exxos's Atari, Amiga & retro forum

rubber_jonnie wrote: 22 Apr 2021 16:11 A faulty glue in the 520ST I got from you gave me FDD problems.

GLUE pretty much has its hands in everything. One bad address line to it and you can have multiple faults all over the machine.. Of course bad address lines can be also a symptom of mandatory fixes not been done.

Yes, I did that before I ever posted, I read lots of info from the board before getting that far. I don't really like asking for help. After all, its been going for years and there are lots of posts on the same subjects. The only problem I had was when I do a search and get say 200 results, I can normay only view the first page and then it doesn't let me go further, so the possibility of missing relevant posts from the past is high. I know the board is run by a third party. So I need to sign off for today, thanks for all contributions. :)

Short update after nearly a year. I used the same upgrade on a different board and it seems to work fine. I also have the same shifter chip which I broke the pin off. I bunged lots solder on it and it also seems to work. I also soldered another shifter board from scratch. I had no reason to believe the other one was faulty, just fancied the challenge as I have more idea of what I am doing now and am better equipped. My eyes and hands are still a bit old and knackered, though. :D In other words if your board is in order these upgrade kits run without problems. The original STFM board I will at some point mess around with and try to see what I can find.

russellnash wrote: 31 Mar 2022 14:33 Short update after nearly a year. I used the same upgrade on a different board and it seems to work fine. I also have the same shifter chip which I broke the pin off. I bunged lots solder on it and it also seems to work. I also soldered another shifter board from scratch. I had no reason to believe the other one was faulty, just fancied the challenge as I have more idea of what I am doing now and am better equipped. My eyes and hands are still a bit old and knackered, though. :D In other words if your board is in order these upgrade kits run without problems. The original STFM board I will at some point mess around with and try to see what I can found

These types of upgrade do rely on a lot of things being 'just right', especially with the PLCC sockets, so good to hear you've been able to put it to use.

It pays to keep bashing away at things. After over two years I have got the original STFM board working. I fitted this type of 4mb upgrade. I ended up sometimes with a white screen, sometimes with black and white stripes. The halt pin 17 of the CPU was mostly stuck low. The inverters of the U1 74LS chip on the reset circuit weren't working very reliably, so I changed that chip. It still didn't boot.
Pin 20 on the TOS Roms was always stuck high. The U68 74LS11 NAND gate for the two chip TOS was receiving a high input at pins 9,10 and 11. The output at pin 8 was stuck high.
I replaced the U68 chip and it booted. The RAM passed the memory test without problems, no screen corruption.

:bravo:

Note the LS11 is a AND gate. If any of the 3 inputs are low, the output will be low.