Overclocking a Performa 630 DOS Compatible

[AndiS]

Hi!

I have a Performa 630 DOS Compatible that I want to "spec to the maximum" - at least as far as possible.

It came with the DOS Card and a Comm-Slot Ethernet card. I increased the RAM to the maximum, replaced the HD with a CF card and was given an AV-card and tuner for it. Now i secured a source for a "full" 68040 Chip with FPU. It's from an  Amiga supplier, so I don't have to sacrifice another Mac for it and the Performa can suddenly transform into a Quadra

The last thing I can think of is increasing the clock speed from 33 to 40 Mhz. I read that this normally does not pose any issues and would just go through with it if it weren't for the DOS Card. Anyone with experience in that regard? Does this mess up timing or clock speeds with the included AMD 486?

I would be happy to hear from anyone who tried this before. And I would also like to hear suggestions about how to "spec up" this machine even more

 

[Brett B.]

I did the full '040 and overclock mod on mine and it has been working perfectly for several years now.  I did add a 468 heatsink and fan to the '040 chip - I think that's a must.  Huge improvement, I have no regrets and the DOS card seems to be unaffected.

Seems like I also upgraded the 486 chip in mine as well, don't quite remember though, that happened close to 20 years ago now.

FYI the published max RAM limit in these is not totally accurate.  I have 148MB in mine.  I thought it was 52MB for the longest time, as is published, but I ran across a 64MB stick that worked...so I bought a 128MB stick, which also worked.  I'm assuming your motherboard has 2x RAM slots so you can get to 148MB by using 1x 128, 1x 16, plus the 4MB onboard.

 

[AndiS]

Yess! - This sounds encouraging as hell - I'm not sure if I include another Fan, besides the Power Supply, but I will definitely add a heatsink. The 486 has one already, the 68LC040 does not.

I've read something about the RAM limits not being that strict already. I found the 32 MB Sticks somewhere (for the DOS Card, and the Mainboard) and stuck with them. If I come across something bigger, I will definitively give it a try. The Single Bank/16 MB limit still applies to the second slot as it seems?

 

[johnklos]

On the Mac motherboard, you can have up to 196 megabytes. One slot will take 128 megs, the other (if you have it) will take 64 megs, and of course there's 4 megs soldered on.

I tested my Quadra / Performa 6xx with the motherboard at 25 MHz with a NewerTech Quadra Overdrive running the CPU at 50 MHz, and with the motherboard and CPU running at 40 MHz. Because all bus access slows down the Quadra Overdrive to 25 MHz, things were mostly faster at 40 MHz.

 

[AndiS]

Wow, 196 MB sounds impressive, If I can find SIMMs that big. There remains the question what software to install that needs that amount of RAM on System 7.5.5

It would probably easier to fill up RAM while using MacOS 8.1 - Only I never could get the DOS card running under that system version so I'm back at 7.5.5. But that's a different story, so thanks for all your input!

 

[nickpunt]

@johnklos interesting, was always curious about how that performed. Have you tried running the bus at 33mhz making the Quadra Overdrive run at 66mhz? Perhaps one of the later stepping models like L88M could handle such a frequency. 

Alternately wonder if there's a way to create a 1.5x multiplier. As you pointed out last year in another thread, the next forums have schematics for the doubler. Such a cool project!

Other question is for 630/640 DOS Compatible if anyone has ever gotten another CPU running in it (like a dx4), aside from the shipped dx2/66 or cyrix 70?

 

[Byrd]

Other question is for 630/640 DOS Compatible if anyone has ever gotten another CPU running in it (like a dx4), aside from the shipped dx2/66 or cyrix 70?

I can confirm a both the DX2 and DX4 Overdrives work fine (5V regulators on chip), and fancier upgrades like a Kingston Evergreen 5x86 133 POST and boot to vanilla DOS but are highly incompatible with more modern memory managers, Windows 3.1 and 95. 

There is the same effect on the Quadra 610, 6100 DOS compatible card - they are very similar.

 

[Brett B.]

I have not been able to get anything larger than 32MB to work at all on my DOS card.  I've experimented pretty thoroughly with that... any module smaller than 32MB works fine, nothing larger works at all or is only recognized as 32MB.  Seems like a pretty hard limit but I don't have any single sided modules larger than 32MB - in any case, 32MB for the DOS side is way more than enough.

I have also not been able to get anything larger than 16MB to work in the second slot in the motherboard but if I remember right it was an issue of using single sided SIMMs in that slot........ IIRC my 32, 64 and 128MB SIMMs are all double sided.  196MB is a ridiculous amount of RAM for one of these, even 148MB is for that matter.  I'll never use it all.  I did it simply to see if I could.  The memory was not super expensive - I think I had under $50 into the experiment. 

As with most things associated with this hobby, the costs are kinda weird.  Putting that much memory in my LC630 when I was actually using it in around 2000/01 would have never been possible on a teenager's budget.  Now, for the cost of an average night out at the bar/movies/dinner/etc I can drop a stupid amount of memory in it - something that probably would have cost hundreds of dollars back in the day.  The computers themselves seem to have increased in value significantly but certain upgrades are dirt cheap now.

 

[AndiS]

@Brett B. - Very true. With a bit of patience and luck you can build your past days dream machine for almost nothing - as long as you are not behind things like an original 128k or a Lisa, or a 20th Anniversary Mac etc.

I've had this 630 for almost 20 years, when it was thrown out of a university. Everything was either very cheap or I even got it for free Luckily the 630 shares a lot of parts with the unloved 6200/6300 PowerMacs - Easy and cheap source for upgrades. That's how I got the AV card/tuner for free even

Since the Pandemic there have not been many nights out at the Bar, so I'm well prepared to sink 40 Euros into the CPU Upgrade ;-) for one of the nicest 68k Macs in my book.

 

[johnklos]

Alternately wonder if there's a way to create a 1.5x multiplier. As you pointed out last year in another thread, the next forums have schematics for the doubler. Such a cool project!

I have an L88M CPU, and I tried it at higher speeds, and got nothing. I suspect the clock generator chips can't run that fast.

On the other hand, if we recreated all the clocks that come from the clock generator ourselves, we could test lots of things... Hmmm...