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Upgrading to Full 68040 - Heatsink Needed?


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Yes, it is plug and play to switch an LC040 to full 040 - it's only if you want to overclock the CPU you need to perform the resistor and/or crystal swap.

 

And wrong CPU, as in speed?  A 25Mhz 040 will probably drop in and run fine at 33Mhz, and a 33Mhz will down clock to 25Mhz without any adjustments.

Edited by Byrd
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Ok, not sure what anyone is saying. The plan was to swap the stock cpu on my LC 575 with this:

 

http://m.ebay.com/itm/111633589714?euid=53fb61ae6fb34856a8be059ee404075d&_mwBanner=1

 

But I'm assuming that since my stock runs at 33mhz, and the one I bought runs at 33mhz, there's probably little point in doing so, correct?

Edited by Guybrush3pwood
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I bought one from the same seller and did the upgrade on the same logic board as you did. Applications that take advantage of the full 68040's floating point unit will be dramatically faster than with the original 68LC040 processor. On the LC version, floating point operations are emulated in software, which can take 10-20x as long. Non floating point operations will run about the same. Some software requires a floating point unit and will not run on your original 68LC040.

 

As for frequency, hardware on the logic board, not the processor determines the speed. If you found a 40MHz 68040, it would run at 33MHz unless you modify your logic board (as per the links others have posted.)

 

In short, you bought the right processor for your machine. Some applications will be hugely faster, others will be the same. Given the mask codes the seller has, a heatsink is not mandatory, but is a good idea.

Edited by rsolberg
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The speed of the processor is determined by the logic board... there is no such thing as a "33/40MHz 68040". Although, 68040's can have different masks (the coolest being "L88M") which make them run cooler, and more stable.

Edited by Floofies
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max out the memory and the cpu to a full 68040 for the fpu will help, but if you can boost cpu speed from the link i put up the 25 mhm to 33 mhz is big, and so is 33 to 40 mhz.  I took my 638CD to 40 mhz and its faster than I ever remember and with the full fpu everything is quicker.

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Older m68040s, which are labelled "XC", require heat sinks for speeds faster than 25 MHz and really should have a heat sink for 25 MHz. They're fine at 20 MHz. They are made with a 0.8 um process.

 

Later m68040s, labelled "MC", use a newer and smaller mask (0.65 um) and therefore take less power. They're usually fine at 25 without a heat sink but should have one at 33 MHz or faster.

 

The last m68040s, which have masks K63H or L88M, use a .057 um process and run coolest. They can be run at 40 MHz without a heat sink and run reliably at 50 MHz with a heat sink.

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Most original m68040s can run up to 40 MHz without problems because they're all made the same - the chips labelled 40 MHz from Motorola were tested and confirmed good at 40 MHz, but internally they're no different than the 25 and 33 MHz parts. Some of them, when properly cooled, can run up to 50 MHz.

 

The 0.65 and 0.57 um (typo above - it's 0.57, not .057) masks can pretty much all run at 50 MHz with proper cooling. I'm running a few early XC chips in NewerTech Quadra Overdrives at 50 MHz and got a K63H mask chip for one of them, and it runs fine without a heat sink but with a small fan at 50 MHz.

 

Therefore, I think overclocking a newer mask is more or less limited by the rest of the system, not by the chip itself.

Edited by johnklos
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OK, thanks.  I have a Daystar Turbo 040 with a 40MHz rated MC68040RC40 with the .65 mask.  It already has a heatsink, but I think I'm going to remove it, apply some thermal grease, then put a new heatsink and a fan on it.  I'd like to get 50MHz on it. :)

 

The Turbo 040 has a lot of extra electronics, so I'm hoping it won't suffer the same issues as simply overclocking the CPU directly on the motherboard.  Not sure what the terminology is for that.  Separate CPU clock from the BUS clock?

Edited by olePigeon
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