exxos's Atari, Amiga & retro forum

Hi,
I installed the MMU upgrade to an STFM board Action F C070789-001 Rev.F, TOS 1.04.. The board already had no RAM on it, it was in this state when I received., so thought that made a good candidate for the upgrade. I isolated the R59, 60, 61, 71, 72, 73 resistors and connected to 5V just as it said in the guide although I assume it is unnecessary. The machine boots and seems OK at first. I ran Captain Blood from Utrasatan and Exile from floppy, but when I do the RAM test I get a fail at 2097664. I let it run until it showed 17 times fail. Is it likely damaged RAM or also possible to do with me making bad connections, for example? I have continuity from top of board to bottom of board on the MMU and Shifter. The MMU sits about 2 mm above the socket, I assume this is normal and shouldn't pushed any deeper? I could try the upgrade on an STF board I have, but I am reluctant to mess with the MMU board in case I damage it by removing it.

A picture of it all would help...

exxos wrote: 03 Apr 2021 10:09 A picture of it all would help...

You read my mind.

OK, but I am not a smartphone person who photographs everything he sees so it will take a while. :D

above are photos of what I get, not the best camera ever, need to charge the camera first to make board photos.

To answer one of your other questions, the resistors being tied to 5v isn't necessary if the board has no RAM, as that is what disables any existing RAM. Leaving it as is won't do any harm though.

I'd always suggest that you remove the MMU and clean/tweak the contacts before you do this upgrade to ensure a good contact. It's also important that it is pushed all the way in evenly.

FYI if using YAART you must make sure there are no other things like control panels or drivers, or anything from the auto folder loaded as it can make the test fail. I'd suggest this for any of the RAM testers.

Also can we see some pictures of the mainboard and RAM upgrade please.

There is nothing at the moment in the AUTO folder, but when the Ultrasatan runs there is the driver in memory. I get the same thing with just the floppy drive. As I said at the start the MMU board is not all the way in. I started to get resistance and was a bit unsure. When I test continuity the upper side contacts are connected to the underside of the main board.


I had problems getting my camera to focus close up.

The MMU board looks ok, though you could even it out, it won't go all the way in though, it isn't physically possible, you should be in and be able to see about 2mm of pin all round.

Just as an aside, for this particular I always advise taking the mainboard all the way out and sitting it on a flat surface on a piece of cardboard to avoid flexing as you push down. I've had at least one board go bad pushing something into a socket due to flex.

You may want to check continuity on the MMU board and also check for shorts. I'd also suggest that you try setting the 1MB/4MB to 1MB (If it's on 4MB) and see if the problem goes away.

Does that corruption start right away or does it progressively get worse ?

Hi, the corruption doesn't start right away, but after a program is loaded. I tried with 1 meg, the corruption shows from the start and the ram test fails quickly by 512 and something.
I read the advice about putting the board on a piece of cardboard before I started and followed it. I read a a bunch of posts before I started.. I have evened the MMU board out by puling one side up, the other doesn't go down any further. I checked the continuity of the shifter following the diagram I found from Exxos on another post, I will do the same for MMU. First of all there wont be any more photos because they have all disappeared from the SD card. Have also now damaged my Shifter chip through taking in out too many times. I use the one from the STF board although it is not identical, seems to work fine.