I acquired a 520 STE Tos 1.62 which worked perfectly and I bought an IDE card that is installed on the CPU socket.
I've made two errors on installation
1 / I used a needle to facilitate insertion and I damaged the CPU socket.
2 / I connected the interrupt wire leading from the card to the wrong pin of the ACSI port (Harddrive) : connected in pin 1 instead of pin 10
The result: on the GEM as soon as I'm trying to go to the menu or drive A: 2 bombs are quickly displayed and GEM reboots.
The retailer card kindly proposed to repair my CM with installing a funky socket of Exxos with a tos 2.06. The repair was successful but not completely because I have sometimes two bombs eg. in medium resolution and in some specific Ste games like wings of death (2 bombs each time just at the beginning of the game). With other old games like rick dangerous it works.
Summary of my tests:
-other CPU: same behavior
-test of the 4MB RAM with testram: no mistakes. I swapped the SIMMS and tested with 2MB: not better
- I removed/replaced all the chips socketed chips : not better
- Disk formatting of 82 tracks with fastcopy3: ok
Maybe the chip WD1772 is involved or the Blitter?
If one of you has an idea that would be great!