520STM C070243 REV.C ram upgrade question

[chamlis]

So I have an older 520STM (has modulator but no internal floppy drive) and bought the ram upgrade kit. Do I really need to remove all the ram chips on the board? I read somewhere that all you need to do is snip a resistor somewhere, and/or bodge some wires? Needless to say, I would much rather do that than messing with all of the chips.

Can anyone shed some light on that?
Here's what the board looks like:

c070243revc.jpg

Thank you thank you thank you

[exxos]

Everyone will tell you to disable the old ram, but that's not a good idea. Your just stressing the MMU, PSU and often people swap ram due to faults which risks killing the new ram aswell. Some users reported stability issues as well.

Its all in the FAQ on the install page.

https://www.exxosforum.co.uk/atari/last ... /index.htm

Don't take shortcuts and do things properly right at the start. Save yourself a lot of future trouble.

Theres videos on my channel on how to safely remove the old ram.

[rubber_jonnie]

I have one of these machines and TBH I couldn't make it work with the old RAM installed. I have a 4MB expansion in mine.

Now to be fair, it may well have been due to the remains of the old piggybacked RAM expansion, but you'd be better off removing the RAM to make things clean and simple, not to mention what @exxos said.

Also, when it comes to fitting the MMU adapter, and to a lesser extent the Shifter adapter, I would suggest that you do NOT do this with the mainboard inside the case.

It's better to have the board out and on a completely flat surface with a piece of cardboard (Or similar) underneath to prevent board flex when installing. This is really important to avoid flexing the board as this can pop vias where you can't see the damage and then it's a LOT of work tracing what's wrong.

I learned that the hard way, so it's worth taking the time to give yourself the best chance of success.

[chamlis]

Fair enough. Thanks guys. I'll see about getting a soldering station on amazon.

[rubber_jonnie]

Fair enough. Thanks guys. I'll see about getting a soldering station on amazon.

If you haven't soldered before, and you post suggests you haven't. I'd suggest you practice before doing anything. The ST boards can be quite fragile and desoldering can cause a lot of damage if you're not familiar with the process.

Also don't be tempted to just go for hot air either as it's very easy to 'popcorn' ST PCBs. This is where air trapped in the layers of the PCB heats up and expands causing the layers to pop apart, potentially causing unrepairable damage.

The safest way, IMHO and others may disagree, is to snip all the chip legs at the top by the chip body and then remove each leg one at a time once the chip body is out of the way. Just heat the leg and pad until the solder becomes liquid and pull the leg out with tweezers.

This is very time consuming, however it is the best way to avoid board damage as the legs will come out quickly without putting too much heat into the board, and even if you wanted to reinstall RAM IC's later, 41256 ICs are pretty cheap.

[stephen_usher]

I'd also suggest getting a soldering training kit such as this: https://www.amazon.co.uk/Gikfun-Solderi ... 0F1JPKYPQ/

You can then make mistakes without it being a disaster.

Probably a good idea to get some 60/40 lead-tin solder, 1.2mm diameter, 100g will be enough: https://www.ebay.co.uk/itm/326879942204

[exxos]

Fair enough. Thanks guys. I'll see about getting a soldering station on amazon.

I suggest you watch my video on how to remove the old RAM. Using side cutters you can cut the old IC away for starters to get up and running. Then heat up and gently pull each pin out one by one with some flux. Its pretty simple to do.

Most people try and remove the whole IC in one go and end up destroying the thing.

[chamlis]

I've soldered one thing before, and that was a pi pico onto the SideCart PCB.
Desoldering complete. The chips are even intact, though some of the legs are a little bent. There were a handful of solder points that wouldn't come up with the gun, so used a regular soldering iron and a tweezers to pry them out gently.

I'm not certain if the orientation of the RAM board is correct though. It matches other similar boards I've seen.

IMG_20260314_153544267_HDR - Copy.jpg

[exxos]

STEP 2 - FITTING MMU RAM PCB on the install page shows how to locate the board.

[rubber_jonnie]

Looking at the instructions, and you need to look at the 'Addendum - 2021+' part of section 2, I believe your MMU board is incorrectly oriented, probably 90 degrees rotated from where it should be.

Your board has a white oval on top to indicate pin 1:

Screenshot 2026-03-15 at 10.09.34.png

This needs to align with pin 1 of the MMU as per the image.

Pin 1 is indicated on the mainboard with a white '1' as shown and also the MMU has a chamfered edge with a dot in it that indicates pin 1 of the IC.

I believe pin 1 is along the front edge of the MMU in your case so the adapter needs to be rotated 90 degrees anti-clockwise so the white oval is at the front.

If you look at your board you can see the numbers 10 & 26 along the left hand side of your MMU socket, so whilst I can't quite see the '1' the other numbering indicates that pin 1 is along the bottom edge, since the pins are numbered anti-clockwise starting at pin 1.

Please re-check and follow the instructions in the install guide or you could end up damaging something. Note that MMU orientation is very much dependent on the mainboard revision and I've encountered it in at least 3 different positions.