Switching processors between 520 & 540c

[CC_333]

How about both?  A full 68040 overclocked?

True point. The thing is, though, that to me knowledge, LC040s of any speed are easier, and thus cheaper, to come by these days than full 040s, particularly in the form factor needed for the 540's CPU card.

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[Cory5412]

In that case, my logic tells me that a faster LC040 running at, say, 40 MHz, is more beneficial than a full 040 running at the stock 33 MHz or 25 MHz, yes?

It depends on what you're doing.

Truth be told, I have yet to see significant evidence that most people are doing high end work with their vintage Macs, so for most people, a 40MHz 'LC040 would be more beneficial than a 33MHz Full040.

How about both?  A full 68040 overclocked?

The only real need for this is typically bragging rights. The handful of people I know doing work on their upgraded or overclocked '040s don't post about it for the sake of bragging that they have, of all things, an FPU, or that they've managed an overclock.

particularly in the form factor needed for the 540's CPU card.

This is the real kicker for this particular thread - it's not like we're talking about an 800/850/950 here.

The biggest gotcha, of course, is that of course the PowerBook 550 did have a full 040, and I don't know if there are any heat differences between the full and "LC" versions of the 040. If not, then it doesn't really matter, and any given form factor either "can" or "can't" cool an 040 at a given speed, regardless of what type it is. (but, again, that depends.)

 

[Paralel]

Yup, just to say I did, that fits. 

That's the ethos I work from.

As far as trying to install a faster LC040 in a 540. You'd need to implement some kind of cooling solutions, such as a low profile heatsink, similar to what is seen on some of the PPC upgrade cards for the 540, because the full 040 @ 33 MHz is known to cause the 540/550 to exceed its thermal budged and lock up on hot days, because it is borderline with the sad cooling solution in the 540/550. I doubt it would tolerate an LC040 at a higher speed very well.

Also, I don't think they ever made an LC040 @ 40 Mhz QFP. I've only ever seen a full 68040 in PGA format. 

Edit: From looking through NXP's site, they did indeed make a 68040 @ 40 MHz QFP, but only in the full 68040, no LC, so no doubt it would indeed exceed the thermal budget of the 540. You'd need a cooling solution for sure.

 

[Paralel]

I found the reason why there were never any attempts to make 68040 @ 40 Mhz QFP upgrade for the 500 series at that time, the part didn't exist. From what I can tell reading NXP erratum, the QFP format for the 40 MHz part didn't exist until the 21st century at Freescale when they moved the 68040 (at that time meant for embedded applications) to a newer fab process. 

Technically, it should be pretty simple to implement this type of upgrade now. Just make sure you have the right crystal, and that should be all you need.

I'll leave this to someone else though, from what I can tell doing a quick search, people are asking ~$380 for a MC68040FE40A. Too rich for my blood.

 

[jessenator]

Even with a heatsink, the 040 on my DayStsr even idle gets HOT. Granted it's OCd from 33 to 40 via oscillator, but even with the passive arrangement it's toasty. I might check it with an IR thermometer out of curiosity.

Definitely got hotter than my Q610 ever did.