Dinsdale Piranha wrote,

A weird idea just occurred to me (what can I say; tis the wee hours) which
I'm almost positive is completely ridiculous, but I figured I'd bring it up
here because, well, the lot of ye are the only people I can think of
offhand who might know.  :)

I have a IIcx here, with the pokey 16MHz 030 (runs NetBSD a hell of a lot
more efficiently than MacOS, of course). I was wondering if anyone
thinks it might be possible to rip out the 16MHz chip (it's probably
soldered in, but that's another story) and replace it with another 030, say
a 25MHz or 33 or something.

As I said, I'm sure there are a *thousand* reasons why this could *never* 
work and is an incredibly silly notion to begin with, but...if anyone can
tell me, I'd be interested to know why.  I'm guessing any number of things
involving clock speed, bus speed, etc.  But on the other hand, I'm thinking
the pinouts and instruction sets for two 030's of different speeds have
gotta be exactly the same...

This wouldn't work because the chip would still be clocked by 16MHz instead of 25MHz. 
One thing that MAY work on the IIcx is replacing the christal oscillator by a faster 
one and replacing the 030 by a version capable of higher speeds. BUT this will only 
work if the motherboard is also capable of handling the higher speed. This way I 
upgraded my LCIII from 25Mhz to 33MHz. This works because the LCIII is underrated 
at 25MHz.
For the IIcx this may require some soldering to the circuit board though, which is 
something you may not want to do unless you are very confident that the upgrade will 
work.

regards,

Robert.