520 STFM 256kx4 DIL to 1Mx4 SOJ

[troed]

I recently acquired a 520 STFM (IMP chipset, 4 DIL RAM chips, see https://www.exxosforum.co.uk/forum/viewt ... f=56&t=749 ) which I wanted to bring a bit more up to spec. Adding four 256kx4 would've brought it to 1Mb - but replacing the existing four 256kx4 with 1Mx4 would take it to 2MB in total.

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Alright, 20 pin DIP 1Mx4 is really hard to find. Also, I have a drawer full of SIMMs and it's common to find 1Mx4 20 pin SOJ on them. However, SOJ to DIP is a bit complicated. It's possible to carefully stretch the SOJ legs to fit a DIP sockel - but I found a cheap source of SOJ to DIP adapters on Ebay from Ireland: https://www.ebay.com/itm/New-4x-Adapter ... 2749.l2649

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memory3.JPG (272.18 KiB) Viewed 13842 times

Uh oh. The adapters are too wide to just be placed as is (will cover the holes for the chip next to it. I tried sanding one side down as far as possible but still no go.

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Solution: Angle the pins Just not too much - the PSU will sit on top here.

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Final mod. Since these are 1M instead of 256k we now have to manually connect A9 (pin 5) to the unused MMU pin 64. It's not visible in the picture but pin 5 is connected between all the chips on the bottom side of the motherboard.

Unusually enough one of the donor 1Mx4 chips was actually bad (or became bad when transplanted) so I had to hot air the SOJ chips off and on when mounted to find the culprit. I have no idea how I've ever survived without a hot air station before ...

[exxos]

Today's geek points go to Troed

[PhilC]

Great guide, I'm going to attempt something similar to an C103277-___ REV.2.2 Mega ST1.

I don't suppose you know if I can use NEC 4217400-60 4mb x 4 SOJ chips instead of 1mb x 4 as I've got 16 of those and no 514400's or similar at the mo.

Got far too many 8 bit Atari ram chips if anyone needs any.

[troed]

Great guide, I'm going to attempt something similar to an C103277-___ REV.2.2 Mega ST1.

I don't suppose you know if I can use NEC 4217400-60 4mb x 4 SOJ chips instead of 1mb x 4 as I've got 16 of those and no 514400's or similar at the mo.

Got far too many 8 bit Atari ram chips if anyone needs any.

As long as the bit width is correct (the x4) the number of them, if higher, is simply unused. In rare cases the pinout would be different so just check that otherwise you're good to go.

[PhilC]

Thanks, thought it might be but still a RAM Newb here

[PhilC]

Just a quick thank you. I used the method above to upgrade a Mega St1 to 4mb.

There's more space in the Mega for the RAM PCB's but they still have to overlap very slightly.

[troed]

Just a quick thank you. I used the method above to upgrade a Mega St1 to 4mb.

There's more space in the Mega for the RAM PCB's but they still have to overlap very slightly.

Awesome! Glad it was of any help

[gman]

I recently acquired a 520 STFM (IMP chipset, 4 DIL RAM chips, see https://www.exxosforum.co.uk/forum/viewt ... f=56&t=749 ) which I wanted to bring a bit more up to spec. Adding four 256kx4 would've brought it to 1Mb - but replacing the existing four 256kx4 with 1Mx4 would take it to 2MB in total.

Hi, I"m new to Atari ST... I picked up a cheap 520 STFM with the same board (C103175 REV 1), not knowing if it worked.. apart from a missing key and dead floppy drive, it works


Anyway, I was thinking of doing this upgrade, just a few questions:
1: what's the resister on the cable "manually connect A9 (pin 5) to the unused MMU pin 64."?
2: From your pic, did you have to resolder any jumpers ie A16, A17, CE at the bottom (next to HI-0) after the extra ram?

Strangely, my board has the same 4x TC514256P-10's but my 3 jumpers are closed on 1M, not 256k like yours.


3: I see PhilC did this for 4MB, I just want to confirm this can be done on this board also, filling the other bank of 4 using the same method?
4: and if so, where would does the manually connected A9 (pin 5) connect to?

Thanks in advance

[exxos]

1: what's the resistor on the cable "manually connect A9 (pin 5) to the unused MMU pin 64."?

When you upgrade the RAM from say 1MB to 4MB you need a extra address wire, which is what A9 is. Basically without it, your new chips would be "stuck" with 1MB for example.

I see PhilC did this for 4MB, I just want to confirm this can be done on this board also, filling the other bank of 4 using the same method?

It looks like you should be able to copy it yes.

[Maximilian]

As long as the bit width is correct (the x4) the number of them, if higher, is simply unused. In rare cases the pinout would be different so just check that otherwise you're good to go.

While the memory chips of the c64 are getting harder to find the same trick is used, just make sure to tie any unused address lines to ground or VCC, this is sometimes forgotten and can lead to an unstable machine.