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Mac SE/30 processor question.
Posted by: michelbites on 2016-12-21 12:34:17
Someone was telling me that I might be able to upgrade my MC68030RP16B processor to a MC68030RC50 or a MC68030RC40 just by swapping it out. Is this true. Would this do any damage to the board? I would like to hear peoples thoughts. These are the processors that I found that are in the same line as the one in my SE/30. Thanks. http://www.cpu-world.com/CPUs/68030/Motorola-MC68030RP16%20-%20MC68030RP16B.html
Posted by: joethezombie on 2016-12-21 12:59:20
You can replace them, but you would get no performance increase by doing so.  The clock will still be locked around 16MHz-ish regardless of the speed the processor is rated at.  You could try to swap the oscillator with a higher frequency version, but I would imagine it would cause all kinds of severe problems with the other onboard systems, which all gather their timing from the same oscillator.  I remember reading one such individual achieving a stable 20MHz bus, but that's a lot of work for such few MHzes.

This is why the SE/30 accelerators are so sought after, and why Artmix can sell a simple adapter for $200.oo.  
Posted by: ZaneKaminski on 2016-12-21 14:14:51
I have wondered about this. The main limiting factors on the clock speed achievable with a faster oscillator are the maximum speeds of the 68030, Apple "GLU" chip, the asynchronous DRAM latency, and the peripherals.

The processor and DRAM can be upgraded to higher speed grades, but the peripherals, VRAM, and GLU, I'm not sure. Maybe they will work at 20 MHz, but maybe they will not work or be unreliable in a certain way.

Buuuuuut, there is one more problem. The Mac II series is more easily overclocked than the compacts, because the Mac II series have separate video and processor oscillators. But the compacts, including SE/30, use the same oscillator to drive the video circuitry and the CPU. So increasing the frequency would do weird things to the video. It may be possible to modify the SE/30 by cutting the clock trace to the video circuitry and adding another, slower crystal oscillator to feed the video output.

So to summarize:

  • Upgrade CPU, DRAM and VRAM to lower latency
  • Ensure peripherals and GLU will work at the higher speed
  • Cut the clock trace to the video system and send it a clock speed matching the original video clock (either 15.6672 MHz or 31.3344 MHz, not sure)
  • Replace stock 33.1144 MHz crystal oscillator with higher frequency
Posted by: michelbites on 2016-12-21 16:44:53
Thank you for your answer guys. I always wondered about this.
Posted by: unity on 2016-12-21 18:05:24
Zane is right. I think this may have been attempted before but there were video issues. In the end, if there was an easier way it would have been done commercially instead of using upgrade cards. Of course the cards usually require the socketed version of the board which is not every one.
Posted by: ZaneKaminski on 2016-12-23 10:55:23
Commercial products basically can't involve out-of-spec operation of chips, so naturally nobody sold upgrades of this type. (Though some companies did seemingly certify 40 MHz 68030s to run at 50 MHz.)

But for someone with some technican's skills, it wouldn't be too hard of a project, I don't think. The hard part is finding and cutting the "C16M" 15.6672 MHz clock signal going to the video circuitry and wiring up another oscillator to it, separating it from the rest of the machine to be overclocked.

Of course, there's a high probability of destroying the SE/30, at least beyond anyone's capability to repair, and it might just turn out that the mod won't work at all.

Also if the GLU chip and other peripherals can't run at 20 MHz, you could try increasing the voltage from 5V to 5.5V or 6V. Obviously you don't want to crank it up too much, but that extra voltage might reduce the propagation delays in the chips that limit their performance to ~16 MHz.
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