1040 STFM and Exxos memory upgrade (1/4mb)

[wietze]

Hi there guys,

the past weeks I have been tinkering with the Exxos (2019) memory upgrade on my Rev D stfm board. Being a novice with these things, I decided to remove all chips and put in sockets first, so I could test if my soldering work was actually solid.

The result is, that i have all memory places socketed, and when putting in the memory, sysinfo an yaarrt confirm 1mb of working memory. This makes me to believe soldering the sockets works.

When I remove the memory, and put in the expansion board in the socket; I measured if all pins were actually connected well, using a multimeter. This gave me a beep on every pin, so I believe the memory expansion module is seated well in the sockets.

Following the installation guide, I realized I needed to move capacitor C49, which I did, and move it to the designated place.

I also soldered in the wire from the memory board to pin 64 of the MMU.

However, the resulting configuration does not boot for me, and gives me various situations of bombs (ranging from 4 bombs after disk access, to garbled screen and red colors and trash).

I could do with some suggestions as to how to make progress on this, since Im at a loss.

I can provide photos of the current state if desired.

Kind regards,
Wietze

[rubber_jonnie]

Yes, photos please.

[wietze]

Images attached.

[exxos]

You do need to put that link in for 4MB, but it shouldn't stop 1MB from working. You probably need to try the diagnostic cart with RAM test and YAART to see where the problem is.

[wietze]

I did treat the memory upgrade board roughly during a previous attempt to upgrade another STFM (which I failed at). But the upgrade module doesn't show visible damage apart from some plastic that got removed from the headers.

I currently dont own a diagnostic cartridge. Is there anything else I can try? I will remeasure all connections again tonite to double check.

[exxos]

You could try cleaning the MMU pins in case its got a bad connection.

[wietze]

When the machine has been turned off for a while; and I then start it up; the machine seems to be able to boot significantly further (even to desktop once), than when the machine has been switched on briefly before; then it immediately display bombs.

The machine does not give me this behaviour when the normals rams are inserted and the C49 cap is in its original place. Does this give away any hints or indicators?

[exxos]

I would look at the tweaks and fixes section. Things like PSU and reset circuit etc are common to malfunction.

[wietze]

I would look at the tweaks and fixes section. Things like PSU and reset circuit etc are common to malfunction.

How would you relate this to the memory board malfunctioning, but when the mem upgrade is reverted; the machine works as intended?

[exxos]

How would you relate this to the memory board malfunctioning, but when the mem upgrade is reverted; the machine works as intended?

Different loads on the PSU can cause different issues.