Overclocking Apollo 1240/40 to 50MHz?

[tomekm]

I am looking for info on the following topic:
Is the Apollo 1240 able to drive 68040rc40 at 50MHz i f I replace the oscillator with 100MHz one? I know the 040 itself should handle it. Especially if my one does not generate much heat (Pentium 1 and little fan driven by thermistor is much more than enough).

Does anyone know if it works and does anyone have 100MHz oscillator to sell?

[PMC]

It depends on a lot of things...  If the CPU is a rc model, then it's ceramic coated which makes it better at conducting heat.  Is the CPU relatively new?  The older the CPU generally the less tolerant to overclocking it will be.

40Mhz is the upper design limit for an '040.  I managed to safely and successfully overclock my 25Mhz unit to that speed, but it wouldn't go any further.  

If I were you I'd either invest in an '060 accelerator or if you are determined to overclock I'd suggest going in steady increments of say 2Mhz over and above the rated speed.

You might see Mac '040s advertised as being 50Mhz units.  This is because as you know the processor cycles every second clock pulse.  I don't know of anyone getting more than 44-45Mhz out of an '040 but you can always try...

[TjLaZer]

On a side thought, I have a Apollo 1240 25MHz and I swapped the Oscilator and am running it at 33MHz no problems at all.  Not sure about the 40Mhz model though, but since 040s run so darn hot it probably would be a bad idea, especially in a desktop A1200.

[PMC]

@Tj

It's not just heat, it's current too.  You'll need to source a pokey PSU to supply the required juice for the A1200, HDD (required to load an os containing '040 specific libraries), CPU and extra memory.  

The A500's stock PSU struggled on my 25Mhz system.

On the plus side, my 25Mhz '040 was fitted with a heatsink between the fan and surface of the chip and ran happily at 40Mhz without problem.  I tried maxing it to 50Mhz, but all I got was a black screen, but the system was none the worse after being reset to 40Mhz again.

[tomekm]

ok, let`s verify some things:

-afaik the fastest version of 040 is 50MHz.

-My 040 is the RC revision.

-My 040 DOES GENERATE MUCH HEAT, it is cooled by Socket7 lowprofile radiator and 486 fan, driven by a thermistor. It is far more than enough. I remember one time I forgot to give the voltage to fan. The computer hung up after 5 hours of hard work (DigiBoosterPro)...

-My A1200 is fitted in BIG tower.

-My PSU is 250W.

-The fan voltage is not taken from Apollo, instead directly  from PSU.

Seems that overclocking should be possible, but I have no oscillator to check, and don`t want to buy one until I`m sure it`ll work because they`re too expensive (and unavailable in my city).

 

[PMC]

tomekm wrote:
ok, let`s verify some things:

-afaik the fastest version of 040 is 50MHz.

-My 040 is the RC revision.

No, the fastest version of the '040 is 40Mhz.  Some Mac expansions were shown as beiing 50Mhz becuase the 25Mhz 68040 needs a 50Mhz oscillator as it's timed to cycle on every second oscillator pulse.  If you check your CPU you will find that an 80Mhz oscillator is fitted, thus giving 40Mhz chip speed.

Seeing as your system is in a tower with a fan and a pokey PSU, you have scope to dissipate the heat and power your system.  However, running an '040 reliably at speeds higher than 40Mhz is difficult because it's right at the limit of the design capability.  It's up to you, but I wouldn't take it beyond 44Mhz.  To try and run it at 50Mhz is asking it for more than a 20% increase in speed which is likely to be more than your '040 can handle.  

At best, you'll have paid for a 100 Mhz oscillator and be greeted with a black screen on bootup.  At worst, your CPU will destroy itself, possibly taking the accelerator card and memory with it.  

[tomekm]

No, the fastest version of the '040 is 40Mhz.  Some Mac expansions were shown as beiing 50Mhz becuase the 25Mhz 68040 needs a 50Mhz oscillator as it's timed to cycle on every second oscillator pulse.  If you check your CPU you will find that an 80Mhz oscillator is fitted, thus giving 40Mhz chip speed.

i know that 040 uses every second cycle, altrough for I/O operations only. The processor`s arithm core runs at full speed (in my case 80MHz). That`s the reason why there are 50MHz 040 in Macs. I know it. But also I`ve seen a table of benchmark results taken from some web page which showed: 040/25, 040/33, 040/40 and 040/50. So it means that there was 50Mhz version. Also: i`ve seen old 040/25 running at 40Mhz, so  i see no reason to run 040/40 at 50.

[PMC]

Yeah, I too ran my 25Mhz '040 at 40Mhz without issue.  

Amiga Format ran an article back in 1998 when they explained the pros and cons.  They explained it a little like this.

Because the 68K series is getting quite old, normally only one set of dies is used to produce the CPU.  These are then tested at varying speeds, and rejects are quickly dumped.  These chips are pressed into the ceramic cases and the speed ratings are applied.  It's quite possible that all 68040 CPUs produced since are manufactured to 40Mhz tolerances, but down rated accordingly.

http://www.cpu-world.com/CPUs/68040/

Note that according to CPU-World, the 68040 was maxed at 40Mhz.  I've never heard of a 68040 being rated at a higher speed.

Try it by all means, but I offer no guarantees that you won't suffer system damage as a result.  

[Damion]

The fastest 68040 from Motorola is/was 40 Mhz, anything at 50 MHz is overclocked.

Website link

[Effy]

And what about the Sonnet Quaddoubler

Plug the Sonnet QuadDoubler™ processor upgrade card into a Macintosh Quadra or Centris and double your computer's speed. The QuadDoubler features a high-quality Motorola 68040 processor with FPU, ideally suited for graphic applications, spreadsheets, web browsing, and complex mathematical calculations.

Featuring a fast 100/50 MHz 68040 processor with FPU, the QuadDoubler is compatible with your existing hardware and software. A lower cost 80/40 MHz 68040 processor is used in the QuadDoubler for the Centris 610 and Workgroup Server 60/20. The QuadDoubler fully supports Mac OS 8.1, allowing you to take advantage of features and capabilities previously unavailable in the Mac

[tomekm]

OK, thank you all... I`ve got blizzardppc (which is dead now... but i`ll try to recover it.

[tomekm]

OK, thank you all... I`ve got blizzardppc (which is dead now... but i`ll try to recover it.