In the following picture you can see a close-up of the 65C102 co-processor board. The major components are the 65C102 processor, the RAM and ROM and the Tube IC (that controls communication with the host computer):
The 65C102 co-processor has a 65SC102 CPU clocked at 4MHz and 64Kbytes of memory.
The following image shows the schematic diagram for the co-processor board (note: this schematic is for the original BBC Micro 6502 second processor. The 65C102 is functionality equivalent but has a different number of ICs):
The following picture shows the top-side of the co-processor’s PCB (with the components removed):
The following picture shows the bottom-side of the co-processor’s PCB: