exxos's Atari, Amiga & retro forum

Hi I am wanting to.upgrade a 520'ST to 4 MB. What is involved and what is the easiest way to do this. It has 512 :-/ in it right now , it's kinda useless right now so it sits on the shelf waiting for better days. Oh and I will be paying someone to do this for me. Russ

Nothing is really easy, but this kit is probably the simplest solution..

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

Okay at some point I will purchase the fully assembled kit, I have the $$$ in savings. Russ

Just be aware Russ, part of this comes as a kit, specifically the shifter adapter, and it will require some resistors lifting and pinning to 5v.

If your soldering skills are still not up to par, I'd strongly suggest that you find a friend who can do the assembly and de-soldering parts for you.

rubber_jonnie, for a 520st can you tell me where those resistors would be? Trying to do this right now with Exxos kit.

James

Bikerbob wrote: 08 Oct 2019 13:44 rubber_jonnie, for a 520st can you tell me where those resistors would be? Trying to do this right now with Exxos kit.

James

Which board is it James? C070709 etc etc..

The only ST diagram has this..

So R133, R134..

Though I believe it was RJ who found those resistors don't exist on some ST's.

But even so, this is only for a test, the old ram needs to be removed for long-term use.

Just to clairify for all, what happened was I missed this part in the Last upgrade instructions.. It looked plug and play.. I plugged it did not play. What happened when started is I got 512k in bank 0 and 2048 in bank 1 - RE-reading showed me.. I did not disable the ram. Since this machine only had bank 0 of ram.. I assume thats why mem showed the 512k I did not disable and then the 2048 in the next bank. The machine ran fine, I ran mem tests all good.. So fingers crossed I did not do anything damaging.

So following this schematic and Joska's PDF. It would seem right that this would work. Joska pulls it from the memory side of the resistor and solders to the pad.. pulling the leg on the MMU side and tieing those 2 together is easier, and I see in the other installs where there are 3 or 6 resitors thats the way its being done, so I assume I can do that.

I hear you Exxos about the the mem chips, but I am not desoldering these chips. I will cross any power issues when I come to it. As this machine is using an external power Supply - more power if it ever becomes and issue can be addressed.

You lift the end of the resistors you circles in black, then connect the now free end of the resistors to 5V.

Removing old chips isn't just down to power, its stability. Or should one of the old ram chips fail which they often do, you could end up shorting out & blowing the 4MB board along with it. if you do not want to desolder them, just cut the pins with some cutters and remove them that way.

Didnt work... in fact worse off.. now I have BSOD