PowerBook 5300 FAQ - A.1.1) Overclocking: Resistors

The bus-to-cpu ratio (or multiplier) is used by many PowerPC based Macintoshes to determine how fast the CPU should run. The CPU takes a sample of the computer's bus speed, then uses the multiplier to set its own speed. The multiplier on PowerBook 5300, like many other Macs (see Marc Schrier's wonderful clock chipping website), is determined by a matrix of resistors on the motherboard. These resistors are not documented by Apple, and it often takes some doing to figure it out.

The 5300/100 (5300, 5300cs, and 5300c) has a bus-to-cpu ratio of 1:3 (or a multiplier of 3x). That means that a 33.3MHz bus (which is standard on all 5300s) yields a 100MHz (ok, 99.9MHz) CPU.

The 5300/117 (5300ce) has a bus-to-cpu ratio of 1:3.5 (or a multiplier of 3.5x). Thus a 33MHz bus yields a 117MHz CPU.

The resistors that determine the multiplier are at positions R43, R46, R47, R48, R50, R127, R128, and R129 on the motherboard. The table below details the resistor settings for various multipliers.

Resistor Position:	R43	R46	R47	R48	R50	R127	R128	R129
83MHz (2.5x)	? (Resistor positions as yet undetermined)
100MHz (3x)	X	-	X	X	-	-	-	X
117MHz (3.5x)	-	X	X	-	-	X	-	X
133MHz (4x)	? (Resistor positions as yet undetermined)
In this case, an "X" indicates that a resistor _is_ installed at that location. That would mean that the resistors on Mad Dog's site match up w/ the 5300 series in a fashion something like this: (R9,R2)=(R50,R128) (R6,R5)=(R47,R129) (R8,R7)=(R43,R48) (R4,R3)=(R46,R127)

Thus, if you have a 5300/100, you can overclock it by 17% (or 17MHz depending on how you look at it) just by moving two resistors. I have done this to my 5300cs, and it is just as stable as it has ever been. The only effects I have seen are video artifacts that only appear after the PowerBook has been running for several days (I've run in this configuration for up to 14 days non-stop without problems) on end (my 5300cs has been relegated to being an ethernet/wireless bridge). The artifacts are probably a result of too much heat. While I haven't bothered to try yet, the 190 has a nice thermal pad on it's heat sink that might help dissipate more heat from the CPU if transfered to the 5300's heat sink. Also, some thermal grease on the CPU or a fan in the expansion bay module may help.

This page describes how one would overclock the PowerBook 5300 by changing the bus-to-CPU ratio.