4MB RAM Upgrade for Atari STFM 520 C103253 Rev 1 Board

[friijy2001]

Hi everyone, Purchased a few upgrades for this machine from the Exxos store so thought I would post here just in case others have the same board as its a little different to some I have seen.


As you can see, different RAM chips than I am used to, a blank space for a blitter (Am thinking this is a late STFM board before the STE) and where the MMU will go seems to be pointing in a different direction. Also 2 TOS chips, currently 1.02 but have purchased the 1.04 too.

RAM isolation..... I have cut the pins on the gold side of the resistors (R59 - R61) joined them together and ran a wire to the + of the large capacitor as you can see below...


I have popped a bit of hot glue in place, mainly to stop anything connecting when it shouldn't, I will remove the rest of the RAM and Capacitors on the left hand side of the top photo once a test has been done.

Onto the MMU....I mentioned it was round the other way compared to the instructions so will have to mount it shown below...


I will also remove the sockets for the shifter before installing, also note I have already joined cables to select a switch from 1MB to 4 MB. I have been testing the connections as they go and the machine was fully working before taking apart so fingers crossed the rest of the install should go to plan

So at this stage I suppose its a very quick question to the forum, am I doing everything right?

[exxos]

It looks OK at a glance... Main thing is to make sure you match pin 1 on the MMU board to the MB.. There is info on my site about that anyway.

[rubber_jonnie]

IIRC this mainboard has the MMU reversed compared to say a CO70789, for what reason I don't know.

Looking at a photo of one of my upgrades with this kit, the Pin 1 end is the opposite end to the socket for the ribbon cable, which means yours is fitted correctly.

I'd check that you have the adapter pushed down far enough into the MMU socket, and I'd even go so far as to say remove it from the machine and any shielding, so that when you push down it goes in evenly and the board doesn't flex.

Check for bent pins too, although it is difficult to do, it isn't impossible and will stop things working.

It's unlikely that with the Shifter shield fitted you would fit the adapter there wrong, but double check nonetheless, and finally make sure the ribbon cable is fitted with the blue writing facing up and not down.

Bad connections are the most likely problem, so you may also want to do this: viewtopic.php?f=17&t=1484&hilit=plcc to the MMU socket ans clean all the contacts and reassemble before trying again.

Incorrect assembly does happen too, somebody posted a problem on here recently for the same kit in a Mega, but their Shifter adapter was plugged in 180 degrees out. Worked fine when they refitted it in the correct orientation.

[friijy2001]

Thank you for that I haven’t seated the MMU yet as I wanted to check first so that’s good!

I have put this on hold for tonight, mainly as my solder sucker has just died so I have a new one being delivered tomorrow, once this arrives I’ll start taking off the risers so the upgrade fits nicely to the board.

I am doing the TOS switcher as the same time as I have the ST open

[friijy2001]

All installed, I checked the circuit tracks once I soldered in the parts onto the motherboard to make sure they connected to where needed and I had not damaged the main board whilst removing the old risers.

Did a syscheck and it all works!

A few more bits before I close the lid on this and thank you for your help

[exxos]