Model System Board Description 1540 1540001-01 Long board. 1541 1540001-03 Only the ROMs are different. 1540048-01 Short board with a 40 pin gate array (Alps). 1540048-03 Short board with a 40 pin gate array (Newtronics). SX64 250410-01 Most similar to 1540048-01. 1541A 250442-01 Alps or Newtronics drive selected by a jumper. 1541A2 250446-01 A 74LS123 replaces the 9602 at UD4. 1541B 250448-01 Same as the 1541C, but in a case like the 1541. 1541C 250448-01 A new 40/42 pin gate array, a 20 pin gate array and a R/W hybrid chip replace many components. Uses a Newtronics drive with track 0 sensor. 1541-II A complete redesign using the 40 pin gate array from the 1451C and a Sony R/W hybrid, but not the 20 pin gate array. NOTE: These system boards are the 60 Hz versions. The -02 and -04 boards are probably the 50 Hz versions. The ROMs appear to be completely interchangeable. For instance, the first version of ROM for the 1541-II contained the same code as the last version of the 1541. I copy the last version of the 1541-II ROM into two 68764 EPROMs and use them in my original 1541 (long board). Not only do they work, but they work better than the originals.