520 STFM 256kx4 DIL to 1Mx4 SOJ

Upgrade your RAM from ST to Falcon.
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520 STFM 256kx4 DIL to 1Mx4 SOJ

Post by troed » Sun Apr 15, 2018 12:21 pm

I recently acquired a 520 STFM (IMP chipset, 4 DIL RAM chips, see viewtopic.php?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.
memory1.JPG (216.21 KiB) Viewed 374 times

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

memory2.JPG (151.24 KiB) Viewed 374 times
memory3.JPG (272.18 KiB) Viewed 374 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.

memory4.JPG (273.4 KiB) Viewed 374 times

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

memory5.JPG (521.6 KiB) Viewed 374 times

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 ...

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Re: 520 STFM 256kx4 DIL to 1Mx4 SOJ

Post by exxos » Sun Apr 15, 2018 9:47 pm

Today's geek points go to Troed :thumbup:
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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