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Macintosh II supporting more than 8MB of RAM issues
Posted by: jasa1063 on 2024-01-01 11:38:35
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.

Thanks!
Posted by: Phipli on 2024-01-01 11:45:47
The Mac II needs "PAL" RAM if the SIMMs are bigger than 1MB. Normal SIMMs don't work in the II or IIx.
Posted by: jasa1063 on 2024-01-01 11:55:21
The Mac II needs "PAL" RAM if the SIMMs are bigger than 1MB. Normal SIMMs don't work in the II or IIx.
That is the piece of info I was missing.

Thanks!
Posted by: Phipli on 2024-01-01 11:59:08
That is the piece of info I was missing.

Thanks!
Between apple developing the II and 4MB density SIMMs being released, the standards changed and a test mode was added. The behaviour of the II and IIx accidentally triggers this mode and the RAM stops responding, causing boot to fail.

Manufacturers made special SIMMs with additional logic that intercepted the "bad" signals and modified them to prevent the memory chips on the SIMM entering test mode.

You can usually spot them because they have an extra, square PAL chip in the corner of the SIMM, but the exact implementation varies.

For now I'd suggest installing 8MB and use RAM Doubler.
Posted by: robin-fo on 2024-01-01 13:33:16
Could you bypass the issue by upgrading to a IIcx or SE/30 ROM? Or comes this from within the GLUE?
Posted by: Phipli on 2024-01-01 13:33:50
Could you bypass the issue by upgrading to a IIcx or SE/30 ROM? Or comes this from within the GLUE?
It is fundamental to the logic board. You could hack it about by modifying the circuit to match the cx or SE/30... But that would be a bit bodgy.
Posted by: cheesestraws on 2024-01-01 13:47:45
Could you bypass the issue by upgrading to a IIcx or SE/30 ROM? Or comes this from within the GLUE?

As @Phipli says, this is a hardware issue not software. GLUE sounds plausible but I wouldn't want to claim I know. Changing the ROM will achieve nothing.
Posted by: ObeyDaleks on 2024-01-01 15:06:31
Here you go. I’ve used these and they work great.


Edit: Whoops I realized it’s out of stock. Maybe he will make some more soon? You can ask.
Posted by: David Cook on 2024-01-01 17:06:18
Here you go. I’ve used these and they work great.


Edit: Whoops I realized it’s out of stock. Maybe he will make some more soon? You can ask.

Thanks for posting the link. I added my name to the wait list.
Posted by: jasa1063 on 2024-01-18 19:48:16
If you look at the listing on Tindie the last batch was sold Jan 19th 2023. I just wonder if anymore of these are going to be made given the length of time since they were last sold. I got lucky and there was a listing for 2 sets of 4x4MB PAL SIMMs on eBay that are tested with 30 day returns. I grabbed them as these don't seem to come up too often. I just installed a 68851 in my Macintosh II and now I can go beyond 8MB!
Posted by: micheledipaola on 2024-01-28 12:20:14
If you look at the listing on Tindie the last batch was sold Jan 19th 2023. I just wonder if anymore of these are going to be made given the length of time since they were last sold. I got lucky and there was a listing for 2 sets of 4x4MB PAL SIMMs on eBay that are tested with 30 day returns. I grabbed them as these don't seem to come up too often. I just installed a 68851 in my Macintosh II and now I can go beyond 8MB!
I have had the 68851 PMMU ready for months while waiting for these PAL SIMMs, so today I wrote to Garrett on Tindie, to ask if some new batch would be coming anytime soon. Maybe @David Cook if you write too, we can make a bit of a pressure and maybe convince him? I even proposed to make 16MB SIMMs which should be supported by the 68851 PMMU too.
Posted by: pezter22 on 2024-01-28 19:15:55
I bought a couple of these sets for my Mac IIx a year ago. They are great, but I would place some solder onto the pads to give them some extra thickness to connect to the socket. I wasn't able to boot until someone suggested the soldering trick. It's just that the PCB's are thinner than the original SIMMs. I now have 32mb of memory in my Mac IIx.
Posted by: jasa1063 on 2024-02-04 10:27:24
I have had the 68851 PMMU ready for months while waiting for these PAL SIMMs, so today I wrote to Garrett on Tindie, to ask if some new batch would be coming anytime soon. Maybe @David Cook if you write too, we can make a bit of a pressure and maybe convince him? I even proposed to make 16MB SIMMs which should be supported by the 68851 PMMU too.
I was pointed to this open source project on Github for making your own 4MB PAL SIMMs in case you anyone is interested.

github.com

GitHub - kr239/Macintosh-IIx-RAM-SIMM: 30-pin SIMM designed for use in the very finicky Macintosh IIx

30-pin SIMM designed for use in the very finicky Macintosh IIx - kr239/Macintosh-IIx-RAM-SIMM
github.com github.com
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