Upgrading a Memory Upgrade

[Soyale]

I fitted this 1MB upgrade to my 520 STFM back in the mists of time. I remember it being a production since I hadn't soldered anything before or touched the chips in my ST.

I recently revived my dear ST and doing some maintenance noticed that the memory chips on this upgrade are in sockets suggesting that they were once intended to be removable. Maybe the upgrade kits were the same for different sizes except for the actual memory chips.

Does anyone have an opinion or advice on whether I might be able to swap larger memory chips into this board so I don't have to go through the palaver of unsoldering the existing kit etc.

2021-03-08 16.54.18.jpg

[exxos]

If you can find 4bit x 1024k dram in the same package... A9 may not be connected.. You would have to check the MMU pinout for MAD9..See if it goes anywhere on your board...

[Soyale]

I'll have a poke around and see what I can find. The package appears to be DIP-20 and I'm not turning up anything yet. I'll be back for a second opinion if I find something!

https://www.datasheets360.com/part/deta ... 628452897/

[Soyale]

I think this one is close but no cigar right? It advertises as 1Mb but is 4bit x 256kb vs 4-bit by 1024kb.

https://www.ebay.com/itm/MB81C4256-80P- ... 1013142822

Can anyone confirm?

[exxos]

Those are the same chips you have in already 4x256.

[Soyale]

Hysterical, I clearly need to get better at this. If I get the shielding off my ST so you can see both parts, would you be able to advise if one of your kits is compatible amd what would be involved in installation? I'm getting nowhere with the "easy" solution of changing the memory chips.

[exxos]

My kits fit like this...

https://www.exxosforum.co.uk/atari/last/4MBMMU/index.htm

[Soyale]

I took some pictures of the layout of the MMU and shifter on my board, and how they are connected. The memory board just pushes into the MMU. The shifter appears to be plugged into a socket with the cabling that goes to the memory board. That socket is then plugged into the original socket on the motherboard.

It looks like to me that taking out the original update is easy. I'd need to pop the memory board out, take the shifter out of of the socket and take the top socket with the cabling out. From there, I think the installation of your kit would be fairly easy? Am I right? Would I need to build the shifter board or do you have preassembled ones? Anything else I need to think of?

mmu and shifter.jpg

shifter sockets.jpg

shifter box.jpg

memory board.jpg

motherboard revision.jpg

shifter socket cable connection.jpg

[exxos]

My shifter boards have the connector soldered but nothing else as people fit them differently sometimes. It you think its not something you can do, I would send your motherboard to @Steve and have him fit it all for you.

[Soyale]

Which connector is soldered? The ribbon cable to the MMU?