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Mac SE - Accelerating an accelerator

ObeyDaleks

Well-known member
Hi. I've been experimenting with my Mac SE accelerators, and apparently you can upgrade at least some of them. I haven't tried any others, but I was able to bump the speed on my Novy ImagePro by replacing the processor, FPU, and the crystal oscillator (from 25Mhz to 33Mhz). This was easy/cheap since I already had a spare CPU/FPU combo, so I only had to source the oscillator. The Novy card allows you to simply pull out the oscillator and replace with another.

Now I want to try and upgrade to 50Mhz. I'm assuming this will work because the ImagePro actually had a 50Mhz variant. What I'm confused about is the FPU. The card has a PLCC FPU socket, but I believe 50Mhz 68882 only comes as PGA?? If that's true, what are my options? Would it be safe to overclock a 40Mhz FPU?

Another option I considered - there is another oscillator socket that's unpopulated. I believe this may be for a separate FPU clock, in case you want to run it at a different speed. So it might be possible to run the CPU at 50Mhz and FPU at 40Mhz. Is that feasible?

Any info would be appreciated. I guess I can experiment but I'd like to avoid breaking samething or ending up buying a bunch of stuff that's not going to work. Thanks.

I do plan to try and upgrade my MicroMac card as well, the same way. That one has a soldered oscillator so it's a bit more work. But I'm hopeful it will work.
 
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Phipli

Well-known member
An overclock to 50MHz might be pushing it as sometimes on lower speed grade cards they used slower / cheaper programmable logic chips, this seems to be the case with my Total Systems board. Do you have a photo of the board?

It's likely the second clock is for the FPU, their should be a jumper for selecting which clock it uses?

Running the FPU and CPU at different speeds is perfectly OK.
 

ObeyDaleks

Well-known member
So I decided to try it with a slower crystal in the second socket and it looks to be working. I couldn’t find any software that actually reports the FPU clock speed but I just benchmarked it and it came with slightly lower results using a slower oscillator in the spare slot. I ordered a 50Mhz 030 and a 40MHz 68882 (two of them in case I fry one), as well as 50Mhz and 40MHz oscillators. My plan is to try with 50, and if the board doesn’t like it, I’ll just run it at 40.

54DE7A16-296C-456C-AFCE-65189DE2B8FC.jpeg

In case you’re wondering, the memory jumper got torn off because it was sticking out too much and catching on the chassis every time I tried to pull it out so I had to hard-jumper it to 16MB and then do some trace repair (skills courtesy of Branchus Creations). It’s not pretty but works well.
 

chiptripper

Well-known member
Not a lot of clearance for these accelerator boards is there? I had to slightly bend the chassis just to remove mine without damaging the onboard RAM.

Now I'm thinking I'll have to get it to 40 or 50 MHz too. :)
 

ObeyDaleks

Well-known member
An overclock to 50MHz might be pushing it as sometimes on lower speed grade cards they used slower / cheaper programmable logic chips, this seems to be the case with my Total Systems board.

By the way, I checked the data sheet for the PLC (EP1830-25CFN) and it’s supposed to be good for speeds of “up to 50Mhz”. So it’s looking good.
 

ObeyDaleks

Well-known member
Not a lot of clearance for these accelerator boards is there? I had to slightly bend the chassis just to remove mine without damaging the onboard RAM.

Now I'm thinking I'll have to get it to 40 or 50 MHz too. :)

Yeah, I have another one that’s much worse. The CPU literally catches on the little lip on the bottom of the SE chassis. Bending didn’t help, so I have a method of twisting it diagonally to line up the teeth on the side of the board LOL.
 

ObeyDaleks

Well-known member
Thanks. I tried Norton Utilities and Apple Personal Diagnostics and neither of them gave me the FPU speed. They both list the CPU speed and the FPU type (but not speed). I might try TattleTech.
 

ObeyDaleks

Well-known member
So I tried two different brands of crystal oscillators, and the card wouldn’t run at 40 or 50Mhz. I get a chime and then a sad mac screen. So @Phipli you may have been right about some other components on the card not wanting to run at higher clock speeds. Of course, I could have done something wrong. Perhaps I got the wrong oscillators, although I tried to match the spec as well as I could. This specific card did have a 50Mhz variant, but it could have been a later revision with beefier ICs. Not sure.

On the bright side, I was able to upgrade my other SE accelerator, the MicroMac Multi-speed, from 16Mhz to 33Mhz using the same technique (simply swapping the CPU, FPU, and crystal). So now I have two SEs, both running at 33Mhz with 16MB ram. They benchmark about 2.1x -2.2x the speed of a stock SE/30, the MicroMac card being the faster of the two. I’m reasonably happy with that, although I might tinker some more in the future.
 
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Phipli

Well-known member
So I tried two different brands of crystal oscillators, and the card wouldn’t run at 40 or 50Mhz. I get a chime and then a sad mac screen. So @Phipli you may have been right about some other components on the card not wanting to run at higher clock speeds. Of course, I could have done something wrong. Perhaps I got the wrong oscillators, although I tried to match the spec as well as I could. This specific card did have a 50Mhz variant, but it could have been a later revision with beefier ICs. Not sure.

On the bright side, I was able to upgrade my other SE accelerator, the MicroMac Multi-speed, from 16Mhz to 33Mhz using the same technique (simply swapping the CPU, FPU, and crystal). So now I have two SEs, both running at 33Mhz with 16MB ram. Both of them benchmark about 2.1x -2.2x the speed of a stock SE/30, the MicroMac card being the faster of the two. I’m reasonably happy with that, although I might tinker some more in the future.
33MHz SE with 16MB RAM is a very usable machine. I have a 40MHz clock in the upgrade I've mainly been using. I use the card's divide by 2 switch to run it at 20MHz normally, and 40MHz when challenged by a troublemaking SE/30.

That card will do 40MHz, but crashes at 50. Sounds like a similar scenario to yours.
 

Phipli

Well-known member
Cool stuff, wondering if the sync is a bit off between system and accelerator in the configs that don't work?
I suspect the programmable logic isn't high enough speed grade. You wouldn't spend the extra money on fast chips for 50MHz operation on a 20MHz board.

This is the case with mine, comparing to faster versions of the same card, they have faster grade chips.
 

ObeyDaleks

Well-known member
Thanks guys. This was more of a fun experiment, I mean what else am I supposed to do with my time? Obviously the SEs are pretty blazing fast running at twice the speed of stock SE/30 (and over 9 times their own stock speed). I have a couple SE/30s that are way more pimped out, but I have a soft spot for the original SE since it was my (dad's) first personal computer.
 
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