Mac IIsi clock question

[commodorejohn]

So I've been looking at putting a new clock crystal in my IIsi to get the full 25MHz out of it. I notice on Marc Schrier's page that you can get it up to 27.5MHz with the appropriate crystal, but any higher causes problems with the floppy controller. My question is, is there any reason not to take it up to 27MHz?

 

[Paralel]

I guess it would depend on how much leeway there is with regard to the various timings in the system. If the specs are quite tight (5% or less tolerance) then it could easily cause trouble in any number of places, if the specs are lenient (up to a 10% deviation) then it shouldn't be a problem.

The big unknown is how much deviation is already present in the system due to the sheer age of the components. It's basically impossible to know if the two add up together to exceed the tolerance built into the system.

It's probably one of those "you won't know until you try it" situations.

 

[commodorejohn]

Hmm. Maybe I'll try the 27 first and then the 25 if there's any noticeable trouble.

 

[trag]

Hmm. Maybe I'll try the 27 first and then the 25 if there's any noticeable trouble.

I modified a IIsi back when the IIsi was still a reasonably modern machine. It worked great at 27.5 MHz. However, as Paralel pointed out, aging components may play a role.

The biggest problem I had was getting one or two of the original oscillator pins to come loose. The darned thing did not want to desolder. Be careful. as you could probably pull the via out of the board if you're not.