UPDATE
I have acquired some PLCC-32 to DIP-32 adapters and installed them in place of the onboard ROMs of this Mac IIci.
Unfortunately there was a SHORT in one of the adapters that I didn't notice until after installation. I discovered this with a continuity tester after the Mac failed to chime from the ROM SIMM slot. A6 was shorted to A15. My solution was ingenious. I did not have to remove the adapters, which would have been almost impossible.
I have a current-controlled voltage source. I set it to 1 volt, turned the current down a ways and applied the voltage across A6 to A15 of each adapter. I also attached a voltmeter across these two at the same time. Since the traces have resistance, I knew the one with the LOWEST voltage reading would be the one with the short circuit.
Once I knew that, I had a look at the 5th adapter I ordered and determined the exact spot the short had to be. I crafted a tool out of a piece of 14-gauge steel wire and filed a rasp into the end. With this tool, I was able to reach under the adapter and scrape back and forth to remove the solder that was bridging the two address lines.
MORALS OF THE STORY:
Test parts before installing
REALLY test parts that you ordered on eBay from China
So now it works again off of the IIfx ROM SIMM after I removed that short. I tested continuity of each address and data pin from the SIMM slot to the onboard ROM and Found one open circuit. I must have cracked or lifted a trace, so I found another point nearby and added a short 1" jumper. In theory this should be fully-functional now.
I also connected two additional address bits from the ROM SIMM slot to the appropriate pins on the adapters. This is on the bottom of the board (not seen in picture). The AT29C020 chips I have will use one additional address bit, for a total of 1 MByte ROM, with easy expansion to 2 MByte ROM by substituting 040 ROM chips.
All I have to do next is get access to a ROM burner!! First I want to try the normal IIci ROM just to verify that it's working and that I split the ROM up correctly amongst the 4 chips, etc. Then I'll be moving on to Mac LC II ROM. We'll see what happens! I've never heard of anyone trying a 1 MByte ROM in a Mac IIci.
I have acquired some PLCC-32 to DIP-32 adapters and installed them in place of the onboard ROMs of this Mac IIci.
Unfortunately there was a SHORT in one of the adapters that I didn't notice until after installation. I discovered this with a continuity tester after the Mac failed to chime from the ROM SIMM slot. A6 was shorted to A15. My solution was ingenious. I did not have to remove the adapters, which would have been almost impossible.
I have a current-controlled voltage source. I set it to 1 volt, turned the current down a ways and applied the voltage across A6 to A15 of each adapter. I also attached a voltmeter across these two at the same time. Since the traces have resistance, I knew the one with the LOWEST voltage reading would be the one with the short circuit.
Once I knew that, I had a look at the 5th adapter I ordered and determined the exact spot the short had to be. I crafted a tool out of a piece of 14-gauge steel wire and filed a rasp into the end. With this tool, I was able to reach under the adapter and scrape back and forth to remove the solder that was bridging the two address lines.
MORALS OF THE STORY:
Test parts before installing
REALLY test parts that you ordered on eBay from China
So now it works again off of the IIfx ROM SIMM after I removed that short. I tested continuity of each address and data pin from the SIMM slot to the onboard ROM and Found one open circuit. I must have cracked or lifted a trace, so I found another point nearby and added a short 1" jumper. In theory this should be fully-functional now.
I also connected two additional address bits from the ROM SIMM slot to the appropriate pins on the adapters. This is on the bottom of the board (not seen in picture). The AT29C020 chips I have will use one additional address bit, for a total of 1 MByte ROM, with easy expansion to 2 MByte ROM by substituting 040 ROM chips.
All I have to do next is get access to a ROM burner!! First I want to try the normal IIci ROM just to verify that it's working and that I split the ROM up correctly amongst the 4 chips, etc. Then I'll be moving on to Mac LC II ROM. We'll see what happens! I've never heard of anyone trying a 1 MByte ROM in a Mac IIci.