the rest were the thick aluminum or thin aluminum ones.
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#7 waynestewart

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Posted 25 February 2012 - 03:51 AM

Did that once. It's not hard
There's resistor settings on both the motherboard and the processor card for determining bus speed. If either one is set to 133mhz then the bus will run at 133mhz. If you're changing the processor that would solve that problem.

To change the resistor setting on the motherboard you need to remove R676. It's located on the bottom of the motherboard right under the rear left corner of the processor socket.

In case you want to play with your currant processor. On your dual 867 card you need to remove resistor R22 to change it's bus setting from 133 to 167. It's on the top of the card to the rear of the left hand processor. If you don't do anything else your 867 will be trying to run at 1083mhz. It may or may not do that. Mine had 933mhz processors and handled it but I may just have been lucky. There's lots of info on the web on overclocking MDDs. I should point out that there's a separate set of resistors for the speed setting of each processor.
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