Overclocking GVP Combo 040

Hey guys.

Now that I have this running rock solid stable (weird gfx corruption and instability problem was caused by icons being stored in Other Memory instead of Chip), I would like to overclock it! :)

Not by much mind, it is currently running at 33mhz, I would like to knock that up to 40. Now I already have some 40mhz 68040s (XC68040RC40M), so even though a modest overclock from 33 to 40 would probably be quite stable with the old 33mhz, I thought I may as well replace it with a faster part to be safe.

The Combo 040 has a socketed cpu, so just a quick swap there. And the clock crystal is also socketted, so can anyone see any problems with swapping the cpu and clock crystal to knock it up to 40 mhz?

Search for a MC68040 part: they don't heat much and are better on faster clocks.

Hey there,

yessum, the MC series is always preferred, but if I only go to 40 mhz, surely heat wont be a big problem - since that is what the XC is rated for (40 mhz)?

I have an Apollo 1240/40 (too bad it have the 130 MACH chips...), it does not heat insanely as it's other slower brothers.

I think it is because Motorola tested the CPU one-by-one and labelled them accordingly to the clock they can work for an intense burn-in-test.

More: I think the "burn-in-test" concept was created by Motorola because this very CPU, LOL.

Okiez, I have now replaced the XC68030RC33E (whats the E stand for?) with an XC68040RC40M (erm, and the M - what does it stand for???), glued on a heatsink with some nice artic silver....

....and it boots and runs still (I never doubted it for a minute)! Of course, it is still only running at 33 mhz atm, but Im letting it "burn in" the heat transfer compound by endlessly running a doom II demo via Adoom (give the cpu a good work out).

Have ordered a 20 mhz crystal, it should be here mid next week, will post the results running at 40 mhz.

I suspect it will run flawlessly, and I can probably kick it up to about 46 mhz. The GVP Combo 040 came in three flavours - 25mhz, 33mhz and 40mhz, and from I can see, the only difference between them was the cpu and clock crystal. All other hardware, controller chips etc are identical, so if the 40mhz version of the board can run at 40 mhz with a 40 mhz 040 installed.... by replacing the 33mhz 040 on this 33mhz board with a 40 mhz 040 and matching crystal, I have essentially turned this GVP Combo 040 33mhz version into the 40 mhz version - until I go OVER 40 mhz I am not really overclocking anything.

Anywho, will be interesting to see if it will go up to say 46 mhz (I believe if you go much over this that the controller/logic chips will start to malfunction and cause stability problems long before the cpu does).

XC= not a fully qualified part / Engineering sample / Pilot production device
RC= Ceramic PGA, gold lead finish
E or M = Processor revision

Thanks LTac - tell me, which is the best revision out of E and M?

M are from MC parts only.

Read this:
http://eab.abime.net/showpost.php?p=745447&postcount=7
http://eab.abime.net/showthread.php?t=51276

Quote:

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Originally Posted by abraXXious

Have ordered a 20 mhz crystal, it should be here mid next week, will post the results running at 40 mhz.

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Im a bit confused by this line.

And further, I beleive the 040 halves the clock frequency, ie: 80mhz xtal will result in the CPU running at 40mhz.