I have a 3561A, and have never encountered need for any kind of special module, but I did have to do something in the menu/setup/diagnostic controls. There is a re-something function built into the machine, to basically restart/re-format the bubble memory from scratch. As I recall, it was because the backup battery (for the processor - not for the bubble memory function per se) was dead, so you had to totally reboot everything. I think the battery-backed data has info on running the bubble memory, so if it's lost, you have to start over. The manual definitely has the answer, but not necessarily in an obvious way. If I think of anything else on this, I'll report on it. Good luck.
Ed
