How to upgrade OLD 520STm from 512K - hard to find info

[wood_jl]

Greetings everyone.

I am very new to this forum. I am just now getting reacquainted with the ST after about 20 years.

My favorite model is the original 520ST. Specifically, the 520STm. I really really like this machine. I want to use it as my "main" ST. I am in U.S. so this is a Yankee model.

I bought launch model back in 1985. EVERYBODY was doing the "piggyback" 1MB RAM upgrade, even local Atari dealer in Anchorage, AK did this nonstop every business day. While as much memory as is easily possible would be nice, 1MB is enough, and it was my assumption this would be easiest. Atari did not sell "520ST+" here but it is my understanding this was a factory machine with the piggyback.

I have searched (Google, as well as this forum) trying to find a text file, or better yet a PDF of good instructions on this mod and I have no luck. I did manage to find this thread on atari-forum, from 2004:

http://www.atari-forum.com/viewtopic.ph ... 04&p=31664

Unfortunately, the thread is not complete and was locked. There was a user called "DoomMaster" who was attempting to do this very mod and it looks like they were not in good standing here and I am guessing that has something to do with the thread being locked????

I contacted Best Electronics (California) and asked about this mod. I thought perhaps they would sell a kit with the 41256 DRAMs (is this correct?) and some instructions, or perhaps perform the upgrade for a fee. I received back the following reply"

A. Our Atari 25+ year Super Tech does not recommend this 520ST Ram Upgrade. When they do go bad (and they do) they are about impossible to repair. Our Super tech will not even touch one that comes in for repair.

Discouraging. So it is not looking good. I did ask about other possible upgrades but did not get a specific answer; I am led to believe what I desire - 1MB 520STm is a black sheep that I may not have?

Can somebody point to a diagram of this mod, or suggest an alternative? The 72-pin SIMM mod that I saw looks very complicated for me. Are there other users who may have suggestions? As popular as this mod once was, I am stunned at its obscurity today.

Are the RAM upgrades for the STfm series different and incompatible with the old 520ST? If there is one that works, can somebody smarter than me please tell me about it - what it is called and where it is available? I hate to think I have to give up on this, as my heart was set on the original ST. Thank you very much!!!!

[wongck]

Not sure about your 520STM but my 520STFM was simple to upgrade to 1MB, just solder in the missing ram plus the capacitor at the area where there's missing the ram.

[wood_jl]

Not sure about your 520STM but my 520STFM was simple to upgrade to 1MB, just solder in the missing ram plus the capacitor at the area where there's missing the ram.

Hi, thanks for the reply. I have 520STfm as well, and I will be interested in doing exactly this. Would you perhaps be able to point me to a guide for this procedure? (i.e. I don't know about the capacitor, and anything else I might need to know)

Was really hoping to find a guide for the original 520ST though as I have much reverence for this classic. Anybody?

Thanks.

[simbo]

if you look in the guides section youll see a pictorial guide im making up

i have a stm its a 512k machine has no floppy
so is a slim st or an st small

im going to

1}replace the mmu with a later one
2} add some i/o resistors to the mmu and some wires
and add a 4mb 72pin simm
3} wire up all the rest after cutting out the old ram
4} have 4mb and 1mb
5} use tos 1 and 1.04 as this one has v1 tos non floppy so has the 6 soldered roms

this is the next task i was waiting for ribbon cable and some bits and 72pin sockets

youll find the ongoing guide here
http://www.atari-forum.com/viewtopic.php?f=74&t=18614

[wongck]

Hi, thanks for the reply. I have 520STfm as well, and I will be interested in doing exactly this. Would you perhaps be able to point me to a guide for this procedure? (i.e. I don't know about the capacitor, and anything else I might need to know)

I did it but that was back in 1988/89.... so really cannot remember the details.
I think there was already markings on the mobo that specify the ram area and capacitor (or resistor... not sure).
Just look at your mobo and if there are already markings for the ram, you home & dry.

[ralcool]

I upgraded a 520 STFM once using the 16pin x 16 chips in the vacant holes. (Using -120ns ram from an old video card)

262 solder joints later (+ 3 resisters for CAS/RAS) I had a working 1040ST!

Basically easy.

[spiny]

I didn't do the upgrade myself, but here are pics of a bare 512 stfm and an upgraded one, hope it helps

bare 512:


upgraded to 1024:

[wongck]

I didn't do the upgrade myself, but here are pics of a bare 512 stfm and an upgraded one, hope it helps

bare 512:
upgraded to 1024:

Yes, that's it, the same.
It all marked out, ready for the DRAMS.
Just follow what ever DRAM specs and capacitor specs, it's was that easy.

Didn't count the number of solders but at the end of the day my 520STFM became 1040STFM

[DarthWhippet]

I have a spare 520STFM motherboard i would like to upgrade to 1040 but the RAM is surface mounted on the bottom left, and they don't look like they can be socketed It's a C103088 Board. Would it be worth doing and more importantly any idea where to get the RAM?

[wongck]

Get a memory upgrade and go to 4MB.

[DarthWhippet]

Get a memory upgrade and go to 4MB.

Can you point me in a specific direction?

[techie_alison]

http://www.logicsays.com/atari/72simm/

That'll give you a rough idea. As long as you're methodical and do your homework, then you'll spot the wiring mistake in it.

It's pretty much the same across all of the issues, but you need to read up to UNDERSTAND what you're doing, and why.

[wood_jl]

Anybody remember the old 520ST, though?

The 72-pin simm upgrade looks to NOT be for the inexperienced/faint-hearted (which is me).


It seems that a doc file for the old "piggyback" 1MB mod just isn't in existence!

I suppose that in Europe, this mod wasn't popular because it came that way already with the 520ST+ ?????????????

For Yankees, this upgrade was done ***constantly*** in the 1986-1988 years. I mean the Atari dealer (Anchorage, AK) used to have them queued up all the time! It's too bad somebody didn't scan the paperwork on this.

I can only conclude:

1) The mod has been lost to antiquity when the Atari dealers all shut down
2) The subsequent popularity of the STf/STfm/STe machines has relegated the original ST/STm to obscurity
3) All the 520ST/m still functioning have either all been upgraded, or were 520ST+ from the beginning; hence no interest
4) The 520ST/m is a scorned machine and very unpopular
5) all of the above

Thanks to all for suggestions, however!

[wongck]

Get a memory upgrade and go to 4MB.

Can you point me in a specific direction?

In addition to techie_alison good instructions, there are other's here.
Not sure if those work as well as techie_alison's.

[techie_alison]

The original ST (the one with the power brick) can be easily taken up to 2MB, with a pair of 30-pin SIMMs. Going up to 4MB though, ...that's a bit more involved as you have to start pulling out lines straight from the MMU. I can't remember quite why I didn't take it to 4MB.

http://www.logicsays.com/atari/520stf/

[ozy2000]

Hmmm the ST and STM are the nicest looking machines of all the standard 'all in one' computer designs of the 80s if you ask me. It's a shame that the piggyback method is nowhere to be seen, I remember reading in one Atari magazine how to do this. It may have been Atari User or ST Amiga Format (combined magazine not ST Format/Amiga Format after it split...I never bought ST Format see)

Here in the UK we didn't really get the 520ST+ we only had the original ST bundle (1 drive and mono or colour monitor) and then straight after this the 520STM was launched and sold alone for I think 399 inc sales tax, think I paid 475 for a very early one with an SF354 drive. Everyone was offering the 1mb piggyback upgrade though for ST and STM users, and for a hefty fee you could take it up to 2.5mb I believe so it was common enough for technicians at the time. But unless someone has that issue of the magazine I read showing you exactly how to do it then it limits the use of the best looking 520/1040 series and that specific mod is gone for good now given the lack of completed ST magazine sets scanned at the moment.

Oh and having mouse ports underneath on the STE/STF....what a silly idea! No such sillyness on my STM

[simonsunnyboy]

In the German magazine c't dated from January 1986 there is an article explaining how to piggyback RAM inside an original 520ST. It has the attached wiring diagram and mentiones 41256C-15 RAM chips by NEC. Finding modern or compatible replacements will be up to the reader.

atari-520st-ram-piggyback.png

Note that the article says you can only mount the piggyback chips if the RAM chips inside are not yet socketed. If the RAMs are socketed, space inside the case will not be enough.

[ozy2000]

I've actually found an issue of the magazine which gives a lovely extensive explanation of doing this upgrade to a TOS on disk 520ST, so therefore same for all ST and STM machines (ie no empty sockets to put extra chips in and none of the RAM is socketed either).

I'll upload the two pages later on (they're on a completely different machine I use for work stuff that never goes on the net usually).

[ralcool]

double post.

[ralcool]

The 'piggy back' ram mod is actually quite straight forward.

Refering to the diagram sunnyboy posted.

The ram chips all see the same data and address lines. Except 3 other signals

Ras 1, and Cas 1 lo & hi.

You can plainly see that Pin 18 of the MMU goes to all the new piggy backed chips..(pin4 for 41256 chips). This is RAS1.
MMU pin 21 is CAS 1 Lo, and 22 Hi. Go to pins 15 of the new chips.

Cas1 Lo goes to half of the new chips, and then Cas Hi goes to the other half.

If you have 16 chip banks, then the half is 8 chips. Sometimes the ST has a 4chip bank. Thus then only 2 each get CAS Lo or Hi.

The trick is whether to wire directly to the mmu (via 68ohm resisters in line) , or if you can find traces or missing resister locations on the motherboard.

As we know, most later ST have heaps of positions on the board to fit another bank of ram chips- you don't have to use them- you can piggy back the first bank, and substitute the new RAS1/CAS1 lines on the new chips.

Older ST don't have any unused positions (only fitted for 512k- often under the keyboard- but the MMU can still provide the RAS/CAS1 signals if we tap into them.

Its easy, and some people find it easier to solder on the back of existing chips, than suck out the unused pads and fit the chips on the MB.
Realise though- many STs have surface mounted ram, and piggy backing is essentially impossible.

When we fit alternative memory upgrades like 72pin simms, or video shifter mounted upgrades- we actually put 5v on these RAS/CAS pins on the 'old' memory to disable them, and redirect the RAS/CAS lines from the MMU to the 'new' ram. Simbo likes to remove the old ram- but this can be difficult and time consuming.

Hope this helps.

[1024MAK]

Below is a pin out of a typical DRAM chip.
Note that you can actually use a number of different makes/types of IC (chip) because many different manufacturers made equivalent types.

For example:
M5M4256P-15 or M5M4256P-12
TMS4256P-15 or TMS4256P-12
HM50256P-15 or HM50256P-12
HYB41256-12
are all equivalent types.
Indeed you often see these types on motherboards and SIMM memory modules

The suffice -12, -15 is the access time (speed) and anything lower than -15 for 150nS (nanoseconds) should work.
The Atari accesses memory at a fixed speed so there is no advantage in faster IC's.
Note that -15 means 150 nS, -12 means 120nS, but -70 means 70nS, -85 means 85nS etc

Just make sure that you get 262144 X 1-BIT DYNAMIC NMOS or CMOS RAM and that it is supplied in 16 pin Plastic DIP or Ceramic DIP types .

M5M4256 pin out (low res).png

[atarisputnik]

Hello, could anybody please post the specification of the capacitors needed for this upgrade? If I understood it correctly, all I need to perform the upgrade are 16 capacitors and 16 41256 DRAM IC's? Thanks for your help!

[1024MAK]

Hello, could anybody please post the specification of the capacitors needed for this upgrade? If I understood it correctly, all I need to perform the upgrade are 16 capacitors and 16 41256 DRAM IC's? Thanks for your help!

The spec on decoupling capacitors is not critical. The normal value is 100nF. The type of capacitor again is not special, but normally ceramic types are used. The physical size and type is also not an issue as long as they fit neatly on the board.
If you are attempting to do a piggy back upgrade (put extra chips on top of exising chips) it's best not to try to fit extra capacitors to the extra DRAM chips.
See http://www.atari-forum.com/viewtopic.ph ... 9&#p170889

You may also need to add some resistors to enable the extra DRAM - see http://www.atari-forum.com/viewtopic.ph ... 9&#p171166

[ktodnem]

Hmmm the ST and STM are the nicest looking machines of all the standard 'all in one' computer designs of the 80s if you ask me

Sorry for bringing this post back up but I just have to say I so agree. I found this post in an effort to figure out whether my 520STm was a rare machine. Definately the most pleasing design.

A friend of a friend who was an engineering student upgraded my ram to 1mb with the piggy back method. I had a look inside then, almost 25 years ago, but didn't takea picture. Has anyone got a picture of a piggy back setup, just for the memory lane?

I might buy a proper ST again, probably from Best Electronic. But I might try to hunt down my old ST, sold in the local paper in 1991. If I find it, willthe ram upgrade cause any trouble, whatwith the reference in this thread to "all" piggy back jobs eventually failing?

Thanks, wonderful forum, been a guest for over a year.
-KT