Powerbook G4 550Mhz 100 to 133Mhz Bus

---

Step 2

Circuit Area Identification :

• Find the set of surface mount resistors in the center of the circuit board. (unit face down with I/O ports away from you)
• There will be a group of resistors located near the bottom case screw stud post to the left of the Airport Card socket.
• There are two parallel rows of resistors between inductor Y5 and capacitor C689.
• Changes will be made to the components in between these two rows and in the bottom row.

Step 3

Resistor Installation/Move :

This part of the procedure is where soldering skills are essential. It will take a steady hand and VERY careful use of a soldering iron. We use a special soldering 'tweezer' to lift the resistor and move it to the new location. Flux might make this easier for pencil type soldering irons. Three special precautions: 1.) Don't loiter with the soldering iron on the main logic board - cook it and your board is toast!, 2.) Accidentally fracture the resistor and, uhh... your board is toast, 3.) Drag the iron or overheat it and lift a trace and - you guessed it, your board is toast.

• On a 550/100Mhz a jumper is installed at location R126.
• On a 550/133Mhz a jumper is installed at location R661.
• On a 550/133Mhz a jumper is installed at location R662.
• Picture 4 shows a 550/100Mhz before the changes. Picture 5 shows the jumpers, after the move, installed at location R661 and R662(550/100Mhz)
• * All you have to do to change a 550/100Mhz machine into a 550/133Mhz machine is to move the jumper from R126 to R661 and install a jumper/solder bridge at location R662.

Step 4

Pre-Assembly testing :

• Test boot the machine by reinstalling battery or connecting AC adapter.
• Use your favorite utility, such as Gauge Pro, to confirm bus speed change was effective.
• Be aware of the open traces on the back of the unit - don't set the unit down on your workbench, screws, tools, etc. Lay unit on its side to protect the main logic board.
• Reassemble machine using reverse procedures. 

Conclusion
When Apple released the 550 and 667Mhz models we were hoping for some great performance improvements. As it turns out, these machines weren't so hot. In fact, we actually found better performance(for some functions) with the Powerbook 550Mhz we speed bumped(from 400Mhz)...which was kind of a disappointment.

While the procedure listed here initially gave us some grief(the settings for Bus and Processor were tough to reverse engineer, we couldn't initially figure out the processor speed settings and we didn't have much free time to work on it), we believe it to be an accurate method of bumping the bus speed from 100Mhz to 133Mhz. Most of our work is the result of careful comparison between a stock 550/100Mhz and a stock 667/133Mhz ...NOT an in depth understanding of the config circuitry Apple used in the design of these machines. The resultant bus speed indicated by most utility software is still a bit puzzling(they do not show a clean "133Mhz" figure...).

We've included an email address below if you have further information to contribute, but please don't expect a response - and please don't ask us to fix your machine if you break it(Although, if you're really in a bind we'll take a look at it -but we're an Apple Authorized Service Provider so don't expect us to cover a fix under warranty!).

Rich Voelker, Voelker Research
Michael Kimbrell, Service Coordinator

Want to relay your results?

---

1/29/02 - 6:10pm MST First machine bus bumped. Has been running without issue since the changes.
5/1/01 - 10:15pm MST Smoked a stock 550Mhz MLB while shooting pictures for site. (Lesson 1: DON'T work on the machine when the battery is installed!! ...put the beer down ...remove the battery. Follow the procedure.) Repaired board, procedure applied, machine works good.
5/8/02 - 9:15am MST Discovered additional information that may reveal the technique for processor speed bump from 550Mhz - > 667Mhz. More details to come shortly...