Mac SE - Accelerating an accelerator

[ObeyDaleks]

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.

 

[Phipli]

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]

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.



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]

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]

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.

 

[Phipli]

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.

It was the PALs / GALs and FPGA I had in mind.

 

[ObeyDaleks]

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.

 

[joshc]

I think Norton Utilities, or TattleTech should tell you the FPU clock speed.

 

[ObeyDaleks]

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]

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.

 

[Phipli]

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.

 

[Trash80toHP_Mini]

Cool stuff, wondering if the sync is a bit off between system and accelerator in the configs that don't work?

 

[Phipli]

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]

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.