Page 1 of 1

520 STFM 256kx4 DIL to 1Mx4 SOJ

Posted: Sun Apr 15, 2018 12:21 pm
by troed
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
memory1.JPG (216.21 KiB) Viewed 1819 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
memory2.JPG (151.24 KiB) Viewed 1819 times
memory3.JPG
memory3.JPG (272.18 KiB) Viewed 1819 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
memory4.JPG (273.4 KiB) Viewed 1819 times

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

memory5.JPG
memory5.JPG (521.6 KiB) Viewed 1819 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 ...

Re: 520 STFM 256kx4 DIL to 1Mx4 SOJ

Posted: Sun Apr 15, 2018 9:47 pm
by exxos
Today's geek points go to Troed :thumbup:

Re: 520 STFM 256kx4 DIL to 1Mx4 SOJ

Posted: Tue Jul 03, 2018 4:48 pm
by 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.

Re: 520 STFM 256kx4 DIL to 1Mx4 SOJ

Posted: Tue Jul 03, 2018 6:53 pm
by troed
Forgottenmyname wrote:
Tue Jul 03, 2018 4:48 pm
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.

Re: 520 STFM 256kx4 DIL to 1Mx4 SOJ

Posted: Tue Jul 03, 2018 6:57 pm
by PhilC
Thanks, thought it might be but still a RAM Newb here :-)

Re: 520 STFM 256kx4 DIL to 1Mx4 SOJ

Posted: Sat Jul 14, 2018 8:21 pm
by 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.

Re: 520 STFM 256kx4 DIL to 1Mx4 SOJ

Posted: Sat Jul 14, 2018 8:54 pm
by troed
Forgottenmyname wrote:
Sat Jul 14, 2018 8:21 pm
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 :)