Macintosh II supporting more than 8MB of RAM issues

[jasa1063]

I just acquired a Macintosh II. Installing 8x4M 30-pin SIMMs, I get a black screen and a sad mac tone. 8x1MB 30-pin SIMMs work just fine. It does have the FDHD upgrade but, still has the Apple AMMU installed. The ROM version is $0178 according to the info screen in SpeedOMeter. So is this a ROM issue or does it require a MC68851 PMMU to work with more than 8MB of RAM or could it be something else I am missing? I already posted a request for a MC68851 PMMU. Any help would be appreciated.

 

[jasa1063]

I found out you need PAL SIMMs if you want to use more than 8MB of ram on the Macintosh II. There are some on Garrett's Workshop on Tindie, but are currently out of stock.

 

[Kai Robinson]

Myself and Phil Cranmer made some open source ones you can make yourself - no need for PALs either as the logic is discrete instead:

https://tinkerdifferent.com/threads/4mb-macintosh-ii-iix-30-pin-simms.27/

 

[jasa1063]

Myself and Phil Cranmer made some open source ones you can make yourself - no need for PALs either as the logic is discrete instead:

https://tinkerdifferent.com/threads/4mb-macintosh-ii-iix-30-pin-simms.27/

Awesome and thanks!