UPDATE:
Today I solved the problem with my Mac IIci. It is fully-functional off of Built-In ROM. Address Line 16 was damaged UNDERNEATH the battery holder. A battery had exploded on this logic board at one point, and leaked through, making A16 intermittent. It passed a continuity check earlier, but not enough for the data to get through.
Unfortunately I discovered this after removing the ROMs, after which I removed the battery holder. I soldered the ROMs back on, and it works!
I plan to remove the ROMs again and install DIP-32 to PLCC-32 socket adapters. Then I can freely burn inexpensive flash chips with modded ROM! Endless fun is planned.
It has crossed my mind to expand the 512kiB limit to 1024kiB. I believe that this is as simple as connecting A17 on the new ROMs to pin 42 in the ROM SIMM slot. Does anyone see a reason this wouldn't work? With a 1024kiB limit, I could attempt to burn with a Mac LC II ROM code. IMAGINE a Mac IIci, not only with the newer startup sound, but customizable startup sound! OMG. But we'll have to see if the LCII ROM works first and/or how far off it is.
Anyone have a clue whether the A17 to pin 42 thing is likely to work? It seems logical to me.
Today I solved the problem with my Mac IIci. It is fully-functional off of Built-In ROM. Address Line 16 was damaged UNDERNEATH the battery holder. A battery had exploded on this logic board at one point, and leaked through, making A16 intermittent. It passed a continuity check earlier, but not enough for the data to get through.
Unfortunately I discovered this after removing the ROMs, after which I removed the battery holder. I soldered the ROMs back on, and it works!
I plan to remove the ROMs again and install DIP-32 to PLCC-32 socket adapters. Then I can freely burn inexpensive flash chips with modded ROM! Endless fun is planned.
It has crossed my mind to expand the 512kiB limit to 1024kiB. I believe that this is as simple as connecting A17 on the new ROMs to pin 42 in the ROM SIMM slot. Does anyone see a reason this wouldn't work? With a 1024kiB limit, I could attempt to burn with a Mac LC II ROM code. IMAGINE a Mac IIci, not only with the newer startup sound, but customizable startup sound! OMG. But we'll have to see if the LCII ROM works first and/or how far off it is.
Anyone have a clue whether the A17 to pin 42 thing is likely to work? It seems logical to me.