Anyone ever upclock a Sonnet Presto?

[olePigeon]

I have a 25 MHz 68040 Sonnet Presto NuBUS upgrade. I was recently at my local surplus and bought an 80 MHz crystal and an 040 socket. Should I happen across a 40 MHz 68040, can I just swap the CPU and crystal? Or is it not as easy as that? Usually isn't.

 

[Unknown_K]

Will all the onboard chips run ok at 40mhz? How will the crystal speed change affect the CPU to PDS slot speed? Also you would need a pretty big heatsink on that chip (is there clearence?).

 

[trag]

On the Daystar upgrades, my experience has been that the 25MHz models up-clock to 40 MHz without problems. I didn't even need to swap out the 68040 for a faster model. I think I usually added a heat sink to the 68040. I don't know if the Sonnet has similar head room though. Daystar products were the best in their day.

That doesn't look so much like a NuBus upgrade as an LC slot upgrade to me, although it's hard to tell from the photo. I'd do a little more research before plugging it in and powering it up.

 

[olePigeon]

Sorry, it is LC PDS slot. I'll go buy a 60 MHz crystal and baby step it.

Actually, there might be clearance for a heatsink now. I recapped my LC motherboard with type B tantalum capacitors, so there's tons of room now. I guess the only thing to do is try it. Gonna head to the shop for a 60 MHz crystal.

 

[olePigeon]

I put in a 60 MHz crystal and the machine froze the moment it got to loading the Sonnet extension. So there must be something more to it. I'm not savvy enough to test it, so I'll just put it back to stock. It was worth a try.

 

[theos911]

Maybe it is something with the bus timing ratios being off and the extension expecting slower data access. You know, how if you overclock a Powerbook in this manner, the modem will die on you, or the PCMCIA cards or other random logicboard things. /justathought

 

[olePigeon]

You're probably right. Was worth a shot.

 

[theos911]

Maybe you could go back to the original crystal and turn off some options in the extension. Can you use it to turn off the cache? or possibly other things?

 

[olePigeon]

I already resoldered a new 50 MHz crystal on. Don't wanna press my luck, I'm not a terribly good solderer.

 

[Bunsen]

What machine are you using this in?

I already resoldered a new 50 MHz crystal on. Don't wanna press my luck, I'm not a terribly good solderer.

Suggestion: if you do any more attempts, replace the crystal with a socket, so you can plug & play with new timings.

 

[theos911]

I make my suggestions, because I recall recall reading on HHHH or whatever it was about his DOS card cpu transplants. Some of the new cpus wouldn't post. Others worked if he disabled the L2 cache, while others disabled it for him.

 

[olePigeon]

It's a Mac LC with a full 25 MHz 68040 Sonnet Presto in the LC PDS slot.