Overclocking iMac G4 800mhz

Doward

macrumors 6502a
Original poster
Feb 21, 2013
526
8
Anyone know offhand which resistor bank controls PLL? iMac 17" 800Mhz G4. Looking to move it up to 900Mhz is all.

Thanks!
 

justperry

macrumors G4
Aug 10, 2007
10,175
5,319
Home is everywhere and nowhere.
Don't even bother, I overclocked my Pismo long time ago, from 500 to 550 MHz, unstable and does not make much of a difference.
I said it before and say it again, if you want a faster Mac buy a faster Mac, overclocking does not give you much of a speed boost.
Even a PATA/IDE SSD would do more than overclocking.
 

Doward

macrumors 6502a
Original poster
Feb 21, 2013
526
8
Don't spread defeatism Perry ;) :p

OP: here you go http://thundernerd.com/iMacG4Chart.html

Been here, done that. New decent thermal paste and good dusting is a must.
Much obliged, sir! Freebie system needs a little Leopard breathed into it. Now to dig through the old ram, see if I can make 1GB out of it ;)

*edit*

Very interesting. Cleaned the CPU, and I've got an XPC7451 800Mhz - not an XPC 7450 800Mhz. Wonder if 1Ghz might be in the cards ;) Also noticed I do have two points that the heatsink interfaces with the casing (dual heat pipes).

I may go for 1Ghz, see if she's stable.
 
Last edited:

Doward

macrumors 6502a
Original poster
Feb 21, 2013
526
8
Much obliged, sir! Freebie system needs a little Leopard breathed into it. QUOTE]

I imagine you know this, but just throwing out there on the off chance you don't... you can still install Leopard on a 800 Mhz iMac G4... without overclocking to reach the 867 cutoff. LeopardAssist to the rescue!

http://leopardassist.sourceforge.net/supported.html

Anyway, good luck with your project
Certainly, but where's the fun in that? Going to see if I can push this little 800Mhz up to 1Ghz. A 25% increase in speed would be nice :)
 

666sheep

macrumors 68040
Dec 7, 2009
3,623
211
Poland
Very interesting. Cleaned the CPU, and I've got an XPC7451 800Mhz - not an XPC 7450 800Mhz. Wonder if 1Ghz might be in the cards ;) Also noticed I do have two points that the heatsink interfaces with the casing (dual heat pipes).

I may go for 1Ghz, see if she's stable.
There's no substantial difference between 7450 and 7451. Only some bugs were fixed. Check this out if you're interested: http://www.freescale.com/files/32bit/doc/errata/MPC7450CE.pdf
1 GHz is no go, I'm afraid, I've tried... 900 was stable on few, unstable on other ones (about 60/40).
Motorola/Freescale has never clocked 7451 higher than 867 MHz. But there is a small headroom as usual.
 

Doward

macrumors 6502a
Original poster
Feb 21, 2013
526
8
There's no substantial difference between 7450 and 7451. Only some bugs were fixed. Check this out if you're interested: http://www.freescale.com/files/32bit/doc/errata/MPC7450CE.pdf
1 GHz is no go, I'm afraid, I've tried... 900 was stable on few, unstable on other ones (about 60/40).
Motorola/Freescale has never clocked 7451 higher than 867 MHz. But there is a small headroom as usual.
Interesting. I thought the 7451 was part of the 'Apollo 6' family (ala 7455, etc) while the 7450 was Voyager?
 

MaxHeap

macrumors member
Mar 28, 2012
52
0
Missouri
On any G4 overclock, do you actually have to use the resistors or would jumping it with just solder work? Have a 867 MHz Quicksilver I may want to perform surgery on. :)
 

666sheep

macrumors 68040
Dec 7, 2009
3,623
211
Poland
On any G4 overclock, do you actually have to use the resistors or would jumping it with just solder work? Have a 867 MHz Quicksilver I may want to perform surgery on. :)
Jumping with solder works well. Resistor isn't a must.
 

Doward

macrumors 6502a
Original poster
Feb 21, 2013
526
8
Correct, or you can use a thin strand wire and solder both sides of it down. :)
 

g4dg3t

macrumors newbie
Feb 12, 2014
1
0
Any luck overclocking your iMac G4? i have an 800mhz one that i was thinking about trying. I'm a little weary about bringing a soldering iron to it. i hear that going from 800 to 900 has only a 60/40 chance of being stable. Please post your results when you try it :)
 

Hughmac

macrumors demi-god
Feb 4, 2012
3,589
12,755
Kent, UK
Correct, or you can use a thin strand wire and solder both sides of it down. :)
Or, you can use conductive paint (such as is used to repair rear screen heater elements in cars).
Use a pin and magnifying glass to apply it, and make sure it's dry before firing the Mac up.

Cheers :)

Hugh

PS I must be one of the lucky ones, I've done a Pismo 400 to 450 and a Pismo 500 to 550 (both stable), using the above method.