pinto_guy
Well-known member
I'm not having too much luck posting my issue on an old thread in this forum, so I'll start a new one.
I'm trying to convert my Mac XL back to a 2/10 model. To start with, I took the CPU board from the XL, swapped the two ROMs and the VSROM chip from my good 2/10, inserted this converted XL CPU board in my 2/10, and confirmed that it worked OK.
So you'd say I just need to copy the two H ROM's using an EPROM programmer, and burn into two blanks EPROM's and that should work, right ?
Well, it did not work. The copies I made (341-075-A and 76-A) are bit-by-bit the same as the ones that can be downloaded from bitsavers.org (using the DOS FC command), but I cannot boot or even see a good video screen out of the new EPROMs. If I replace with the original H-ROM chips, everything works, even though they're supposed to be bit-by-bit the same. I am clearly missing something here. Could it be something in the hardware itself ? Read voltage perhaps. I need to point out that my original EPROM's are Hitachi HN482764, and the new ones are AM2764DC (AMD) chips. They're both type 27, 64k, 28pins chips, and should be somewhat equivalent.... or not ?
Would anyone have any idea what's happening ?
I'm trying to convert my Mac XL back to a 2/10 model. To start with, I took the CPU board from the XL, swapped the two ROMs and the VSROM chip from my good 2/10, inserted this converted XL CPU board in my 2/10, and confirmed that it worked OK.
So you'd say I just need to copy the two H ROM's using an EPROM programmer, and burn into two blanks EPROM's and that should work, right ?
Well, it did not work. The copies I made (341-075-A and 76-A) are bit-by-bit the same as the ones that can be downloaded from bitsavers.org (using the DOS FC command), but I cannot boot or even see a good video screen out of the new EPROMs. If I replace with the original H-ROM chips, everything works, even though they're supposed to be bit-by-bit the same. I am clearly missing something here. Could it be something in the hardware itself ? Read voltage perhaps. I need to point out that my original EPROM's are Hitachi HN482764, and the new ones are AM2764DC (AMD) chips. They're both type 27, 64k, 28pins chips, and should be somewhat equivalent.... or not ?
Would anyone have any idea what's happening ?