I managed to speed bump my PM4400/200 to 240MHz. Turns out the answer was written on the silkscreen of the Motorola StarMax! You can set the speed to anything between 80MHz and 240MHz (in mostly 20MHz steps).

I got an 11% improvement in Norton System Info's CPU benchmark overall (from Norton Utils 6). The limitation is that RAM doesn't change speed so the RAM heavy benchmarks don't see the full 20% increase. See the breakdown.

Should work with the various Tanzania Motorola StarMax, Power Computing PowerCurve, UMAX/SuperMac C500 C600 machines as well as Apple's 4400 / 7220. Assuming you're not already running at 240MHz.

My CPU runs cool enough to comfortably leave my finger on the centre of the heatsink and I left it running at 240MHz for about an hour (I stopped restarted to benchmark back at 200MHz).

Instructions are available here if anyone wants a go - basic soldering skills required, but nothing fancy. Basically if you can solder a standard 2.54mm header and clear out solder flooded through holes.

Thanks so much for posting this, I've previously looked at those "CPU Option" pads and wondered.

Have you seen the thread on the MLA forum about modifying Alchemy (5400/6400) logic boards for 50MHz bus speed?

The gist is there is more to it than just the crystal oscillator. I got this working on a 6360 board however none of my L2 cache modules would work (including those from a 6500 that def should function at 50Mhz).

>> Fizzbinn said:

Thanks so much for posting this, I've previously looked at those "CPU Option" pads and wondered. Have you seen the thread on the MLA forum about modifying Alchemy (5400/6400) logic boards for 50MHz bus speed? Found the 50MHz bus switch on Alchemy (5400/6400) tl;dr: Remove R95 and install R94 (10k ohm 0603) to configure the PSX chip for 50MHz operation. Full story: I picked up one of my dream Macs a couple of weeks ago, a 5400/200. I met up with @dv- at Free Geek Twin Cities to collect it and return his battery-bombed Q650 motherboard I repaired... 68kmla.org The gist is there is more to it than just the crystal oscillator. I got this working on a 6360 board however none of my L2 cache modules would work (including those from a 6500 that def should function at 50Mhz). Click to expand...

I hadn't, but I had come around to the same information via another route. I have the schematics they're talking about for the 6500 so I can double check things and make sure it matches what I'm seeing on the 4400.

I've ordered an SMD 50MHz crystal, it takes longer to dismantle the machine than to swap the resistor (if needed) and change out the clock. I might be able to reach both without taking the board out of the case to be honest, that would save me a bit of time and a blood sacrifice to the god of pressed metal cases.