- The LaST Upgrade -


Last updated - February 21, 2024

Visit our Atari webshop HERE


The 4MB "plug in" upgrade is a STFM upgrade kit designed to give 1MB and 4MB switchable RAM expansion.

First let me clarify what "plug in" means. If you purchased the kit fully assembled then there is no soldering needed to build the kit which means it is ready to plug in. Note that I always supply the actual 4MB MMU board assembled and tested. The shifterboard requires some assembly unless purchased otherwise. If you purchased fully assembled then it is generally possible to "Plug in" the kit and that is all that is needed. However, This is only possible if your STFM has a socketed shifter. If it does not, then the shifter will have to be unsoldered and soldered into the adapter PCB. In which case the 4MB kit isn't going to "Plug in". Though that is a problem with your motherboard not the kit. The kit by itself is classed as a plug in upgrade as it is perfectly possible to use it that way ( motherboard supporting of course).

Also it is worth noting that not all STFM's have PLCC socketed MMU's. Some have SMT types in which case it is not possible to fit this upgrade. I do sell another 4MB kit for some STFM revisions so please check out my store for other upgrades. Any upgrades not listed I do not produce. There are so many motherboard revisions it would be impossible to design a kit to fit every single one. So these kits fit the most common revisions. This 4MB kit will fit any ST/STF/M/MEGA machines with socketed MMU.

There are a couple of videos on my YouTube channel with methods how to remove the old RAM HERE. All the old RAM must be removed before starting installation.



The first step is to assemble the shifter adapter. If you purchased this board assembled then you can skip this step. Carefully open the bag of bits which was sent as some parts are small (SMT capacitor) and can easily be lost.

There is a choice to fit the Shifter in a socket or not. Though if you are going down the socketed route, please understand the total height of all the sockets will be to high to fit under the shifter can as shown in the above image. I would recommend removing the motherboard socket and soldering in the adapter pcb directly into the motherboard without the socket. If you keep the adapter pcb with a socket then the shifter may stick up a couple of mm above the shifter can, but that isn't normally a huge problem anyway.

There are a few parts to building the shifter adapter. The PCB, capacitor, IC socket, cable connector and header pins. Most people are going to cringe when they see the fine pitch of the cable connector , but there are easy ways to solder this without having a fine tip soldering iron and a steady hand!

I would first suggest either taping down the connector or using a croc-clip to holder down the connector to hold it in the correct position before you solder it. You need to hold the connector in place and make sure its lined up 100% before you attempt to solder it.

AMENDMENT: Kits supplied in 2018 will have the SMT connector and capacitor on the following board pre-assembled. However, you must check continuity between the cable and the shifter once the shifter board is fully assembled still, as I can only do a visual inspection on the connector after soldering and cannot test it without assembling the whole board.

I use SMT paste for this. Currently I am using "Martin Paste". I have tried others but that is the one I prefer using out of the others so far. Its actually one of the cheapest aswell.

Just run a line a paste over the connections and then run the soldering iron over it.

If you apply to much paste its possible to short out some pins. I would recommend using desoldering braid to suck up the solder.


Once sucked up the shorted pins. Apply a very thin coat of paste to all pins and resolder them. The braid will probably suck up the solder from under the pins so a little bit more solder paste is needed to ensure they are still connected.


Clean up with a bit of IPA solvant and that's the hardest part done :)

The image looks like there is solder under the pins, but it is actually some white printed text under the connector which is making it look "bad". It is useful to have a magnifying glass to double check the joints. They are a pocket "45X Magnifying glass" with 2 small LEDs (takes 3 AAA batteries). I'm not going to link to any sites selling it as there is no guarantee the page will stay up in years to come.

TIPS - You can try normal solder in the pins and suck up with braid and apply a tiny bit of solder to the pins if you do not want to get any SMT paste. It is a lot harder to use normal solder but it is possible to solder pins in a normal soldering manner if you have a fine tip soldering iron and a steady hand. I would advise not to use a solder sucker if soldering goes wrong. The pins are fragile and can become bent while solder sucking. So I really would advise not using a sucker. If you don't want to shop at farnell for stuff, then please only get a good brand braid and paste. A lot of braid sold has not got flux which makes it pretty useless. Also, some cheaper brands state fluxed, but there is so little on it that its almost unusable. Sometimes you can buy 10 meters or more braid "cheap" for the price of 1 meter of quality braid. Though 10 meters of braid isn't going to be good value if it hasn't got enough flux content. As for paste, there is so many brands coming and going every few months its hard to keep track of. I suggest only buying something of a quality brand in a syringe than some cheap pot which probably won't work well.

Next is to solder the IC socket, Capacitor and solder pins. First solder the SMT capacitor on. It does not have a polarity, so it can be soldering in however it lands on the PCB :)

The solder pins have a shorter thicker pin, and a longer thinner pin. The shorter thicker pins solder into the PCB. I strongly suggest the soldering order stated. First cut the header strip in half and place the longer thinner pins into the IC socket. This will help you keep the pins straight while soldering.

Note carefully where the head pins got into the PCB!


I suggest only soldering the row as shown above first. If you rushed ahead and soldered both strips on at the same time, its not a huge problem, but it does making soldering the IC socket harder as the header strip gets in the way.

The pins stick up a fraction higher than the solder. So I suggest trimming the tops off the pins otherwise the IC socket may not seat correctly on the PCB.

Remove the IC socket and take the header strip out of the socket.

Place the IC socket on the PCB and solder it in.

Solder in the second header strip. Make sure the shorter wider pins go into the PCB!


All sorted :) Phew!

What I recommend doing next is plugging in the cable and testing each pin on the cable connects to a pin on the shifter board. Simple use a meter on resistance or continuity test, and place one probe on the cable and run the other probe down each shifter pad on the PCB to make sure it connects somewhere. Do that with each pin on the cable and verify it connects to some pad on the PCB.

I don't have a diagram of the board as such. As its 2 layer and some lines overlap it would be difficult to show what pin connects to what exactly. But as mentioned above, Each pin on the cable will connect to a pad on the PCB. If one does not, then you have a bad solder joint.


The RAM board itself simply pushes over the MMU. Though it is important to know exactly how this fits.

What I did to illustrate the pins location into the socket , was to use longer pins. The board you will be supplied has shorter pins. Though I could not show the pin alignment as the socket is black, the PCB is black, and the bottom of the header pins is , well, black! So those images showed absolutely nothing. The longer pins show clearly how they fit into the socket. Please note the dust is generally not included in the kit :)

I would urge people to make sure the pins are totally straight on the PCB before pushing into the MMU socket.

If you are fitting this to a early ST / STF revision motherboard. The MMU location and orientation could be different. You can see in the above image pin 9 and 10 is printed on the motherboard for the MMU (U56 on that revision) and the cable connector is facing to the right. This means pin 1 of the MMU is the back of the MMU adapter board (back meaning opposite side to cable connector). Also pin 10 and 26 is printed on the adapter PCB & motherboard. So please make sure you have this correct before pushing in the pins. For those who have no idea what I am talking about, here is a image below :)


Later PCB revisions mark pin 1 on the PCB as a white circle. Which matches pin 1 on the MMU / Motherboard as shown above with the red arrows.



The connectors have small tabs each side which pull outwards to allow the cable to be pushed in. Once the cable is in, the tabs are pushed back to lock the cable into place.


The image shows the tabs pulled outwards to allow the cable to be pushed inwards. The cables silver strips are placed upwards into the connector.


Carefully push the tabs back so lock in the cable as shown in the above image.

Next up, if your ST has a socketed shifter, you can push the shifter adapter into the socket and fit the other end of the cable to it. If you do not have a socketed shifter, then you must unsolder it and fit a socket, or solder the Shifter adapter directly into the motherboard (recommended).

So you should look like this once all fitted. Note the cable needs to be folded about if you want it to lay flat.



I generally use the XTRA RAM TEST software. But in 2016 czietz wrote a better RAM testing software YAART018 or YAART021. More information on the forum HERE.

All boards I supply have been tested for several 100 cycles which is the best part of a day. It takes about a hour to do 100 cycles or there abouts. So every kit has a good soak testing before it is sold. Once you have fitted the upgrade, leave it running for a few hours and make sure it functions correctly. If it comes up any errors, then you may have a bad connection somewhere. If you get a black and white screen on power up or vertical black and white bars, then you may have a problem with the cable or connections. So far I have tested 10+ RAM kits and not had any problems relating to fitting. So hopefully thing will be straight foward for people who are fitting it themselves.



Circled in red is the selector for 1MB & 4MB switching. By default 4MB is selected.

If you unsolder the 2 connecting pads, and link the center pad to the bottom pad then this will select 1MB mode. You can of course use a toggle switch to switch between 1MB & 4MB modes. The 3 solder pads solder directly to 3 pins on a toggle switch using wires. So it is pretty simple to fit a switch. I sell toggle switches in my store if anyone needs to order one while ordering the kit.

I would suggest the switch be fitted on the left side of the ST rather than the back of the ST. This is to keep the wire lengths to the switch as short as possible. Unfortunately there is no simple switching method other than isolating A9. So A9 becomes routed via the switch. So keeping the wiring as short as possible is preferable. Routing those wires near the PSU (IE back of ST) could result in noise being introduced into the signal. Ideally I would suggest just leaving the selector jump on 4MB. There are not many games which dislike 4MB as a lot are being fixed in recent years. There is also software alternatives to limit to 1MB though it is not something I have looked into personally.

Enjoy! :)



As shown in the image below. The MMU RAM kit can be fitted to almost any motherboard. Though with the style below, the MMU is located at the front end of the machine which causes problems with the top metal shielding :-(

The good news is, it is fixable, but will take a little work..

Do not attempt to do the mods listed below to the MMU board unless A) you are confident you can do it without breaking it, or B) have deep pockets to buy a new board assuming you break it.


Basically it involves trimming the pins of the MMU adapter and doing some metal editing to the top sheiling.

Shown below is how the MMU board normally fits into place.


The 4 images below show how I recommend cutting the pins. What I do is use a second header strip, pulling all the pins out, then I slot the plastic part onto the MMU PCB pins as a guide to use to cut the pins. Then afterwards, remove the plastic parts, including the one which was on the board originally.

Now, take your time in pushing on the black plastic bits, and removing them and cutting the pins. Cut the pins ONE AT A TIME, otherwise you will balls it up like I did and not get them as "close cut" as you can doing them one at a time :)


The pins now should be all nice and level and about half the size they were before cutting.

NOTE - while you *could* cut them shorter, if you do that, then if any pins get "to short" then they likely won't make contact in the socket, then its game over for you :)

So then you should be looking something like below... There is a 1mm gap between the PCB and MMU. This isn't a bad thing, ventilation ;)


So now the shielding will fit down properly, but the metalwork will touch the corner of the PCB so there is a likelyhood of it shorting out the SMT parts. So we need a dremel next :)

Don't forget to file both sides of the "hole" to remove any "burrs" as they could short the MMU board to the metal!




Images taken by KLund1 on exxosforum

So there you have it, done!

The bottom of the keyboard normally has a plastic sheet stuck on, so worth just checking nothing on the back of the keyboard is going to short out on the board. As you can see from the image, the board does not poke though the shielding, but is right up against it. So it shouldn't cause any location problems with the keyboard :)




https://www.youtube.com/watch?v=giWkXrwaFCQ GadgetUK164's channel on fitting this 4MB kit with various other kits.

http://atari-forum.com/viewtopic.php?f=15&t=29636 Spiny's guide to fitting.

http://www.atari-forum.com/viewtopic.php?f=15&t=30873 Spiny's STM fitting. Main page here http://www.spiny.org/atari/photos/exxos_4meg_stm/