Upgrading your CPU - Performa 630CD and others

I'm interested in upgrading the CPU of my Performa 630CD from the LC CPU to the full-floating-point-capable functionality of the standard 68040 cpu. Also, I see there are ways to move some resistors around on the motherboard to increase the Mhz from 33 to 40. So if I did both, I could go from a 68LC040 @ 33Mhz to a 68040 @ 40Mhz!

Check out these links on the subject:
https://web.archive.org/web/20100823094417/http://homepage.mac.com:80/schrier/q630.html
(Yes, I realize that's a 575 not a 630)

So when I look on ebay for a 68040@40mhz I see there are several different model numbers of the chip. Can anyone tell me which models are compatible with the Performa 630CD logic board (assuming I can set the right resistors for the bus speed)?

Here's some model numbers I see on ebay:
MC68040RC40A NXP
MC68040LRC40A
XC68040RC40M
MC68040RC40

Tom2112 said:

Can anyone tell me which models are compatible with the Performa 630CD logic board (assuming I can set the right resistors for the bus speed)?

Here's some model numbers I see on ebay:
MC68040RC40A NXP
MC68040LRC40A
XC68040RC40M
MC68040RC40

Click to expand...

The big question is not so much 'compatible,' but 'genuine' with regard to eBay fare these days*.

Any 68040 (that isn't a late model "V"at-the-end (which is 3.3V)) PGA package will socket into am 040 Mac, as far as I'm aware. A higher-speed-rated CPU will only operate at what the logic board tells it to, hence the clock chipping (of which I'm not so secretly a fan). so a 25 Mhz configured board will still tell a 40 Mhz piece of silicon to run at 25 Mhz...

* so there were many revisions of the 68040, (masks) where it was improved upon or die-shrunk for thermal envelope. 'XC' which is found in every stock 040 Macintosh, is 'unqualified' or simply didn't meet Motorola's standards for the design (as far as I understand it). I'm not a HW engineer, so someone who is, please correct me ) so they were rated, typically for lower speeds, and had hefty heatsinks. In 1995, after Apple had already moved to PowerPC, the market finally got 'qualified' or 'MC' branded silicon. indicated by the mask— site's in German, but this is a good resource for 040 mask revisions, as well as 'fakes', which can prove problematic with eBay listings.

L88M, the final mask revision, is by all accounts the best-running version of the CPU and most thermally stable. Many other communities, we Mac enthusiasts and Amiga owners, started to snatch them up. Most of the fakes out there will be this mask revision. I wish there was a comprehensive guide to spotting them, but I'd search the forum for '68040 fake' for the bits and pieces members have put together.

edit: here's one: https://68kmla.org/bb/index.php?threads/counterfeit-68040-l88m-mask-revision-from-ebay.36759/

Sorry this is so long-winded but TL;DR, fakes abound on eBay, and you want to be careful.

I bought a genuine 040 from Herb Johnson (if you're stateside he'll ship to you, don't know about international). Also the site can be ...frustrating to get around, but persevere I also bought another one from a stateside eBayer, but apparently it was a mixed bag. Mine was genuine, others' were not... these were E42K mask versions--better than older XC, but they still need a heatsink. I just ordered up a couple of L88M versions from a highly reputable seller (in itself a feat in this space) on the other side of the Pacific from me. I'm hopeful with these. the common phrase with these is they run 'cool to the touch,' which I assume means without the need of a heatsink...We'll see.

That being said, you can overclock most 040 silicon. Bumping a 33Mhz chip to 40MHz with a proper heatsink (and probably fan would be advised) it can be done.

jessenator said:

Any 68040 (that isn't a late model "V"at-the-end (which is 3.3V)) PGA package will socket into am 040 Mac

Click to expand...

I wanted to reiterate this point.

Anything that looks like "MC68040nnXXV" is not compatible. It's a 3.3V embedded application version, and ours need 5V.

Wow! Thanks Jessenator. Awesome info. I've emailed Herb to ask if he has one available.

Let us know if Herb has any. I'd be in the market for one too. Thanks!

For anyone in Europe, there is a source in Germany too:

https://www.vesalia.de/d_68040.htm

They sell it as "tested up to 40 Mhz" although it says 25 on the chip. - I got a XC Revision E31F and it works well in a Performa 630. Without a heatsink it gets warm but not hot enough to burn your fingers. It probably helps that the 630's fan sits directly on top of the CPU.

I'd rather not overclock it without a heatsink though!

mattsoft: I just ordered one from Herb. Shipped to me inside the US, it cost total $78, which compared to eBay was expensive, but considering that you know with much more certainty that the chip isn't a fake or re-labeled, is worth it.

FYI: the 68040 @ 40Mhz installed super easily into the Performa 630CD cpu socket. I didn't even need one of those fancy CPU pullers. I just used a small flathead screwdriver and gently and slowly plied and pried my way around the edge of the CPU. About the second time around, the CPU popped right out. The "new" one slid right in without any issue and the Performa fired up, no problem. Of course, I haven't moved the resistors on the bottom of the logic board yet, so the 40Mhz CPU is only running at 33Mhz, but its running just fine. No software changes required at all.