First of all we need to remove all the old ram chips. Here I also desoldered the capacitors also, but there is no real need too unless you are really pushed for space.

NOTE - If using a board WITHOUT a SIMM socket, then you likely don't need to remove the capacitor.

The upgrade assumes there was 1MB already in place. If you only have 512K memory, then you will need to fit the 1MB address line resistors which are normally 68R and 33R. This guide does not include fitting of these resistors, but you can see which ones are missing on your motherboard by looking at the row of resistors seen in other images, or look at my 1MB upgrade HERE to see which resistors you need to fit.

TIP - If you are a novice at soldering, I suggest you use a small pair of side cutters and cut the legs off all the chips to remove the chip body. Then heat up the pins left in the board and pull up gently one by one.

If your STFM has the blue capacitor C49 fitted, this needs to be removed. The capacitors new location will be shown later on.

You need to make sure all the holes as outlined in red are free from solder.

Place the solder pins in the Atari PCB as shown.

TIP - The black plastic part of the pins should be under the 4MB pcb. This will prevent the pins from sticking up though the 4MB pcb too much. The long side of the pins is sticking though the Atari pcb. Raise the motherboard on some sticky tape rolls if needed.

DO NOT SOLDER ANYTHING YET

Place the solder pins in all the holes and place the 4MB pcb on top and solder the pins on the 4MB pcb only. Make sure 100% that all pins have been soldered on the 4MB pcb and make sure 100% you have not missed off any pins!

DO NOT SOLDER THE ATARI SIDE YET

The next part will need the 4MB pcb lifting so that the top of the simm socket is level with , approximately, the top of the metal box.

You need to fit the simm module and make sure it can be fitted and removed with the location of the 4MB pcb. If the 4MB pcb is too low, the chips on the simm catch on top of the metalwork making it impossible to fit the simm in the socket. If the 4MB pcb is mounted too high, it will catch on the bottom of the keyboard & PSU. So it is vital the 4MB pcb can be mounted as low as possible.

TIP - If the simm is known working and not likely to be ever changed, then the simm can be fitted and the 4MB pcb can be mounted as low as it will go. Though be warned that if you need to change the simm after fully fitting the 4MB pcb, then the only "easy" way to remove it, is to unsolder the metal box.

TIP 2 - Use a flashlight to make sure none of the 4MB pins are not touching the underside of the PSU! I recommend gluing a thin square of plastic on the bottom of the psu just to be on the safe side. It is important to make sure the pins ontop of the 4MB PCB are cut as low down as possible!

Once the 4MB pcb has been located , you need to carefully turn the Atari PCB over and solder the pins. Once soldered cut the access pin length off.

TIP - Wear protective goggles when cutting these pins as they can fly across the room, so some eye protection is strongly recommended!

Next up is some metal editing. Draw a rough outline as shown and cut out with a hacksaw.

TIP - A tough junior hacksaw is ideal. The Atari metalwork is pretty tough to cut!

A quick check... Still a bit of metal editing needed but you get the idea!

A file is placed just to show the angle of where the keyboard will go. While the angle of the file touches the top corner of the simm pcb, this isn't actually bad, as the keyboard rests ontop of the Atari's plastic pillars. So the angle of the keyboard is actually a fraction higher than the simm, so it *just* clears it.

TIP - Some simms are taller than others. So its important to find smaller types which I normally supply in the kit.

Its a good idea to part assemble the metalwork and make sure no metalwork is touching the simm board at any point. As you can tell my metal editing skills are not very good, so some more metal editing needed to tidy it up a bit!

A couple other high-res images HERE and HERE.

This image just showing the PSU fits snug back into place.

On the bottom of the Atari pcb solder a small wire as shown to the bottom of the MMU. Note that the TOS rom location is on the left side of the image. Where the wire is soldered there isn't normally any copper tracks going to the pin.

I suggest a VIA hole be unsoldered to allow the wire to go though the Atari pcb to the other side. It isn't too important which hole you use, though I would not recommend routing this wire though a thicker copper track route.

DO NOT SOLDER THE WIRE IN THE HOLE, THE WIRE GOES THROUGH THE HOLE!

The wire is then soldered to the A9 pin on the 4MB PCB. Then SW1 an SW2 are just wire linked to enable 4MB mode. This is assuming you fitted a 4MB simm. Otherwise the link isn't important.

The blue capacitor is refitted as shown. Negative is to the left, positive to the right. The positive hole is on the same track as the small L51 inductor. I actually lost the one I took out so fitted a bigger one ;)

TIP - A small switch can be connected and mounted on the rear of the Atari case if you wish you be able to select from 1MB and 4MB modes. But I would suggest leaving it fixed to 4MB for reliability as a lot of games are patched to run on 4MB machines in more recent years.

I use XTRA_RAM test from marpet development to test the memory. It seems to work well and is a small program and can be downloaded HERE .

A alternative RAM test program developed in 2016. See HERE or you can use the DIAGNOSTIC CARTRIDGE to test the RAM.

Fitting remains the same as previous designs. The 1MB / 4MB switch has been made easier to understand. Also the 2 SMT resistors have been changed for normal resistors.

The 16MB line was removed as the MMU only supports 4MB RAM. While a 16MB simm can be used, A10 is connected to GND to disable the RAM higher than 4MB. I normally supply a ideal 4MB simm with the kit so changing the simm should not be necessary.

There is a 33R and 10K resistor. Unfortunately there was a misprint on some of the PCB's so it looks like "333R" when in actual fact it is "33R". The wire link set 4MB mode. Without the link, it is 1MB mode.

There is a small mod which needs doing to this PCB as shown below.

The link is there to correct a shorted via on the PCB (next to A8) which I have drilled out on all the PCBs. The wire link corrects the problem.

Please check you have no connection (with a meter on resistance test etc) from Where both ends of the wire are shown above to 0V. The wire should be fitted if not you will need to solder a wire as shown above, then make sure there is no short-circuit to 0V.

If you have continuity there, (or just a few ohms) then you need to use a small drill bit and by hand only carefully score away the top copper so it looks like my image above. While you could drill right through the PCB, if you use a drill bit too large, you may damage a PCB track on the rear of the board. In effect we are using a small drill bit is a countersink tool. Only do this by hand (without using a actual drill!)

I supply a length of thin black wire to do this mod (just cut a couple inches off the length supplied). Also the wire is used to connect A9 to the MMU as previously mentioned in the fitting instructions.

These kits are available in my STORE.

The simm adapter is now discontinued and the above SMT based board is now being produced instead.

Fitting remains the same, other than there is no need to hack the shielding now. Fitting should be easier and more straightforward and does not require the removal of the capacitor.

New boards can be purchased here.

https://www.exxosforum.co.uk/atari/store2/#0020