Arduino with 12 bit DAC (MCP4725) Not Working
you want to make sure that there are pull-ups on the SCL/SDA lines;
you want to make sure that the address is correct. some routines use 7-bit notation for that, and others use 8-bit notation for that. end of the day, you want the transmission to be 0xc0 | (A2:A1:A0:R/W). so check the write.write() and see what it expects. I suspect that it expects 0xCx, rather than 0x6x.


having said that, here is your code running on an uno, with the dac configured as per sparkfun spec.



so I think it is fair to say that the code is ok but something happened on your end that prevented it from working.