Part I: Underclocking a PowerBook 1400/166 Processor Module

To run in a PowerBook 1400/117


 | Go to Part II |


The PowerBook 1400 series is getting antiquated by today's standards. I use a 166 MHz model for e-mail, when I travel and at home, for browsing, sometimes. My wife has the 117 MHz model. Due to the lack of an L2 cache, this sorry PowerBook is excruciatingly painfully slow. It seems slower than the 68k Mac Quadras are. I have to wonder how many people upgraded from the 500 series PowerBooks and wondered what all the PowerPC fuss was about? You can upgrade the PB 1400/117 to 133 MHz with the processor module from a 133 MHz 1400 and get an L2 cache in the bargain but the ROMs prevent using the 166 MHz version. As luck would have it, I had a spare 166 MHz module collecting dust until I found this page. The author suggested that it may be possible to underclock a 166 MHz module to run at 133 MHz in a PB 1400/117.

After getting my wife's consent, the first bit of information I was going to need, was the location of the resistors on a stock 133 MHz module. I found that information here. It was then a matter of rearranging the resistors on the 166 MHz module to be like the 133 MHz version. NOTE: The following is offered for informational purposes only. Any modifications you attempt, are soley at your own risk.


Resistor Locations:

133 MHz Module

166 MHz Module



0 Ohm jumper (0)



10k Ohms (103)


1k Ohm (102)




100k Ohms (104)


0 Ohm jumper (0)



Original Location R5 R22 Location

After removing the clip from the end of the heatsink and carefully bending the end up, the resistor at R5 must be unsoldered and moved to R103, on the other side of the board. Bend the heatsink back down and re-clip it before doing any soldering on the reverse side. The resistors at R20 and R22 must be removed and a 1k Ohm (102) resistor must be soldered at location R21. As you can see in the photo, I scrounged a large 1k Ohm resistor from another source (a dead 7100/66 mother board, location R313, if that helps).

Locations R103, R21, R20 Soldered at R103 & R21

After substituting the underclocked 166 MHz module for the original 117 MHz one, The 1400 booted and reported the following:

PowerPC 603ev at 133 MHz

If you are thinking that it may be possible to reverse these instructions and overclock a 133 MHz 1400 to 166 MHz, the ROMs in your 1400/133 may prevent it. If you try it and it works, please let me know.


Part II: Overclocking a PowerBook 1400/117 Bus

to Make its Underclocked 166 MHz Processor run at 160 MHz


Now I had a 117 MHz 1400 running at 133 MHz. I also knew that I could overclock the bus to anything I wanted and the ROMs wouldn't stop me. They were only concerned about the gestalt ID according to the way the processor was arranged. The underclocked 166 MHz processor had them fooled into believing that this was a legitimate configuration. All I had to do now was replace the 33.3333 MHz oscillator with a faster one, in this case 40 MHz. The 1400/117 should run at 160 MHz (or 4 x the bus speed), the ROMs should be happy and there should be absolutely no long term risk to the processor. It would still be running slightly below its specs. Unfortunately, I couldn't find a source for a 41.5 MHz oscillator which would have provided 166 MHz.

I started by reviewing the information on the previously mentioned page. The author explained how to overclock the bus and provided a source for the 40 MHz oscillator (part # SE2851CT-ND Mind his cautions! As with the above procedure, this is a tricky soldering job. When I had the 33.3333 MHz oscillator replaced with a 40 MHz one, I reassembled the PowerBook and booted it. Note: If the sleep light at the upper right of the 1400 screen is glowing steadily after reassembly, you must reset the Power Manager by holding and releasing the button in the back of your 1400 (details in the manual). Since the gestalt ID does not change from the 133 MHz configuration, Apple System Profiler will report that the 160 MHz 1400 is running at 133 MHz. You will need another utility that actually measures the speed, to give the real picture. Here is what Gauge Pro reported:

1400/117 at 160 MHz

With 166 MHz processor modules showing up on eBay regularly, this is a great way to get a major speed boost in your 117 MHz 1400. It does take some skill and time. The best part is, there is no stress on the processor since it is running slightly below the intended speed. As always, the risk involved is all yours. You may damage your PowerBook by following these directions. If you break it, it is entirely your own fault. Have fun!

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