Classic Mac Hardware (Troubleshooting, Upgrading, & Modifying) > Mac CPU Upgrades

MDD 866 Mods

(1/15) > >>

Old article about unleashing the 166 bus on first MDDs

--- Quote ---Many thanks to Amber's eyes who compared the 2 computers under a magnifying glass for 2h30, Pimus for lending us a brand new G4 Bi-1GHz and Bakayo for his incredible welding skills.
Here are the modifications needed to change the G4 Bi-867's bus clock from 133 to 167MHz.
You'll note that changing the bus speed to 167MHz would overclock the CPU to over 1GHz. To prevent this, you'll have to change the CPU's multiplier coefficient from x6.5 to x6.
WARNING : for your computer to remain stable, you have to use DDR-SDRAM PC2700 modules. The usual PC2100 modules are not certified for working at these kinds of frequencies.
--- End quote ---

--- Quote ---Note that to get the bus from 133 to 166 Mhz, overclockerait machine more than 1 Ghz. To avoid this, you must retake the multiplier of 6.5x to 6x (see this news )
Watch out !!!!!
To ensure the stability of the machine after changes, it is imperative to have only DDR-SDRAM PC 2700! The strips are not recommended 2100 !!!
Changing bus takes 2 steps:
1) changes on the motherboard (the Word is Amber)
the photo is the underside of the motherboard.
I surrounded the three resistors in question.
They are in order R677, R678 and R676
--- End quote ---

--- Quote ---a bus for 133mhz: there is a resistor at each location
for a bus to 167MHz: you must turn in the R676
(It's about 100% on because I had 2:30 to scan both cards under the microscope and that's the only difference)
So there must be other possibilities (I have not taken the time to try and ram no longer lends itself to such practices)

Apple has added a second protection on Bi 867 cards If you just change the settings on the motherboard only does it happen in 167 Mhz on the condition to map a 1Ghz or 1.25 bipro Ghz.
So I'll turn it back to Amber:
So on the map girl pictured, there is a series of three resistors
numbered as follows.
Bus 167 Mhz
R27 nothing
R22 nothing
Resistor R26
Bus 133 Mhz
R27 nothing
Resistor R22
Resistor R26
So it is a security or a lock over Apple
--- End quote ---

--- Quote ---In this screenshot, you see the bus at 167 MHz. The processor board is that of a true dual 1Ghz, not Overclock.
--- End quote ---

On Mac-Forums one guy make this...

--- Quote ---I have succesfully overclocked Dual G4 867mhz machine by changing the FSB from 133mhz to 166mhz, I removed the two resistors, R676 and R22. I have tested that the machine is stable in Xbench 1.3, Geekbench and in normal usage. G4 chips in my machine are RX933PC so they are rated for 933mhz and now working at 1080mhz.

But, I looked up the Samsung L3 cache chips on my processor card and as far as I know, they are rated for 250mhz (-HC25). L3 cache in MDD models with 1MB of it operate at 4:1 ratio, meaning that the cache in my machine is already operating out of spec, at 270mhz.

Is there any software which I can use to verify the L3 cache speed? Xbench displays incorrect speed, ~4Ghz. I wonder if there is a way to modify L3 cache ratio to 5:1 so I could possibly overclock even further, to 1.25 Ghz? Probably I could just try and see if it can take it, but I would like hear if anyone in here has ever done overclockin for their Dual MDD 867mhz machines and was it how succesful?
--- End quote ---

Here is the "bible" of MDD cpu modules overclocks

This section refers to 1420MHz modules only  :-[

Below is the multiplier table for the 3-Phase LTC3732CG - Note the default voltage for the 1420MHz module is 1.60V


 Front PLL_CFG array

 Back PLL_CFG array

Voltage regulator


Anyone willing to take 133 bus MDD to a higher ground?


[0] Message Index

[#] Next page

Go to full version