3000 HD (250-4010/4011) Math Coprocessor Faxback Doc. # 1389 Note: Refer to Faxback Doc. # 1173 for Main Logic Board Layout. Contact the nearest Radio Shack Store for the catalog number of the correct Math Co-processor for your computer. There is a co-processor socket on the main logic board at location U78 on the NON-GATE ARRAY version or at location U32 on the GATE ARRAY version. All you have to do is plug the co-processor chip into the 3000 HD main logic board.