Hi Motor,
Did the A3000D boot up properly before you started adding RAM? Or did it go to a yellow screen for no apparent reason one day?
I assume the 8 20-pin DIP sockets (U850D-U857D) are empty and that the 8 ZIP sockets at U850-U857 have the 1Mx4 ZIPs? Both these groups are considered Bank 0 and you won't be able to power up properly if they're both populated. Also, it is important that one does not mix ZIP RAM densities.
You also have to populate the following banks in sequence, starting from Bank 0 or it won't work:
Bank 0 (8 ZIPs) U850-U857
Bank 1 (8 ZIPs) U858-U865
Bank 2 (8 ZIPs) U866-U873
Bank 3 (8 ZIPs) U874-U881
This might be of further use to you (A3000D User Manual, quite detailed for a "User" manual):
http://oldcomputers.net/Amiga_3000_manual.pdf
