After first building the 30-PIN RAM version, it was fairly easy to work out the wiring for the 72 PIN PC SIMMS, but be warned!!!! with this version, you will find that not many types of 72 PIN RAM work.
When I first built this, I thought my wiring was wrong but after trying many different brands of 72-PIN SIMMS, I eventually found one that works. (And it also runs quite hot !!!)
It also has a lot to do with the type of RAM chips used, the number of RAM chips on the SIMM, the SPEED rate of the RAM chips and also, how many pins are being used out of the 72 PINS.
The C64 will not need all 72 PINS but some types of RAM need these pins to be used and we cant on a C64 , hence many SIMMS I tried did not work.
NOTE: I have a box full of 100+ SIMMS, so I had plenty to try.. AND ONLY ONE WORKED: here are its details:-
SIMM = Stands for SINGLE IN-LINE MEMORY MODULE.
These are mainly found in IBM Compatible Computers in sizes:-
286, 386, 486 = 30 PIN SIMMS
486, Pentium 1 = 72 PIN SIMMS
Pentium 2, Pentium 3 = 168 PIN SIMMS