Overclocking the 680x0 of the BlizzardPPC board is quite simple. The hardest part
to do is to find a replacement oscillator for the 50Mhz supplied. All you need to
overclock the 68k is a brand new oscillator, rated at 60 or pure 66Mhz. When you'll find
the crystal, you are half done.
Overclock the 68040/68040EC: As many of you probably know, the 040 speed is
determined by a multiplier factor of 1:0,5. This means that if you have a 50Mhz board,
like the one supplied for the BlizzardPPC boards, the 040 will be clocked at 25Mhz.
A 60Mhz crystal will of course give 30Mhz, while a 66Mhz one will give 33Mhz. Finally,
80Mhz are used for 40Mhz. How far can we go? There isn't a true answer to this question. Clocking the 040 to
30Mhz is quite safe, the cpu doesn't get much hotter (yes, it is hot by default, but don't worry much about
it), at 33Mhz too the overclock runs stable. Remember to use a good heat sink, maybe with a nice
fan on it. I suggest, if you can find one, to use the heatsink from the a3640 (the A4000 CPU card),
it is big, fits perfectly and is really the best heatsink for 68k, better than the Pentium/AMD ones.
I am using the 040 clocked at 33Mhz with this heatsink and no fan for months, and I have no problem at all.
A warn if you want to try 80Mhz: I've benn reported that this overclock works, but I am quite doubtful
about its safeness. I don't think that a 25Mhz can handle such an overclock for much time, so do it at
your own risk, maybe it works, but no one can tell you if it will work for years.
How can we do it?: It's simple. Assumed that you have a 60, 66mhz crystal, warm your soldering
iron, and gently remove the 68k crystal warming on the pins that you see on the lower side of the board.
BE CAREFUL! Under the crystal there's a little chip, so beware! If you damage it you can break your card, and
it won't work again. The 68k crystal is simple to locate: seee the picture, it's a 50Mhz one (you can read on it).
If you have two 50Mhz (rare!), the needed is the "inner" one, not the other near the edge of the board.
After you can plug the new crystal and solder it, taking care not to push it too much or it will
come too near to the chip.
Overclock the 68060: The story is the same for the 040, the crystal is the same, and also the frequency
you have to look for. The only thing you should care is that the multiplier factor of the 060 is 1:1, so if the
60Mhz oscillator is used, also the 060 will have 60Mhz. A very good overclock is to 66Mhz, the 060 doesn't get
too hot (remember that it's a low voltage chip, 3.3V instead of the 5V used i.e. for the 040), the performance
gain is great, and the stability is perfect. Don't forget, to be safe at 100%, to use a good heatsink and/or
a fan.
Notes about the memory: Since to overclock the CPU we have to up the frequency of the bus, you have to make
sure that your ram SIMM can handle higher bus speeds. In some cases, if you have very bad modules,
you may need, from the BlizzardPPC bootmenu, to lower some settings of the RAM for the 68k , rating your RAM at 70ns or
activating the 68k preload or precharge. Do some tests to find the optimal values. If you can deactivate all the precharges
and the preloads, you have very good memory.
Notes about the sockets: It is very useful, if you want to switch crystal depending on your need or simply just to have
the possibility to do some tests without using always the soldering iron, to mount a socket for the oscillator.
You can find it (sold in rows) in every electronic shop. If the sockets are like the one in the photo, you have to cut the inner
pins from the base, and solder just the 4 ones in the holes for the oscillator.
