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Upgrading to Full 68040 - Heatsink Needed?


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Unless you have a different logic board in your 6115CD, you'll find it already has a 60MHz PPC 601 with integrated FPU soldered to the board. As for the two 575s, it's strongly recommended to run full '040s with heatsinks as they produce significantly more heat than the LC040 they'll be replacing. Some very late examples of the 68040 have improved thermal characteristics and run well without. I run an MC68040 with mask code L88M and it runs barely warm to the touch without a heatsink. That mask was only introduced in 2002, though. The previous revision introduced in 2000, the K63H will probably be fine without too. Any XC68040 is earlier and needs a heatsink. An MC68040 with mask code E42k will probably require a heatsink.

 

See here:

http://newsgroups.derkeiler.com/Archive/Comp/comp.sys.m68k/2006-01/msg00000.html

 

EDIT: Mr Pippy, your Quadra or Centris 660 ran at 25MHz where the OP's 575s will run at 33MHz. The full 040s get very toasty at the higher frequency. Unlike an Intel 486SX and DX, where Intel disabled the FPU for the SX models, the 68LC040 and 68040 are distinct designs. The full 040 has far more transistors on die due to the fpu, which leads to far more heat.

Edited by rsolberg
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Thanks for the info, that all makes sense. I have a Q605 and a Mystic CC, and a full 040 I want to put in one of them at some point.

I just took a look at the Quadra 650 and 840AV logic boards, both with 33 MHz 040s, and they both have heatsinks.

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well it depends… if you are running the cpu @33mhz and not over clocking it in your lc475 and you get ahold of a quadra 840av cpu witch is 40mhz cpu.  i would say you could use it with out a heatsink.

 

however if you put a 25mhz Quadra 630 or q700 full cpu in there… and are running it at 33mhz yes absolutely you need a heatsink.

if you found a full 33mhz cpu from a q800, i would still heatsink it.

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Mirroring what Uni said here, the 68040 doesn't require a heatsink unless you run it at or above 33Mhz.

 

So were heatsinks ever made for the full 040? I searched ebay but didn't find anything.

Your 68040 uses a PGA-179 socket, so get a heatsink for that socket. Or measure the processor and find a stick-on heatsink of the same size. Or, you can order several smaller heatsinks that geometrically fit on top of the processor.

Edited by Floofies
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You definitely don't need a fan on the processor. The chip is around 47x47mm, so  something like this would work fine.

 

Funnily enough, I've seen a few clueless Q/A sites recommending HUGE heatsinks like this for a 68040. Really made me laugh!

 

By the way, I recently accidentally ordered a few extra heatsinks for the Valkyrie chip. If you want one (or a few) and can pay the cheap shipping/mailing cost, I can send some to you.

Edited by Floofies
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Either by adjusting the multiplier of the CPU by adjusting some (small) resistors on the motherboard, or adjusting the frequency of the CPU by replacing the clock crystal - all models differ.

 

I've used GPU, 486, northbridge heatsinks on my '040 CPUs to great effect - doesn't need much (if anything), but the cooler the better in these old dears.

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