I just installed a vers. 3.1 A3640 into my A3000D that worked fine in my A4000D. I set the recommended jumpers per the above link and went to boot. I got the guru meditation screen because the SCSI drives installed softkicked 3.1 ROMS. So I removed the HDD and booted into WB2.1 via DF0 since this A3000D has 2.04 ROMS. All checked well with the 68040 processor recognition in SysInfo, but I noticed the FPU and the MMU were disabled. The speed check was marginally slower then the stated speed for a 040 A4000, but I was sure the disabled FPU and MMU caused that. Does anyone know how Enable those features on the A3640? I have checked and the chip is in fact a 68040RC25.
